Pre-sintered multi-layer dental mill blank, method of preparation and use thereof, and method of sintering

Abstract

The present invention relates to a pre-sintered multilayer dental mill blank comprising a top layer, a bottom layer and at least one intermediate layer. When fully sintered by a rapid sintering process, the pre-sintered multilayer dental mill blank, or portions made therefrom, has one or more desirable properties. The invention also relates to a method for producing a dental restoration using a pre-sintered multilayer dental mill blank, and to the dental restoration itself. The invention also relates to a method for sintering a dental restoration precursor.

Description

[0001] Priority application

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 485,147, filed on February 15, 2023, and European Patent Application No. EP 23156705, filed on February 15, 2023. The entire contents of the priority applications are hereby incorporated by reference herein for all purposes. Technical Field

[0003] The present invention relates to a pre-sintered multilayer dental mill blank and a method for producing the pre-sintered multilayer dental mill blank. The present invention also relates to a dental restoration obtainable from the pre-sintered multilayer mill blank. The present invention also relates to a method for sintering a dental restoration precursor. Background Art

[0004] It is generally desirable for dental restorations to resemble the appearance of natural teeth and / or match the appearance of adjacent teeth in the patient's mouth. While the appearance of natural teeth can vary, there are certain optical characteristics that can be considered universal for most natural human teeth. Natural teeth typically have a color and / or translucency that varies from the upper incisal or occlusal portion of the tooth to the lower dentin portion. The upper incisal or occlusal portion typically has a higher translucency and may be lighter than the lower dentin portion. The portion of the tooth between these two portions typically exhibits some gradual change or transition in color and translucency. In addition to the obvious aesthetics of a dental restoration, a dental restoration should have adequate mechanical properties and be long-lasting and durable. The preparation of a personal dental restoration should be quick and efficient so that the patient receives adequate treatment within a short time from start to finish at the dentistry or dental care center.

[0005] In modern dentistry, dental restorations are typically made from ceramic materials such as zirconium oxide ceramic materials. Ceramic dental restorations are typically made from dental ceramic mill blanks. Dental ceramic mill blanks are typically porous and not fully sintered in order to provide the mill blank with suitable machinability and processability, such as in CAD / CAM methods. Multilayer dental mill blanks are available in the art, which contain different ceramic materials in different layers from the top to the bottom of the mill blank. The purpose of these dental mill blanks is to provide a dental restoration with a gradual change in optical appearance from the incision area of ​​the restoration to its dentin area. In order to prepare the final dental restoration, a ceramic dental restoration precursor is first machined from the dental mill blank. This dental restoration precursor typically has the shape of the final ceramic dental restoration, but has not yet reached its final density and, therefore, its final size. In order to provide a ceramic dental restoration of final density and size, the dental restoration precursor needs to undergo a final sintering process. The final properties (such as optical properties) of the ceramic dental restoration are strongly affected by the final sintering process. To achieve satisfactory results for dental restorations, a relatively long final sintering process, such as a sintering process with a total duration of several hours, is usually required. Consequently, the final sintering process accounts for a large portion of the time required to produce personalized ceramic dental restorations and significantly increases the time required to provide the desired treatment to the patient.

[0006] It is desirable to shorten the final sintering process in order to reduce the overall time required to produce a dental restoration. This is particularly relevant when aiming to allow short processing times for so-called chair-side (as opposed to laboratory-side) applications, in which the final dental restoration can be provided to the patient during a single visit. However, attempts to significantly shorten the final sintering time using known multi-layer dental mill blanks have resulted in dental restorations with unsatisfactory properties, such as unsatisfactory optical properties. For example, the dental restoration may have an unnatural appearance, for example, it may not exhibit a uniform variation in optical properties across different areas of the restoration.

[0007] There is an ongoing need in the art for a dental mill blank suitable for providing a dental restoration precursor that can be sintered to full density in the shortest possible time while providing a dental restoration with good optical appearance. Summary of the Invention

[0008] It is an object of the present invention to at least partially overcome one or more disadvantages of prior art dental mill blanks. It is an object of the present invention to provide a dental mill blank that allows for improved patient convenience, such as chair-side application, and at the same time provides an attractive aesthetic of the dental restoration. It is an object of the present invention to provide a dental mill blank that is suitable for providing a dental restoration with desired properties, such as optical properties. It is an object of the present invention to provide a dental mill blank that is suitable for preparing a dental restoration precursor that can be sintered to full density in a relatively short time, while providing a dental restoration with desired properties, such as desired optical properties, like a gradual increase in translucency from the dentin area to the incisional area.

[0009] Embodiments and aspects of the present invention at least partially address at least one of the above-mentioned objects.

[0010] One aspect of the present invention provides a pre-sintered multi-layer dental mill blank comprising a top layer, a bottom layer, and at least one middle layer.

[0011] In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer having increasing contrast from the top layer to the bottom layer when fully sintered by a rapid sintering process.

[0012] In one embodiment, the pre-sintered multilayer dental mill blank is characterized by providing a representative test cross section of each layer having a CIE lightness L* that increases from the bottom layer to the top layer when fully sintered by a rapid sintering process.

[0013] In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer, and when fully sintered by a rapid sintering method, a representative test cross-section of the top layer and / or an intermediate layer adjacent to the top layer has a pore count per grain of less than 0.25.

[0014] In one embodiment, each layer of the pre-sintered multilayer dental mill blank comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, and the top layer comprises a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof).

[0015] In one embodiment, each layer of the pre-sintered multi-layer dental mill blank comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, and the top layer comprises aluminum oxide in an amount less than 0.01 wt. % based on the total weight of the top layer.

[0016] One aspect of the present invention provides a method for preparing a pre-sintered multi-layer dental mill blank, the method comprising the steps of:

[0017] a) providing three yttria-stabilized zirconium oxide powders P1 to P3, powder P1 having an yttria content in the range of 4.5% to 6.1% by weight, powder P2 having an yttria content in the range of 6.2% to 7.9% by weight, and powder P3 having an yttria content in the range of 8.0% to 11.0% by weight,

[0018] b) preparing a green body consisting of:

[0019] The top powder layer of powder P3,

[0020] at least one intermediate powder layer of a powder mixture chosen from a mixture of powders P2 / P3 and a mixture of powders P1 / P2,

[0021] a bottom powder layer of powder P1 or a mixture of powders P1 / P2,

[0022] c) pre-sintering the green body to provide a pre-sintered multi-layer dental mill blank.

[0023] Another aspect of the present invention provides a method for preparing a dental restoration, the method comprising the steps of: machining a pre-sintered multi-layer dental mill blank according to any one of the embodiments of the present invention to provide a dental restoration precursor; optionally surface treating the dental restoration precursor and sintering the dental restoration to provide a dental restoration.

[0024] Another aspect of the present invention provides a dental restoration obtainable by the method for producing a dental restoration according to any one of the embodiments of the present invention.

[0025] Yet another aspect of the present invention provides a method for sintering a dental restoration precursor, said method having a total duration of less than 25 minutes and a maximum sintering temperature in the range of 1350° C. to 1650° C.

[0026] The method comprises subjecting the dental restoration precursor to

[0027] (i) heat treatment, and

[0028] (ii) cooling treatment,

[0029] The cooling process comprises a cooling step A which starts and ends in a temperature range between 1100° C. and the maximum sintering temperature and has a cooling rate A of at least 75 K / min.

[0030] definition

[0031] In the context of the present invention, the following terms have the following meanings:

[0032] As used herein, "sintering" means densifying a porous ceramic material into a lower porosity material having a higher density by subjecting the porous ceramic material to heat at a suitable temperature, which is below the melting point of the major components of the ceramic material, to densify the material.

[0033] As used herein, "pre-sintered" or "pre-sintering" means subjecting a ceramic green body to heating in order to partially or completely remove or decompose an organic binder, an inorganic binder, or a thermally unstable component. Pre-sintering typically results in at least partial formation of sinter necks at the boundaries of connected particles in the ceramic material and results in thermal hardening of the ceramic material, which contributes to the workability or machinability of the material. The relative densification from the ceramic green body to the pre-sintered ceramic material is typically 5% or less relative to the size of the ceramic green body. The pre-sintered ceramic material typically has an open porous structure that can be further densified when the material is fully sintered in a subsequent sintering step. The density of the pre-sintered ceramic material (such as a pre-sintered zirconia ceramic) can be in the range of 45% to 70% relative to the theoretical density of the ceramic material. For zirconia ceramic materials, pre-sintering is typically carried out at a maximum temperature of 700°C to 1200°C. The temperature at which the ceramic body is pre-sintered can be determined by one skilled in the art, for example, by measuring thermal expansion using a dilatometer.

[0034] As used herein, "fully sintered" or "fully sintered" means that the ceramic material has been sintered to at least 98.5%, such as at least 99.5% or at least 99.8% of the theoretical density of the ceramic material. The density of the material can be determined by Archimedes' method according to DIN EN 623-2, or can also be determined by weighing the material and geometrically determining its volume. Those skilled in the art can, for example, determine the theoretical density of a fully sintered material based on the composition of the material. Additionally or alternatively, the theoretical density of the ceramic material can be determined by grinding the ceramic material into a powder having a volume median particle size in the range of 10 μm to 30 μm (e.g., 20 μm), and determining the density of the powder by a pycnometer. The volume-based median particle size can be determined by laser diffraction, for example, according to ISO 13320 (2009). The layers of a multilayer dental mill blank may have different theoretical densities, depending on the ceramic material present in each layer. In this case, the density of the ceramic material and the theoretical density can also be determined separately for each layer.

[0035] A "green body" is a molded body of ceramic powder that has not been subjected to a sintering or pre-sintering step and typically contains an organic binder, an inorganic binder or other additives. The molded body is typically prepared by compacting (eg, pressing) the ceramic powder.

[0036] As used herein, "porous" means that the material has pores, and is meant to include open porous materials and closed porous materials. "Open porous" materials are materials with pores that are at least partially interconnected and at least partially accessible from the outside, for example, by the flow of a gas or liquid. Open porous materials as defined herein may also have pores that are inaccessible from the outside, for example, by the flow of a gas or liquid. "Closed porous" materials are materials that are non-open porous and have closed pores (i.e., pores that are inaccessible from the outside, for example, by the flow of a gas or liquid). "Porosity" is a measure of the void space (e.g., pores) in a solid material, and is the fraction of the volume of the void space to the total volume of the solid material. It can be expressed as a percentage from 0 to 100%.

[0037] "Multi-layer" means having at least three layers, ie a "multi-layer dental mill blank" is a dental mill blank having at least three layers.

[0038] "Dental mill blank" means a solid, geometrically defined three-dimensional object of material, such as a block or disk, that can be machined into a dental article, for example, by cutting, grinding, milling, drilling, or the like.

[0039] As used herein, "dental restoration" refers to an article that can be used in the dental or orthodontic fields to repair, reshape, support and / or reconstruct a tooth or part thereof or a group of teeth or parts thereof. A dental restoration can be, but is not limited to, a crown, a partial crown, an abutment, an abutment crown, an inlay, an onlay, a veneer, a shell, or a bridge.

[0040] As used herein, "dental restoration precursor" refers to a workpiece machined from a dental mill blank which already has the shape of a dental restoration but has not yet been fully sintered and, therefore, has not yet reached its final dimensions.

[0041] "Layer" means a discrete layer of a pre-sintered multi-layer dental mill blank having one or more (usually more than one) substantially uniform properties within the dimensions of the layer. The one or more properties may be optical properties when fully sintered (e.g., CIE L*a*b* values ​​or contrast ratio determined as described herein) and / or the amount of one or more base components (e.g., zirconium oxide and / or yttrium oxide). In this context, "substantially uniform" should be understood as having substantially the same value or property within the layer regardless of the measurement location, allowing for tolerances due to unavoidable manufacturing variability and / or measurement deviations as described herein.

[0042] As used herein, "contrast ratio" refers to the ratio of the illuminance (Y) of a material placed on a black background (Yb) to the illuminance of the same material placed on a white background (Yw) (CR = Yb / Yw). Contrast ratio can be determined according to BS 5612, in particular BS 5612:1978. A suitable device for measuring contrast ratio is, for example, a spectrophotometer CM 3700-D (Konica-Minolta). Contrast ratio can be used to characterize the translucency of a material, i.e., the light transmittance of a material, expressed as the ratio of the intensity of the transmitted light to the intensity of the incident light. A contrast ratio close to 0% may indicate that a given material is almost completely transparent, while a contrast ratio of 100% may indicate that the material is completely opaque.

[0043] The CIE (Commission Internationale de l'Eclairage, International Commission on Illumination) l*a*b* (CIELAB) values ​​are used to characterize the color of a material using a three-dimensional color space. The individual color L* is a measure of the luminance brightness, and it is represented on the vertical axis of the color space. The a* and b* coordinates are measures of the chromaticity and are represented on the horizontal coordinates of the color space, with positive a* representing red, negative a* representing green, positive b* representing yellow, and negative b* representing blue. The CIE L*a*b* values ​​can be measured according to DIN 6174. A suitable device for measuring contrast is, for example, a spectrophotometer CM 3700-D (Konica-Minolta).

[0044] As used herein, "top layer" refers to the outermost layer of a multi-layer dental mill blank that can be used to prepare at least a portion of an incision or occlusal area in a dental restoration that can be obtained from the mill blank by machining and sintering.

[0045] "Intermediate layer" means a layer located between the top and bottom layers of a pre-sintered multilayer dental mill blank. At least one intermediate layer can be used to prepare at least a portion of a transition zone of a dental restoration obtainable from the mill blank by machining and sintering.

[0046] "Base layer" means the outermost layer of a multilayer dental mill blank located on the opposite side of the multilayer dental mill blank relative to the top layer. The base layer can be used to prepare at least a portion of the dentin zone of a dental restoration obtainable from the mill blank by machining and sintering.

[0047] The terms "top layer," "middle layer," and "bottom layer" should not be interpreted as meaning that the multilayer dental mill blank needs to be positioned in a specific manner or orientation. Furthermore, any other portion or layer (e.g., a supporting layer, a protective layer, a printed layer, or a sacrificial layer) that is otherwise present on the outside of the multilayer dental mill blank and is not intended to be part of the dental article to be machined from the multilayer dental mill blank should not be understood as the top layer, middle layer, or bottom layer of the pre-sintered multilayer dental mill blank, or should not be considered part of the dental mill blank. In one embodiment, the pre-sintered multilayer dental mill blank is attached to another portion or layer, such as, but not limited to, a fixing pin, a supporting layer, a protective layer, a printed layer, or a sacrificial layer, on one or more of its outer sides (e.g., a layer on its outer sides). The sacrificial layer can be, for example, a thin ceramic layer that will be removed when the dental article is machined from the pre-sintered multilayer dental mill blank.

[0048] As used herein, "fast sintering process" refers to a sintering process for producing a fully sintered ceramic material from a ceramic material precursor, the total duration of which is less than 45 minutes.

[0049] As defined herein, a "sintering method" means a series of controlled temperature adjustment steps (e.g., controlled heating, holding or cooling steps) performed in a sintering furnace. "Controlled" means that the heating or cooling rate is actively adjusted to a predefined value by a control device such as a furnace, as opposed to, for example, uncontrolled "cooling", in which no active adjustment of the cooling rate occurs. The sequence is typically programmed into the sintering furnace before the sintering method begins. "Cooling" as defined herein is not part of the sintering method as defined herein. "Cooling" refers to a cooling phase that begins after the final controlled temperature adjustment step (e.g., a final controlled cooling step) is completed. Cooling can occur at least partially in an open sintering furnace. Cooling typically takes several minutes (e.g., 2 to 8 minutes). Cooling is generally considered to be completed at a temperature in the range of 300°C to 400°C. Of course, it is also possible to cool to a lower temperature, such as room temperature. As defined herein, the "total duration" of a sintering process refers to the time elapsed through all controlled temperature conditioning steps of the sintering process (i.e., including all controlled heating steps, holding steps, and cooling steps, but excluding cooling). As used herein, "room temperature" refers to a temperature in the range of 15°C to 50°C.

[0050] Unless expressly stated otherwise, the "yttria content" or "amount of yttria" (the two expressions are used interchangeably herein) of an article (e.g., a powder, composition, layer, or mill blank) refers to the total amount of yttria present in the article, regardless of how the yttria is introduced into the article. When yttria content is defined herein, it may include both type I yttria and type II yttria. "Type I yttria" or "type I yttria content" as defined herein refers to yttria or the yttria content present in an yttria-stabilized zirconia powder used to prepare at least a portion of a powder layer of a green body from which a pre-sintered multilayer dental mill blank can be obtained by pre-sintering. Therefore, when the yttria content of a yttria-stabilized zirconia powder is described herein, this yttria content is generally the type I yttria content. As defined herein, "type II yttrium oxide" or "type II yttrium oxide content" refers to yttrium oxide that can be obtained by converting a yttrium salt into yttrium oxide during pre-sintering of a green body of a multi-layer dental mill blank. For example, the surface of a powder particle can be treated with a yttrium salt. Subsequently, the surface-treated powder particles can be used to prepare a powder layer of a green body, wherein the yttrium salt can be at least partially located at the boundaries between different particles. When the green body is pre-sintered, the yttrium salt is converted to type II yttrium oxide. Type II yttrium oxide may segregate at grain boundaries during and / or after pre-sintering.

[0051] "Yttria-stabilized zirconia" means zirconia that is at least partially present in a tetragonal or cubic phase and that has an amount of yttria incorporated into its crystal lattice that is sufficient to at least partially prevent the transformation of the tetragonal and cubic phases, respectively, into a monoclinic phase during cooling to room temperature. At room temperature, pure zirconia exists in the most stable crystalline phase (monoclinic phase). When the temperature of the zirconia is raised to about 1170°C, the monoclinic phase transforms into the tetragonal phase, and then at about 2370°C the tetragonal phase transforms into the cubic phase. Incorporating an appropriate amount of yttria into the crystal lattice of the zirconia at least partially stabilizes the tetragonal or cubic phase of the zirconia, i.e., at least partially prevents the transformation of the tetragonal and cubic phases, respectively, into the more stable (at room temperature) monoclinic phase of zirconia. Depending on the amount of yttria incorporated into the crystal lattice of the zirconia, the yttria-stabilized zirconia can be provided in the form of its tetragonal phase, in the form of a mixture of its tetragonal and cubic phases, or in the form of its cubic phase. For example, a yttria-stabilized zirconia containing about 3 mol% yttria can be provided in its tetragonal phase without a substantial amount of cubic phase. A yttria-stabilized zirconia containing about 4 mol% or 5 mol% yttria can be provided as a mixture of tetragonal and cubic phases. A yttria-stabilized zirconia containing about 8 mol% or more yttria can be provided in its cubic phase.

[0052] As used herein, a "sintering activator" is a metal oxide that is added to a ceramic material (e.g., yttria-stabilized zirconia) and shifts the temperature required to achieve a specific densification in the (final) sintering process of the ceramic material to a lower temperature range. The sintering activator can be added to the ceramic material in the form of a sintering activator precursor. As used herein, a "sintering activator precursor" refers to a metal salt that can be converted to a metal oxide during a heating step (e.g., during a pre-sintering step) to provide a metal oxide that serves as a sintering activator.

[0053] As used herein, a "sintering inhibitor" is a metal oxide that is added to a ceramic material (e.g., yttria-stabilized zirconia) and shifts the temperature required to achieve a specific densification in the (final) sintering process of the ceramic material to a higher temperature range. The sintering inhibitor can be added to the ceramic material in the form of a sintering inhibitor precursor. As used herein, a "sintering inhibitor precursor" refers to a metal salt that can be converted to a metal oxide during a heating step (e.g., during a pre-sintering step) to provide a metal oxide that acts as a sintering inhibitor.

[0054] By "pre-colored" multi-layer dental mill blank is meant a multi-layer dental mill blank comprising an amount and / or combination of colored metal oxides effective to impart a color (e.g., a color that matches the natural color of teeth and / or matches the color of teeth using the VITA Classic A1-D4® color guide with the VITA bleaching scale manufactured by Vita Zahnfabrik or a similar tooth color guide system) to a dental restoration (or at least a portion thereof) that is machined from the mill blank and then fully sintered.

[0055] When the term "comprising" is used herein, the presence of other unspecified elements is not excluded. When the term "consisting essentially of ... " is used herein, the presence of other unspecified elements that do not have a substantial impact on the basic characteristics of the defined subject matter is not excluded. When the term "consisting essentially of ... " is used herein, the presence of other unspecified elements is not excluded. When the term "consisting essentially of ... " is used herein, the presence of other unspecified elements is excluded, but when defining the composition, it does not exclude the presence of unavoidable components, such as unavoidable trace impurities (e.g., SiO2, CaO, TiO2 or Na2O) with a total amount <0.1% by weight. For the purposes of the present invention, the terms "consisting essentially of ... " and "consisting of ... " are considered to be specific embodiments of the term "comprising ... ". Whenever the terms "including" or "having" are used, these terms are meant to be equivalent to "comprising" as defined above.

[0056] The term "obtaining" does not necessarily mean to indicate that, for example, an embodiment must be obtained through, for example, a series of steps following the term "obtaining", even though such a limited understanding is always included in the term "obtaining" as a preferred embodiment.

[0057] When a layer is described herein as comprising or having a weight content of a component, the weight content of the component is based on the total weight of the corresponding layer (unless explicitly stated otherwise). In addition, when a pre-sintered multi-layer dental mill blank is described herein as comprising or having a weight content of a component, the weight content of the component is based on the total weight of the pre-sintered multi-layer dental mill blank (unless explicitly stated otherwise). In addition, when a pre-sintered multi-layer dental mill blank or one of its layers is described herein as comprising a specific weight amount of a metal or metal cation, and the metal or metal ion is not defined as a metal oxide, it should be understood that the weight amount of the metal or metal cation is calculated based on the (most abundant) oxide of the metal or metal anion.

[0058] Numbers defined herein are rounded to the last digit and are meant to encompass ranges of rounded values ​​according to established rounding rules. For example, a value of 3 is meant to encompass values ​​within the range of 2.5 to 3.4, a value of 1.5 is meant to encompass values ​​within the range of 1.46 to 1.54, and so on. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 A graphical representation of the contrast values ​​for layers L1 to L4 provided in Tables 8A and 8B of the Examples section is shown.

[0060] Figure 2 Shown is a graphical representation of the CIE L* values ​​for layers L1 to L4 provided in Tables 8A and 8B of the Examples section.

[0061] Figure 3 The left side shows a test cross section of a dental mill blank according to mill blank No. 7, which was completely sintered by the rapid sintering method according to Table 5. On the right side, a test cross section of a dental mill blank according to a comparative example is shown, which was completely sintered by the rapid sintering method according to Table 5. The top layer L4 of each cross section is located in the upper part of the image, and the bottom layer L1 is located in the lower part of the image.

[0062] Figure 4 Shows Figure 3 An overview of the microstructure of the middle layer L3 of the fully sintered test cross section of milled blank No. 7 is shown.

[0063] Figure 5 Shown at a higher magnification Figure 4 part of the surface.

[0064] Figure 6 Shows the Figure 3 A region of interest (ROI) selected in a portion of the surface of the top layer L4 of the fully sintered test cross section of milled blank No. 7 is shown.

[0065] Figure 7 Shows Figure 3 Microstructural overview of the middle layer L3 of a fully sintered test cross section of a comparative milled blank is shown.

[0066] Figure 8 Shown at a higher magnification Figure 7 part of the surface.

[0067] Figure 9 Shows the Figure 3 A region of interest (ROI) is shown selected in a portion of the surface of the top layer L4 of a fully sintered test cross section of a comparative milled blank.

[0068] Figure 10 Shown are sintering curves for pristine 5 mol % yttria-stabilized zirconia material ("undoped"; far right) compared to sintering curves for 5 mol % yttria-stabilized zirconia materials containing varying weight amounts of zinc oxide or gallium oxide as sintering activators.

[0069] Figure 11 Shown are the sintering curves of a pristine 3 mol % yttria-stabilized zirconia material (“3Y”; right) compared to the sintering curves of a 3 mol % yttria-stabilized zirconia material containing a colorant and zinc oxide as a sintering activator (“3Y Colored and Doped with ZnO”; left), and the sintering curves of a 3 mol % yttria-stabilized zirconia material containing a colorant, zinc oxide as a sintering activator, and type II yttria as a sintering inhibitor (“3Y Colored and Doped with ZnO / Y2O3”; center).

[0070] Figure 12 Sintering curves for a raw 3 mol% yttria-stabilized zirconia material ("3Y Undoped"; left dashed line), a raw 4 mol% yttria-stabilized zirconia material ("4Y Undoped"; middle dashed line), and a raw 5 mol% yttria-stabilized zirconia material ("5Y Undoped"; right dashed line) are shown. The sintering curves are compared to the sintering curves for a material containing a colorant (A3.5 color), zinc oxide as a sintering activator, and optionally type II yttria as a sintering inhibitor. Figure 12 Modulation of the sintering kinetics after doping the material with sintering activators and sintering inhibitors, for example by shifting the sintering curve to lower temperatures, is shown. DETAILED DESCRIPTION

[0071] I. Pre-sintered multi-layer dental milling blanks

[0072] One aspect of the present invention provides a pre-sintered multi-layer dental mill blank comprising a top layer, a bottom layer, and at least one intermediate layer. The pre-sintered multi-layer dental mill blank can be further defined by the properties of a representative test cross-section sintered by a rapid sintering method, its composition, its form, structure, and / or layering.

[0073] 1. Properties of a representative test section when fully sintered by the rapid sintering method

[0074] The pre-sintered multi-layer dental mill blank according to the present invention can be characterized by providing a representative test cross-section of each layer. The representative test cross-section can have specific characteristics, such as contrast, CIE L*a*b* values, porosity, and / or mechanical properties, when fully sintered by a rapid sintering method.

[0075] 1.1 Representative test sections

[0076] The pre-sintered multi-layer dental mill blank according to the present invention can be characterized by providing a representative test cross-section of each layer. The representative test cross-section can be fully sintered by a rapid sintering method to provide a fully sintered representative test cross-section having one or more specific characteristics. The fully sintered representative test cross-section can be obtained by preparing a representative test cross-section of each layer from the pre-sintered multi-layer dental mill blank by a subtractive process (e.g., cutting, grinding, sawing), and then fully sintering the representative test cross-section by a rapid sintering method to provide the fully sintered representative test cross-section.

[0077] There are different options for preparing a representative test section for each layer. A representative test section can be cut (e.g., using a precision saw) from each of the layers of the pre-sintered multilayer dental mill blank. For example, the representative test section can be cut substantially parallel to the adjacent layers and cut in a substantially planar form. As described herein, such individually cut representative test sections of each layer can be used when determining contrast and / or CIEL*a*b* values. Therefore, in certain embodiments of the present invention, the pre-sintered multilayer dental mill blank is characterized in that a representative test section is provided for each layer, each of the representative test sections being prepared (e.g., cut) from a corresponding one of the layers of the pre-sintered multilayer dental mill blank. In certain embodiments of the present invention, the pre-sintered multilayer dental mill blank is characterized in that a representative test section is provided for each layer, each of the representative test sections being cut from a corresponding one of the layers of the pre-sintered multilayer dental mill blank, and each of the representative test sections having a substantially planar form and being cut substantially parallel to the adjacent layers.

[0078] As an alternative to cutting a test section for each layer individually, it is possible to obtain a representative test section for each layer by preparing (e.g., cutting) a cross section from a pre-sintered multi-layer dental mill blank containing all layers. As described herein, a representative test section for each layer in cross-sectional form can be used to determine the number of pores per grain. Therefore, in certain embodiments of the present invention, the pre-sintered multi-layer dental mill blank is characterized in that a representative test section for each layer is provided, the representative test section being prepared (e.g., cut) in the form of a cross section of a pre-sintered multi-layer dental mill blank having all layers. In certain embodiments of the present invention, the pre-sintered multi-layer dental mill blank is characterized in that a representative test section for each layer is provided, the representative test section being prepared (e.g., cut) in the form of a cross section of a pre-sintered multi-layer dental mill blank having all layers, and the cross section having a substantially planar form and being cut substantially perpendicular to the outer surface of the top layer.

[0079] The representative cross section can be prepared from a portion of the pre-sintered dental mill blank that is at least 1 mm away from the outer surface of the pre-sintered dental mill blank. Thus, potential unavoidable surface defects or unavoidable defects close to the surface of the mill blank may not be part of the representative test cross section. Before being fully sintered by the rapid sintering method, the representative test cross section can be processed, for example, ground and / or polished. Before being subjected to the measurement method, the fully sintered representative test cross section can be processed (e.g., ground and / or polished) to a specific thickness.

[0080] When a specific thickness (e.g., a thickness of 0.8 mm) is defined herein for measuring a characteristic of a fully sintered representative test section (e.g., contrast or CIE L*a*b* value), this is not to be understood as meaning that each layer of the layers of the pre-sintered dental mill blank must have a minimum thickness of the specific thickness (although this is possible). If the layers of a pre-sintered multi-layer dental mill blank are not thick enough to prepare a fully sintered representative test section having a specific thickness (e.g., a thickness of 0.8 mm), a fully sintered representative test section of the layers can be prepared from a similar pre-sintered multi-layer dental mill blank containing layers of the same composition but having sufficient thickness. Similarly, when a characteristic of a fully sintered representative test section (e.g., flexural strength or fracture toughness) is to be measured following a specific measurement method, such as a standardized measurement method (e.g., ISO specification or ASTM specification, etc.), this is not to be understood as meaning that the corresponding layers of the pre-sintered dental mill blank must have the specimen size required to perform the specific measurement method (although this is possible). If the layers of a pre-sintered multilayer dental mill blank do not have sufficient specimen size for a particular measurement method, a fully sintered representative test cross-section of the layers can be prepared from a similar pre-sintered multilayer dental mill blank comprising layers of the same composition but of sufficient size.

[0081] 1.2 Rapid sintering method

[0082] The fast sintering method as defined herein may be a sintering method having a total duration of less than 25 minutes or less than 20 minutes, such as in the range of 12 minutes to 25 minutes or 12 minutes to 20 minutes (e.g., 14 minutes, 15 minutes, or 16 minutes) and having a maximum sintering temperature of at least 1350°C, at least 1400°C, at most 1650°C, or at most 1600°C or at most 1500°C, such as in the range of 1350°C to 1650°C or 1400°C to 1600°C (e.g., 1450°C or 1560°C) or 1400°C to 1500°C. In one embodiment, the fast sintering method is a sintering method having a total duration of less than 20 minutes and having a maximum sintering temperature in the range of 1400°C to 1500°C. For example, the fast sintering method may be a sintering method having a total duration in the range of 12 minutes to 20 minutes and a maximum sintering temperature of 1450°C. A suitable sintering furnace for carrying out this sintering method is the Programat CS6 sintering furnace, which is commercially available from Ivoclar Vivadent AG.

[0083] A flash sintering method as defined herein may be a sintering method consisting of the following steps:

[0084] - a first heating step starting from 25 °C at a heating rate of 200 K / min and ending at 1050 °C,

[0085] - a second heating step starting at 1050 °C and ending at 1450 °C at a heating rate of 100 K / min,

[0086] - a hold step where the temperature is kept at 1450°C for 2 minutes,

[0087] - a first cooling step starting from 1450°C and ending at 1350°C at a cooling rate of 130 K / min,

[0088] - a second cooling step starting from 1350°C and ending at 1200°C at a cooling rate of 70 K / min, followed by cooling, and

[0089] wherein the first heating step and the second heating step are performed by applying a vacuum at a pressure in the range of 50 mbar to 100 mbar (e.g. 80 mbar) until a temperature of 1400°C is reached, and once the temperature of 1400°C is reached, the vacuum is exchanged with air.

[0090] A fast sintering process as defined herein may be a sintering process as described in Table 5. Cooling, which is not considered part of the sintering process, may be completed in less than 10 minutes, such as less than 5 minutes, or less than 3 minutes (e.g., when a temperature of 400°C is reached).

[0091] 1.3 Contrast

[0092] One embodiment of the present invention provides a pre-sintered multi-layer dental mill blank comprising

[0093] Top floor,

[0094] bottom layer, and

[0095] At least one intermediate layer,

[0096] The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer having increasing contrast from the top layer to the bottom layer when fully sintered by a rapid sintering process.

[0097] The contrast can increase from the top layer to the bottom layer, such that the contrast of the top layer is lower than the contrast of at least one intermediate layer, and the contrast of at least one intermediate layer is also lower than the contrast of the bottom layer. In one embodiment, the pre-sintered multi-layer dental mill blank comprises a plurality of intermediate layers, wherein the contrast does not increase layer by layer for each intermediate layer in a direction from the top layer to the bottom layer. However, it is preferred that the contrast of each layer increases layer by layer from the top layer to the bottom layer.

[0098] One embodiment of the present invention provides a pre-sintered multi-layer dental mill blank comprising

[0099] Top floor,

[0100] bottom layer, and

[0101] At least one intermediate layer,

[0102] The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer having increasing contrast from the top layer to the bottom layer when fully sintered by a rapid sintering process.

[0103] When the contrast increases layer by layer as described herein, the pre-sintered multi-layer dental mill blank is suitable for preparing dental restorations having a natural and highly aesthetic appearance by a rapid sintering process. For example, the mill blank can be used to prepare a dental restoration having increased translucency from its bottom portion (e.g., a portion of the dentin area of ​​the restoration) to its top portion (e.g., a portion of the incision area of ​​the restoration) by a rapid sintering step.

[0104] The representative test cross-sections are fully sintered using a rapid sintering method to obtain fully sintered representative test cross-sections, each having a specific contrast. The contrast increases from the fully sintered representative test cross-section of the top layer to the fully sintered representative test cross-section of the bottom layer, preferably layer by layer. For example, when the pre-sintered multi-layer dental mill blank comprises a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1, the contrast preferably increases layer by layer from the fully sintered representative test cross-section of the top layer L4, to the fully sintered representative test cross-section of the intermediate layer L3, to the fully sintered representative test cross-section of the intermediate layer L2, and finally to the fully sintered representative test cross-section of the bottom layer L1.

[0105] Unless otherwise expressly stated, contrast as defined herein refers to the contrast of a representative test cross-section fully sintered by the rapid sintering method. Contrast may allow for tolerances due to unavoidable manufacturing variability and / or measurement deviations of approximately ±1.0% or less.

[0106] The contrast of a fully sintered representative test section generally depends on the thickness of the fully sintered representative test section, with an increase in thickness resulting in an increase in contrast. Therefore, the contrast of a fully sintered representative test section will be determined on a test section with the same or substantially the same thickness. Unless expressly stated otherwise, contrast as defined herein preferably refers to the contrast determined for a fully sintered representative test section with a thickness of 0.8 mm, and in particular a thickness of 0.80 ± 0.02 mm. Contrast can be determined according to BS 5612, in particular BS 5612:1978. A suitable device for measuring contrast is, for example, a spectrophotometer CM 3700-D (Konica-Minolta).

[0107] The contrast ratio [%] of each layer may be at least 56%, at least 61%, at least 62%, or at least 64%. The contrast ratio [%] of each layer may be at most 88%, at most 83%, at most 82%, or at most 79%. The contrast ratio [%] of each layer may be in the range of 56% to 88%, 61% to 83%, 62% to 82%, or 64% to 79%. In one embodiment, the contrast ratio [%] of each layer is in the range of 61% to 83%.

[0108] The contrast ratios of the layers may differ by percentage points of a specific value. The contrast ratio [%] of the bottom layer may differ from the contrast ratio [%] of the top layer by at least 2 percentage points, at least 3 percentage points, at least 5 percentage points, at least 8 percentage points, or at least 10 percentage points. The contrast ratio [%] of the bottom layer may differ from the contrast ratio [%] of the top layer by up to 24 percentage points, up to 22 percentage points, up to 19 percentage points, up to 18 percentage points, or up to 16 percentage points. The contrast ratio [%] of the bottom layer may differ from the contrast ratio [%] of the top layer by 2 to 24 percentage points, 3 to 22 percentage points, 5 to 19 percentage points, 8 to 18 percentage points, or 10 to 16 percentage points. In one embodiment, the contrast ratio [%] of the bottom layer differs from the contrast ratio [%] of the top layer by at least 5 percentage points, such as 5 to 19 percentage points.

[0109] The contrast ratio of the top layer and the contrast ratio of the bottom layer may satisfy the following formula (I), (II), (III) or (IV):

[0110] CR(TL) / CR(BL) ≥ 75.0% (I),

[0111] CR(TL) / CR(BL) ≥ 77.0% (II),

[0112] CR(TL) / CR(BL) ≥ 82.0% (III),

[0113] CR(TL) / CR(BL) ≥ 85.0% (IV),

[0114] Where CR(TL) is the contrast of the top layer [%], and CR(BL) is the contrast of the bottom layer [%].

[0115] The contrast ratio of the bottom layer can be at least 66%, at least 70%, at least 71%, or at least 74%. The contrast ratio of the bottom layer can be at most 88%, at most 83%, at most 81%, or at most 80%. The contrast ratio of the bottom layer can be in the range of 66% to 88%, 70% to 83%, 71% to 81%, or 74% to 80%. In one embodiment, the contrast ratio of the bottom layer is in the range of 70% to 83%.

[0116] The contrast ratio of the top layer can be at least 56%, at least 61%, at least 62%, or at least 64%. The contrast ratio of the top layer can be at most 72%, at most 68%, at most 67%, or at most 66%. The contrast ratio of the top layer can be in the range of 56% to 72%, 61% to 68%, 62% to 67%, or 64% to 66%. In one embodiment, the contrast ratio of the top layer is in the range of 61% to 68%.

[0117] The contrast ratio of the at least one intermediate layer may be at least 62%, at least 66%, at least 67%, or at least 68%. The contrast ratio of the at least one intermediate layer may be at most 83%, at most 79%, at most 78%, or at most 76%. The contrast ratio of the at least one intermediate layer may be in the range of 62% to 83%, 66% to 79%, 67% to 78%, or in the range of 68% to 76%.

[0118] The contrast ratio [%] of each pair of adjacent layers may differ by at least 0.3 percentage points, at least 0.5 percentage points, at least 1.0 percentage points, at least 1.5 percentage points, at least 2.0 percentage points, at least 2.5 percentage points, at least 3.0 percentage points, or at least 3.5 percentage points. The contrast ratio [%] of each pair of adjacent layers may differ by, for example, up to 7.0 percentage points or up to 6.0 percentage points. The contrast ratio [%] of each pair of adjacent layers may differ by 0.3 percentage points to 7.0 percentage points, 0.5 percentage points to 7.0 percentage points, 1.0 percentage points to 7.0 percentage points, 1.5 percentage points to 7.0 percentage points, 2.0 percentage points to 6.0 percentage points, 2.5 percentage points to 6.0 percentage points, or 3.0 percentage points to 6.0 percentage points. In one embodiment, the contrast ratio [%] of each pair of adjacent layers differs by at least 2.0 percentage points, such as 2.0 percentage points to 6.0 percentage points.

[0119] The contrast ratio of the intermediate layer adjacent to the top layer can be at least 62%, at least 66%, or at least 67%. The contrast ratio of the intermediate layer adjacent to the top layer can be at most 74%, at most 72%, at most 71%, or at most 70%. The contrast ratio of the intermediate layer adjacent to the top layer can be in the range of 63% to 74%, 66% to 72%, 67% to 71%, or 67% to 70%. The contrast ratio [%] of the intermediate layer adjacent to the top layer can differ from the contrast ratio of the top layer by 0.2 percentage points to 9.0 percentage points, 0.5 percentage points to 7.0 percentage points, 1.0 percentage points to 6.0 percentage points, or 1.5 percentage points to 5.0 percentage points.

[0120] The contrast ratio of the intermediate layer adjacent to the bottom layer can be at least 64%, at least 68%, at least 69%, or at least 70%. The contrast ratio of the intermediate layer adjacent to the bottom layer can be at most 82%, at most 79%, at most 78%, or at most 77%. The contrast ratio of the intermediate layer adjacent to the bottom layer can be in the range of 64% to 82%, 68% to 79%, 69% to 78%, or 70% to 77%. The contrast ratio [%] of the intermediate layer adjacent to the bottom layer can differ from the contrast ratio of the bottom layer by 0.5 percentage points to 12.0 percentage points, 1.5 percentage points to 7.0 percentage points, 2.0 percentage points to 5.5 percentage points, or 3.0 percentage points to 4.5 percentage points.

[0121] The pre-sintered multi-layer dental mill blank may comprise at least two intermediate layers, and the contrast [%] of one intermediate layer may differ from the contrast of the other intermediate layer by at least 0.2 percentage points, at least 0.5 percentage points, at least 3.0 percentage points, or at least 4.0 percentage points, and / or at most 12 percentage points, at most 10.0 percentage points, at most 9.0 percentage points, or at most 8.0 percentage points. The pre-sintered multi-layer dental mill blank may comprise at least two intermediate layers, and the contrast [%] of one intermediate layer may differ from the contrast of the other intermediate layer by 0.2 percentage points to 12 percentage points, 0.5 percentage points to 10.0 percentage points, 3.0 percentage points to 9.0 percentage points, or 4.0 percentage points to 8.0 percentage points.

[0122] The pre-sintered multi-layer dental mill blank may comprise the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, and the contrast of the layers satisfies one or more of the contrast profiles A1.1 to J1.1 as defined in Table A1 herein. This set of contrast profiles A1.1 to J1.1 (or A1.2 to J1.2) is advantageous because it provides a suitable choice of aesthetic appearance that matches the appearance of natural teeth (e.g., in terms of translucency) for most patients. The set of contrast profiles C1.1 to H1.1 (or C1.2 to H1.2) (e.g., F1.1 or G1.1 (or F1.2 or G1.2)) may be considered particularly advantageous because it provides a suitable choice of aesthetic appearance that matches the appearance of natural teeth (e.g., in terms of translucency) for a large subset of all patients.

[0123] Table A1:

[0124]

[0125] The pre-sintered multilayer dental mill blank may comprise the following layers: top layer L4, middle layer L3, middle layer L2, bottom layer L1, and the contrast of the layers satisfies one or more of contrast distributions A1.2 to J1.2 as defined in Table A2 herein.

[0126] Table A2:

[0127]

[0128] In one embodiment, the pre-sintered multi-layer dental mill blank consists of the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, and the contrast of the layers satisfies one or more of the contrast profiles a.1.1 to J1.1 as defined in Table A1 herein or A1.2 to J1.2 as defined in Table A2 herein. In one embodiment, the pre-sintered multi-layer dental mill blank consists of the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, and the contrast of the layers satisfies one or more of the contrast profiles C1.1 to H1.1 as defined in Table A1 herein (e.g., profiles F1.1 or G1.1) or C1.2 to H1.2 as defined in Table A2 herein (e.g., F1.2 or G1.2).

[0129] In addition to or as an alternative to the contrast ratio as described herein, the representative test cross-sections may have other characteristics as described herein, such as CIE L*a*b values, number of pores per grain, or mechanical properties when fully sintered by the rapid sintering method.

[0130] 1.4 CIE L*a*b* values

[0131] One embodiment of the present invention provides a pre-sintered multi-layer dental mill blank comprising

[0132] Top floor,

[0133] bottom layer, and

[0134] At least one intermediate layer,

[0135] The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer having a CIE lightness L* that increases from the bottom layer to the top layer when fully sintered by a rapid sintering process.

[0136] The CIE brightness L* can increase from the bottom layer to the top layer, such that the CIE brightness L* of the bottom layer is lower than the CIE brightness L* of at least one intermediate layer, and the CIE brightness L* of at least one intermediate layer is lower than the CIE brightness L* of the bottom layer. In one embodiment, the pre-sintered multi-layer dental mill blank comprises a plurality of intermediate layers, wherein the CIE brightness L* does not increase layer by layer for each intermediate layer in the direction from the bottom layer to the top layer. However, it is preferred that the CIE brightness L* of each layer increases layer by layer from the bottom layer to the top layer.

[0137] One embodiment of the present invention provides a pre-sintered multi-layer dental mill blank comprising

[0138] Top floor,

[0139] bottom layer, and

[0140] At least one intermediate layer,

[0141] The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer having a CIE lightness L* that increases from the bottom layer to the top layer when fully sintered by a rapid sintering process.

[0142] When the CIE lightness L* increases layer by layer as described herein, the pre-sintered multi-layer dental mill blank is suitable for preparing a dental restoration having desired optical properties (e.g., a natural and aesthetic appearance) by a rapid sintering process. For example, the mill blank may be suitable for preparing a dental restoration having a more uniform color transition from its bottom portion (e.g., a portion of the dentin area of ​​the restoration) to its top portion (e.g., a portion of the cutout area of ​​the restoration) by a rapid sintering step.

[0143] The representative test sections are fully sintered using a rapid sintering method to obtain fully sintered representative test sections, each having a CIE L*a*b* value. The CIE lightness L* increases from the fully sintered representative test section of the bottom layer to the fully sintered representative test section of the top layer, preferably increasing layer by layer. For example, when the pre-sintered multi-layer dental mill blank comprises a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1, the CIE lightness L* preferably increases layer by layer from the fully sintered representative test section of the bottom layer L1, to the fully sintered representative test section of the intermediate layer L2, to the fully sintered representative test section of the intermediate layer L3, and finally to the fully sintered representative test section of the top layer L4.

[0144] Unless otherwise expressly stated, the CIE L*a*b* values ​​defined herein refer to the CIE L*a*b* values ​​of a representative test section fully sintered by the rapid sintering method. Due to unavoidable manufacturing variability and / or measurement deviations of approximately ±0.5, CIE lightness L* (and optionally CIE a* and b* values) may allow for tolerances.

[0145] The CIE L*a*b* value of a fully sintered representative test section generally depends on its thickness. Therefore, the CIE L*a*b* value of a fully sintered representative test section will be determined on a test section with the same or substantially the same thickness. Unless otherwise expressly stated, the CIE L*a*b* value as defined herein preferably refers to the CIE L*a*b* value determined for a fully sintered representative test section with a thickness of 0.8 mm, and in particular 0.80 ± 0.02 mm. The CIEL*a*b* value can be measured according to DIN 6174. Spectrophotometer CM 3700-D (Konica-Minolta) can be used for measurement. Measured can be performed for a background of, for example, L* = 93.1; a* = (-0.64); b* = 4.22.

[0146] The CIE lightness L* of each layer may be at least 72, at least 76, at least 78, or at least 79. The CIE lightness L* of each layer may be at most 98, at most 94, at most 92, or at most 91. The CIE lightness L* of each layer may be in the range of 72 to 98, 76 to 94, 78 to 92, or 79 to 91. In one embodiment, the CIE lightness L* of each layer is in the range of 78 to 92.

[0147] The CIE lightness L* of each pair of two adjacent layers may differ by at least 0.05, at least 0.4, at least 0.6, or at least 0.8. The CIE lightness L* of each pair of two adjacent layers may differ by at most 3.0, at most 2.5, or at most 2.0. The CIE lightness L* of each pair of two adjacent layers may differ by a value in the range of 0.05 to 3.0, 0.4 to 3.0, 0.6 to 2.5, or 0.8 to 2.0. In one embodiment, the CIE lightness L* of each pair of two adjacent layers may differ by at least 0.6, such as in the range of 0.6 to 2.5 or 0.6 to 2.0.

[0148] The CIE lightness L* of the bottom layer may be at least 72, at least 76, at least 78, at least 80, at least 82, or at least 84. The CIE lightness L* of the bottom layer may be at most 94, at most 92, at most 90, at most 88, at most 86, or at most 84. The CIE lightness L* of the bottom layer may be in the range of 72 to 94, 76 to 92, 78 to 90, 80 to 88, or 80 to 86. In one embodiment, the CIE lightness L* of the bottom layer is in the range of 76 to 92.

[0149] The CIE lightness L* of the top layer may be at least 80, at least 84, at least 86, at least 88, or at least 90. The CIE lightness L* of the top layer may be at most 98, at most 96, at most 94, at most 92, or at most 90. The CIE lightness L* of the top layer may be in the range of 80 to 98, 84 to 94, 86 to 92, or 86 to 90. In one embodiment, the CIE lightness L* of the top layer is in the range of 84 to 94. The CIE lightness L* of the top layer may be at least 0.5, at least 1.0, at least 2.0, at least 3.0, or at least 4.0 higher than the CIE lightness L* of the bottom layer. The CIE lightness L* of the top layer may be at most 12, at most 10, at most 9.0, at most 8.0, or at most 7.0 higher than the CIE lightness L* of the bottom layer. The CIE lightness L* of the top layer may be higher than the CIE lightness of the bottom layer by a value in the range of 0.5 to 12, 1.0 to 10, 2.0 to 9.0, 2.0 to 8.0, or 2.0 to 7.0. In one embodiment, the CIE lightness L* of the top layer is higher than the CIE lightness of the bottom layer by a value in the range of 2.0 to 9.0.

[0150] The CIE a* value of each layer may be at least -3.5, at least -2.2, at least -1.8, or at least 1.0. The CIE a* value of each layer may be at most 7.5, at most 6.5, at most 5.6, or at most 5.0. The CIE a* value of each layer may be in the range of -3.5 to 7.5, -2.2 to 6.6, -1.8 to 5.6, or -1.0 to 5.0. In one embodiment, the CIE a* value of each layer is in the range of -2.2 to 6.5.

[0151] In one embodiment, when fully sintered by a flash sintering process, a representative test cross section has CIE a* values ​​that increase from the top layer to the bottom layer.

[0152] The CIE b* value of each layer may be at least 1, at least 3, at least 4, or at least 11. The CIE b* value of each layer may be at most 30, at most 26, at most 24, or at most 22. The CIE b* value of each layer may be in the range of 1 to 30, 3 to 26, 4 to 24, or 11 to 22. In one embodiment, the CIE b* value of each layer may be in the range of 3 to 26.

[0153] Pre-sintered multi-layer dental mill blanks can contain the following layers:

[0154] Top floor L4,

[0155] Middle layer L3,

[0156] Middle layer L2,

[0157] The bottom layer L1, and

[0158] When fully sintered by the flash sintering method, the representative test cross section has a CIE lightness L* of the layer that satisfies one or more of the CIE lightness L* distributions A2.1 to J2.1 as defined in Table B1 herein.

[0159] This set of CIE lightness L* distributions A2.1 to J2.1 (or A2.2 to J2.2) (optionally in combination with other distribution sets as described herein) is advantageous because it provides a suitable choice of aesthetic appearance that matches the appearance of natural teeth (e.g., in terms of lightness) for most patients. A set of CIE lightness L* distributions C2.1 to H2.1 (or C2.2 to H2.2) (e.g., F1.1 or G1.1 (or F1.2 or G1.2)) can be considered particularly advantageous because it provides a suitable choice of aesthetic appearance that matches the appearance of natural teeth (e.g., in terms of lightness) for a large subset of all patients.

[0160] Table B1:

[0161]

[0162] Pre-sintered multi-layer dental mill blanks can contain the following layers:

[0163] Top floor L4,

[0164] Middle layer L3,

[0165] Middle layer L2,

[0166] The bottom layer L1, and

[0167] When fully sintered by the flash sintering method, the representative test cross-section has a CIE lightness L* of the layer that satisfies one or more of the CIE lightness L* distributions A2.2 to J2.2 as defined in Table B2 herein.

[0168] Table B2:

[0169]

[0170] In one embodiment, the pre-sintered multi-layer dental mill blank consists of the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, and the CIE lightness L* of the layers satisfies one or more of the CIE lightness L* distributions A.2.1 to J2.1 as defined in Table B1 herein or A2.2 to J2.2 as defined in Table B2 herein. In one embodiment, the pre-sintered multi-layer dental mill blank consists of the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, and the CIE lightness L* of the layers satisfies one or more of the CIE lightness L* distributions C2.1 to H2.1 (e.g., distributions F2.1 or G2.1) as defined in Table B1 herein or C2.2 to H2.2 (e.g., F2.2 or G2.2) as defined in Table B2 herein.

[0171] Pre-sintered multi-layer dental mill blanks can contain the following layers:

[0172] Top floor L4,

[0173] Middle layer L3,

[0174] Middle layer L2,

[0175] The bottom layer L1, and

[0176] When fully sintered by the flash sintering method, the representative test cross section has a CIE a* value that satisfies one or more of the CIE a* value distributions A3.1 to J3.1 as defined in Table C1 herein.

[0177] Table C1:

[0178]

[0179] Pre-sintered multi-layer dental mill blanks can contain the following layers:

[0180] Top floor L4,

[0181] Middle layer L3,

[0182] Middle layer L2,

[0183] The bottom layer L1, and

[0184] When fully sintered by the flash sintering method, the representative test cross-section has a CIE a* value that satisfies one or more of the CIE a* value distributions A3.2 to J3.2 as defined in Table C2 herein.

[0185] Table C2:

[0186]

[0187] In one embodiment, the pre-sintered multi-layer dental mill blank consists of the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, and the CIE a* values ​​of the layers satisfy one or more of the CIE a* value distributions A3.1 to J3.1 as defined in Table C1 herein or A3.2 to J3.2 as defined in Table C2 herein.

[0188] Pre-sintered multi-layer dental mill blanks can contain the following layers:

[0189] Top floor L4,

[0190] Middle layer L3,

[0191] Middle layer L2,

[0192] The bottom layer L1, and

[0193] When fully sintered by the flash sintering method, the representative test cross section has a CIE b* value that satisfies one or more of the CIE b* value distributions A4.1 to J4.1 as defined in Table D1 herein.

[0194] Table D1:

[0195]

[0196] Pre-sintered multi-layer dental mill blanks can contain the following layers:

[0197] Top floor L4,

[0198] Middle layer L3,

[0199] Middle layer L2,

[0200] The bottom layer L1, and

[0201] When fully sintered by the flash sintering method, the representative test cross section has a CIE b* value, and the CIE b* value range of the layer satisfies one or more of the CIE b* value distributions A4.2 to J4.2 in Table D2.

[0202] Table D2:

[0203]

[0204] In one embodiment, the pre-sintered multi-layer dental mill blank consists of the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, and the CIE b* values ​​of the layers satisfy one or more of the CIE b* value distributions A4.1 to J4.1 as defined in Table D1 herein or A4.2 to J4.2 as defined in Table D2 herein.

[0205] The CIE L*a*b* values ​​of the layers may satisfy a specific combination of CIE L*a*b* value distributions as defined herein. The pre-sintered multi-layer dental mill blank may comprise the following layers:

[0206] Top floor L4,

[0207] Middle layer L3,

[0208] Middle layer L2,

[0209] The bottom layer L1, and

[0210] When fully sintered by the flash sintering method, the representative test cross section has CIE L*a*b* values, and the CIEL*a**b* values ​​of the layer meet one or more of the optical property distributions a to j as defined in Table El herein.

[0211] Table E1:

[0212]

[0213] The CIE lightness L* distributions A2.1 to J2.1, the CIE a* value distributions A3.1 to J3.1, and the CIE b* value distributions A4.1 to J4.1 are as defined in Tables B1 to D1 herein.

[0214] Pre-sintered multi-layer dental mill blanks can contain the following layers:

[0215] Top floor L4,

[0216] Middle layer L3,

[0217] Middle layer L2,

[0218] The bottom layer L1, and

[0219] When fully sintered by the flash sintering method, the representative test cross section has CIE L*a*b* values, and the CIEL*a**b* values ​​of the layer meet one or more of the optical property distributions aa to jj as defined in Table E2 herein.

[0220] Table E2:

[0221]

[0222] The CIE lightness L* distribution is A2.2 to J2.2, the CIE a* value distribution is A3.2 to J3.2, and the CIE b* value distribution is A4.2 to J4.2 as defined in Tables B2 to D2 herein.

[0223] Pre-sintered multi-layer dental mill blanks can contain the following layers:

[0224] Top floor L4,

[0225] Middle layer L3,

[0226] Middle layer L2,

[0227] The bottom layer L1, and

[0228] When fully sintered by the flash sintering method, the representative test cross section has CIE L*a*b* values ​​and contrast ratios, and the CIE L*a*a*b** values ​​and contrast ratios of the layer satisfy one or more of the optical property distributions A to J in Table F1.

[0229] This set of optical property profiles A to J (or Aa to Jj) is advantageous because it provides a suitable selection of aesthetic appearance that matches the appearance of natural teeth (e.g., in terms of translucency and color) for most patients. The set of optical property profiles C to H (or Cc to Hh) (e.g., F or G (or Ff or Gg)) can be considered particularly advantageous because it provides a suitable selection of aesthetic appearance that matches the appearance of natural teeth (e.g., in terms of translucency and color) for a large subset of all patients.

[0230] Table F1:

[0231]

[0232] Contrast distributions A1.1 to J1.1, CIE lightness L* distributions A2.1 to J2.1, CIE a* value distributions A3.1 to J3.1, and CIE b* value distributions A4.1 to J4.1 are as defined in Tables A1 to D1 herein.

[0233] Pre-sintered multi-layer dental mill blanks can contain the following layers:

[0234] Top floor L4,

[0235] Middle layer L3,

[0236] Middle layer L2,

[0237] The bottom layer L1, and

[0238] When fully sintered by the flash sintering method, the representative test cross section has CIE L*a*b* values ​​and contrast ratios, and the CIE L*a*a*b** values ​​and contrast ratios of the layer satisfy one or more of the optical property distributions Aa to Jj in Table F2.

[0239] Table F2:

[0240]

[0241] Contrast ratio distributions A1.2 to J1.2, CIE lightness L* distributions A2.2 to J2.2, CIE a* value distributions A3.2 to J3.2, and CIE b* value distributions A4.2 to J4.2 are as defined in Tables A2 to D2 herein.

[0242] In one embodiment, the pre-sintered multi-layer dental mill blank consists of the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, and the CIE L*a*b* values ​​and contrast ratios of the layers satisfy one or more of the optical property distributions A to J as defined in Table F1 herein or Aa to Jj as defined in Table F2 herein. In one embodiment, the pre-sintered multi-layer dental mill blank consists of the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, and the CIE L*a*b* values ​​and contrast ratios of the layers satisfy one or more of the optical property distributions C to H (e.g., F or G) as defined in Table F1 herein or Cc to Hh (e.g., Ff or Gg) as defined in Table F2 herein.

[0243] In addition to or instead of the CIE L*a*b values ​​as described herein, the representative test cross-sections may have other characteristics as described herein, such as contrast, number of pores per grain, or mechanical properties, when fully sintered by the rapid sintering method.

[0244] 1.5 Number of holes per grain

[0245] One embodiment of the present invention provides a pre-sintered multi-layer dental mill blank comprising

[0246] Top floor,

[0247] bottom layer, and

[0248] At least one intermediate layer,

[0249] each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer,

[0250] The pre-sintered multilayer dental mill blank is characterized by providing a representative test cross-section of each layer, and when fully sintered by a rapid sintering method, a representative test cross-section of the top layer and / or an intermediate layer adjacent to the top layer has a pore count per grain of less than 0.25.

[0251] The yttrium oxide content of the layers can increase from the bottom layer to the top layer, such that the bottom layer has a lower yttrium oxide content than at least one intermediate layer, and at least one intermediate layer has a lower yttrium oxide content than the top layer. In one embodiment, the pre-sintered multi-layer dental mill blank comprises a plurality of intermediate layers, wherein not every intermediate layer has an increasing yttrium oxide content from the bottom layer to the top layer. However, preferably, the yttrium oxide content of each layer increases from the bottom layer to the top layer.

[0252] One embodiment of the present invention provides a pre-sintered multi-layer dental mill blank comprising

[0253] Top floor,

[0254] bottom layer, and

[0255] At least one intermediate layer,

[0256] Each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer,

[0257] The pre-sintered multilayer dental mill blank is characterized by providing a representative test cross-section of each layer, and when fully sintered by a rapid sintering method, a representative test cross-section of the top layer and / or an intermediate layer adjacent to the top layer has a pore count per grain of less than 0.25.

[0258] In one embodiment, a representative tested cross-section of the top layer has a pore count per grain of less than 0.25 when fully sintered by a rapid sintering process. In one embodiment, a representative tested cross-section of an intermediate layer adjacent to the top layer has a pore count per grain of less than 0.25 when fully sintered by a rapid sintering process. In one embodiment, a representative tested cross-section of the top layer and the intermediate layer adjacent to the top layer has a pore count per grain of less than 0.25 when fully sintered by a rapid sintering process.

[0259] The representative test section of the top layer and / or the intermediate layer adjacent to the top layer is fully sintered by a rapid sintering method to provide a fully sintered representative test section of the top layer and / or a fully sintered representative test section of the intermediate layer adjacent to the top layer, the fully sintered representative test section having a number of pores per grain as defined herein.

[0260] When the number of pores per grain is low as defined herein, the pre-sintered multilayer dental mill blank is suitable for preparing dental restorations having desired optical properties by a rapid sintering process. In particular, the mill blank may be suitable for preparing dental restorations having a more translucent cutout or occlusal area (particularly the portion of the cutout area prepared from the top layer) which is highly desirable from an aesthetic point of view by a rapid sintering process. Without wishing to be bound by theory, it is believed that residual pores in a fully sintered dental restoration (e.g., Figures 7 to 9Those pores visible in the nanostructured material may diffract or scatter light in an undesirable manner and may therefore be detrimental to the optical properties of the fully sintered dental restoration, such as its translucency.

[0261] As used herein, the number of "pores" per particle refers to the number of pores with a diameter in the range of 2 nm to 1000 nm. Pores can be interparticle pores or intraparticle pores. "Interparticle pores" refer to pores located between two or more different particles, such as pores located at the boundary of two or more different particles. "Intraparticle pores" refer to pores located within a particle.

[0262] The number of pores per grain or intragranular pores per grain is preferably determined by microstructural analysis of the surface of a fully sintered representative test section (also referred to herein as a "region of interest (ROI)") using a scanning electron microscope (SEM), as described in the "Measurement Methods" section below. The surface of a fully sintered representative test section is preferably at least 50 μm 2 , such as between 50 and 2000 µm 2 in the range (e.g., 500 to 2000 µm 2 in the range of 50 to 1500 µm 2 in the range (e.g., between 500 and 1500 µm 2 in the range of 50 to 1000 µm 2 In the range of 50 to 500 µm 2 or in the range of 50 to 300 µm 2 The surface can be selected so that the grains of the surface have a number average grain size of at least 0.7 μm, at least 1.0 μm, at least 1.2 μm (e.g., in the range of 1.2 μm to 2.5 μm or 1.2 μm to 2.2 μm), or at least 1.4 μm (e.g., in the range of 1.4 μm to 2.5 μm or 1.4 μm to 2.2 μm). The number average grain size can be determined as described in the "Measurement Methods" section below. It is believed that yttria-stabilized zirconia particles having a relatively high yttria content (e.g., in the range of 5Y-YSZ materials) grow faster during a fast sintering process (e.g., a sintering process as defined in Table 5 herein) than yttria-stabilized zirconia grains having a lower yttria content and therefore ultimately have a larger grain size after sintering. It is also possible to select several surfaces of a fully sintered representative test section (e.g. two, three, four or more surfaces with a surface area in the range of 50 to 300 µm 2 ) in order to determine the number of pores per grain (or the number of intra-grain pores per grain) for each of the surfaces, thereby calculating the number of pores per grain for the combined surface.

[0263] The top layer may have a pore count per grain of less than 0.20, less than 0.15, less than 0.10, less than 0.05, or less than 0.02. Similarly, an intermediate layer adjacent to the top layer may have a pore count per grain of less than 0.20, less than 0.15, less than 0.10, less than 0.05, or less than 0.02. In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer, and when fully sintered by a rapid sintering process, the representative test cross-section has a pore count per grain of less than 0.25, less than 0.20, less than 0.15, less than 0.10, less than 0.05, or less than 0.02.

[0264] When fully sintered by the rapid sintering method, a representative tested cross-section of the top layer and / or the intermediate layer adjacent to the top layer may have an intragranular pore count of less than 0.20, less than 0.15, less than 0.10, less than 0.05, or less than 0.02 per particle. In one embodiment, when fully sintered by the rapid sintering method, a representative tested cross-section of the top layer has an intragranular pore count of less than 0.20, less than 0.15, less than 0.10, less than 0.05, or less than 0.02 per particle. In one embodiment, when fully sintered by the rapid sintering method, a representative tested cross-section of the intermediate layer adjacent to the top layer has an intragranular pore count of less than 0.20, less than 0.15, less than 0.10, less than 0.05, or less than 0.02 per particle. In one embodiment, representative tested sections of the top layer and the intermediate layer adjacent to the top layer may have an intragranular pore count per granule of less than 0.20, less than 0.15, less than 0.10, less than 0.05, or less than 0.02 when fully sintered by a flash sintering process.

[0265] In addition to or as an alternative to the number of pores per grain as described herein, the representative test cross-sections may have other characteristics as described herein, such as CIE L*a*b values, contrast ratio, or mechanical properties when fully sintered by the rapid sintering method.

[0266] 1.6 Mechanical properties

[0267] When fully sintered by the rapid sintering method, a representative test section may be characterized by specific mechanical properties, such as flexural strength or fracture toughness. Unless expressly stated otherwise, the flexural strength and / or fracture toughness of a layer as defined herein refers to the flexural strength and fracture toughness of a representative test section of the layer fully sintered by the rapid sintering method. The flexural strength may be determined according to ISO 6872:2015. Fracture toughness (K Ic ) can be determined as described in the following section "Measurement Methods".

[0268] A representative test section may have a specific flexural strength and / or a specific fracture toughness K when fully sintered by a flash sintering method. ICThe flexural strength of the top layer may be at least 500 MPa, at least 550 MPa, at least 575 MPa, or at least 600 MPa. The flexural strength of the top layer may be at most 1100 MPa, at most 1000 MPa, at most 800 MPa, or at most 750 MPa. The flexural strength of the top layer may be in the range of 500 MPa to 1100 MPa, 550 MPa to 1000 MPa, 575 MPa to 800 MPa, or 600 MPa to 750 MPa. The fracture toughness K of the top layer IC Can be at least 2.5 MPa*m 1 / 2 , at least 2.7MPa*m 1 / 2 or at least 2.8 MPa*m 1 / 2 The fracture toughness K of the top layer IC Can be up to 3.5 MPa*m 1 / 2 , up to 3.3 MPa*m 1 / 2 or up to 3.2 MPa*m 1 / 2 The fracture toughness K of the top layer IC It can be between 2.5 and 3.5 MPa*m 1 / 2 , 2.7 to 3.3 MPa*m 1 / 2 or 2.8 to 3.2 MPa*m 1 / 2 Such strength and / or toughness is ideal so as to provide sufficient strength and / or toughness to the incision area of ​​the dental restoration while the wear of other teeth (e.g., the occlusal surface relative to the natural teeth) may not be too high.

[0269] The flexural strength of the bottom layer may be at least 900 MPa, at least 1000 MPa, at least 1050 MPa. The flexural strength of the bottom layer may be at most 1500 MPa, at most 1300 MPa, or at most 1200 MPa. The flexural strength of the bottom layer may be in the range of 900 MPa to 1500 MPa, 1000 MPa to 1300 MPa, or 1050 MPa to 1200 MPa. The fracture toughness K of the bottom layer may be at most 1500 MPa, at most 1300 MPa, or at most 1200 MPa. IC Can be at least 3.6 MPa*m 1 / 2 , at least 3.8 MPa*m 1 / 2 or at least 4.0 MPa*m 1 / 2 The fracture toughness K of the bottom layer IC Can be up to 5.5 MPa*m 1 / 2 , up to 4.8 MPa*m 1 / 2 , up to 4.6 MPa*m 1 / 2 or up to 4.4 MPa*m 1 / 2 The fracture toughness K of the bottom layer IC It can be adjusted from 3.6 to 5.5 MPa*m1 / 2 , 3.8 to 4.8 MPa*m 1 / 2 , or 4.0 to 4.6 MPa*m 1 / 2 , or 4.0 to 4.4 MPa*m 1 / 2 Such strength and / or toughness are highly desirable for providing dental restorations with sufficient mechanical stability for most of their applications, including those requiring relatively low wall thicknesses. Such applications may be, but are not limited to, abutment-supported crowns or bridges, and in particular bridges where the dimensions of the connectors between the different elements of the bridge allow for an aesthetically pleasing clinical result.

[0270] In one embodiment, the fracture toughness K of the bottom layer is IC At least 3.8 MPa*m 1 / 2 , at least 4.0, or between 3.8 and 4.8 MPa*m 1 / 2 , or 4.0 to 4.4 MPa*m 1 / 2 %, or in a range of 6.4 wt % to 7.2 wt % based on the total weight of the bottom layer.

[0271] The fracture toughness K of at least one intermediate layer IC Can be at least 2.6 MPa*m 1 / 2 or at least 2.8 MPa*m 1 / 2 The fracture toughness K of at least one intermediate layer IC Can be up to 4.4 MPa*m 1 / 2 or up to 4.2 MPa*m 1 / 2 The fracture toughness K of at least one intermediate layer IC Can be in the range of 2.6 to 4.4 MPa*m 1 / 2 or 2.8 to 4.2 MPa*m 1 / 2 within the range.

[0272] The fracture toughness K of the middle layer adjacent to the top layer IC May be at least 2.6 MPa*m measured using a load of 5 kg 1 / 2 , at least 2.8 MPa*m 1 / 2 or at least 2.9 MPa*m 1 / 2 The fracture toughness K of the middle layer adjacent to the top layer IC Can be up to 3.6 MPa*m measured with a load of 5 kg 1 / 2 , up to 3.4 MPa*m 1 / 2 or at most 3.3 MPa*m 1 / 2The fracture toughness K of the middle layer adjacent to the top layer IC It can be measured with a load of 5 kg and is between 2.6 and 3.6 MPa*m 1 / 2 , 2.8 to 3.4 MPa*m 1 / 2 or 2.9 to 3.3 MPa*m 1 / 2 within the range.

[0273] The fracture toughness K of the intermediate layer adjacent to the bottom layer IC May be at least 3.1 MPa*m measured using a load of 5 kg 1 / 2 , at least 3.3 MPa*m 1 / 2 or at least 3.4 MPa*m 1 / 2 The fracture toughness K of the intermediate layer adjacent to the bottom layer IC Can be up to 4.2 MPa*m measured with a load of 5 kg 1 / 2 , up to 4.0 MPa*m 1 / 2 or up to 3.8 MPa*m 1 / 2 The fracture toughness K of the intermediate layer adjacent to the bottom layer IC Can be measured with a load of 5 kg and be between 3.1 and 4.2 MPa*m 1 / 2 , 3.3 to 4.0 MPa*m 1 / 2 or 3.4 to 3.8 MPa*m 1 / 2 within the range.

[0274] The pre-sintered multi-layer dental mill blank may comprise the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, wherein when fully sintered by a rapid sintering method, a representative test cross section of the layers may have a fracture toughness K of IC :

[0275] 2.5 to 3.5 MPa*m measured with a load of 2.5 kg 1 / 2 , 2.7 to 3.3 MPa*m 1 / 2 or 2.8 to 3.2 MPa*m 1 / 2 The top layer L4 within the range,

[0276] 2.6 to 3.6 MPa*m measured with a 5 kg load 1 / 2 , 2.8 to 3.4 MPa*m 1 / 2 or 2.9 to 3.3 MPa*m 1 / 2 The range of the middle layer L3,

[0277] 3.1 to 4.2 MPa*m measured with a 5 kg load 1 / 2 , 3.3 to 4.0 MPa*m 1 / 2or 3.4 to 3.8 MPa*m 1 / 2 The range of the middle layer L2,

[0278] 3.6 to 4.8 MPa*m measured with a 10 kg load 1 / 2 , 3.8 to 4.6 MPa*m 1 / 2 or 3.9 to 4.4 MPa*m 1 / 2 within the range of the underlying L1.

[0279] When fully sintered by the rapid sintering method, the representative test cross-section may have a flexural strength that decreases from the bottom layer to the top layer, such that the bottom layer has a higher flexural strength than at least one intermediate layer, and at least one intermediate layer has a higher flexural strength than the top layer. When fully sintered by the rapid sintering method, the representative test cross-section may have a flexural strength that decreases layer by layer from the bottom layer to the top layer.

[0280] When fully sintered by the rapid sintering method, a representative test section may have a fracture toughness K decreasing from the bottom layer to the top layer. IC , so that the bottom layer has a higher fracture toughness K than at least one intermediate layer IC , and at least one intermediate layer has a higher fracture toughness K than the top layer IC When fully sintered by the rapid sintering method, a representative test section may have a fracture toughness K that decreases layer by layer from the bottom layer to the top layer. IC .

[0281] In addition to or instead of the properties of the fully sintered representative test sections as described herein, the pre-sintered multi-layer dental mill blank can be defined by its composition as described herein (eg, in the following sections).

[0282] 2. Composition

[0283] The pre-sintered multilayer dental mill blank according to the present invention may be defined by its components, the composition of its layers and / or the overall composition of the dental mill blank (ie the composition of its combined layers).

[0284] One embodiment of the present invention provides a pre-sintered multi-layer dental mill blank comprising a top layer, a bottom layer, and at least one middle layer, each layer comprising zirconium oxide and yttrium oxide, and the yttrium oxide content of each layer increases from the bottom layer to the top layer.

[0285] 2.1 Zirconium oxide (ZrO2) and yttrium oxide (Y2O3)

[0286] The pre-sintered multi-layer dental mill blank can be a pre-sintered multi-layer zirconia ceramic dental mill blank. Thus, the pre-sintered multi-layer dental mill blank can comprise zirconia as a major component. The pre-sintered multi-layer dental mill blank can comprise zirconia in an amount of at least 80 wt%, at least 85 wt%, at least 89 wt%, at most 95 wt%, at most 93 wt%, or at most 91 wt%, or in a range of 80 wt% to 95 wt%, 85 wt% to 93 wt%, or 89 wt% to 91 wt%, based on the total weight of the pre-sintered multi-layer dental mill blank.

[0287] Each layer may comprise zirconium oxide in an amount of at least 80%, at least 85%, at least 87%, or at least 88% by weight, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental mill blank. Each layer may comprise zirconium oxide in an amount of at most 95%, at most 94%, at most 93%, or at most 92% by weight, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental mill blank. Each layer may comprise zirconium oxide in an amount in the range of 80% to 95%, 85% to 94%, 87% to 93%, or 88% to 92% by weight, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental mill blank. For example, the top layer may comprise zirconium oxide in an amount in the range of 80% to 92%, such as in the range of 85% to 91%, or in the range of 87% to 90%, based on the total weight of the top layer. The base layer may comprise 85% to 94% by weight, such as in the range of 88% to 94% by weight, such as in the range of 90% to 92% by weight, of zirconium oxide, based on the total weight of the base layer. Each of the at least one intermediate layer may comprise 82% to 94% by weight, such as in the range of 85% to 93% by weight, such as in the range of 87% to 92% by weight, of zirconium oxide, based on the total weight of the respective layer of the at least one intermediate layer.

[0288] Zirconia is typically present in the form of yttria-stabilized zirconia. The pre-sintered multi-layer dental mill blank can comprise yttria-stabilized zirconia in an amount of at least 80%, at least 90%, at least 95%, at least 97%, or in a range of 80% to 99.5%, 90% to 99.5%, 95% to 99.0%, or 97% to 98.5%, based on the total weight of the pre-sintered multi-layer dental mill blank. The pre-sintered multi-layer dental mill blank can comprise zirconium oxide, yttria, and hafnium dioxide in an amount of at least 90%, at least 95%, at least 98%, at most 99.8%, at most 99.4%, at most 99.2%, or in a combined weight amount within a range of 90% to 99.8%, 95% to 99.5%, or 98% to 99.2%, based on the total weight of the pre-sintered multi-layer dental mill blank. Each layer may comprise a combined amount of zirconium oxide and yttrium oxide of at least 80 wt%, at least 90 wt%, at least 95 wt%, or at least 96 wt%, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental milling blank. Each layer may comprise a combined amount of zirconium oxide and yttrium oxide of at most 99.8 wt%, at most 99.5 wt%, at most 99.0 wt%, or at most 98.5 wt%, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental milling blank. Each layer may comprise a combined amount of zirconium oxide and yttrium oxide of 80 wt% to 99.8 wt%, 90 wt% to 99.5 wt%, 95 wt% to 99.0 wt%, or 96 wt% to 98.5 wt%, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental milling blank.

[0289] Each layer of the pre-sintered multi-layer dental mill blank typically comprises zirconium oxide and yttrium oxide. The yttrium oxide content of the layers increases from the bottom layer to the top layer. The yttrium oxide content of the layers may increase from the bottom layer to the top layer, such that the bottom layer has a lower yttrium oxide content than at least one intermediate layer, and the at least one intermediate layer has a lower yttrium oxide content than the top layer. Thus, one embodiment of the present invention provides a pre-sintered multi-layer dental mill blank comprising a top layer, a bottom layer, and at least one intermediate layer, each layer comprising zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, such that the bottom layer has a lower yttrium oxide content than at least one intermediate layer, and the at least one intermediate layer has a lower yttrium oxide content than the top layer. In one embodiment, the pre-sintered multi-layer dental mill blank comprises a plurality of intermediate layers, wherein not every intermediate layer has an increasing yttrium oxide content layer by layer in a direction from the bottom layer to the top layer.

[0290] However, it is preferred that the yttrium oxide content of each layer increases from the bottom layer to the top layer. The yttrium oxide content of the layers typically increases from the bottom layer to the top layer. Thus, yttrium oxide is typically present in different weight amounts in different layers of the pre-sintered mill blank. Without wishing to be bound by theory, it is believed that the increasing yttrium oxide content from layer to layer contributes to the natural appearance of the final dental restoration, with a gradual change in translucency from bottom to top.

[0291] The top layer can comprise at least 7.0 wt%, at least 8.0 wt%, at least 9.0 wt%, or at least 9.5 wt% yttrium oxide, based on the total weight of the top layer. The top layer can comprise at most 13.0 wt%, at most 12.0 wt%, at most 11.0 wt%, or at most 10.5 wt% yttrium oxide, based on the total weight of the top layer. The top layer can comprise yttrium oxide in an amount by weight ranging from 7.0 wt% to 13.0 wt%, from 8.0 wt% to 12.0 wt%, from 9.0 wt% to 11.0 wt%, or from 9.5 wt% to 10.5 wt%, based on the total weight of the top layer.

[0292] The bottom layer may comprise at least 4.0%, at least 5.0%, at least 5.5%, or at least 6.0% yttrium oxide by weight, based on the total weight of the bottom layer. The bottom layer may comprise at most 8.0%, at most 7.5%, at most 7.0%, or at most 6.8% yttrium oxide, based on the total weight of the bottom layer. The bottom layer may comprise from 4.0% to 8.0%, from 5.0% to 7.5%, from 5.5% to 7.0%, or from 6.0% to 6.8% yttrium oxide, based on the total weight of the bottom layer. In one embodiment, the top layer comprises yttrium oxide in an amount of at least 9.0%, such as at least 9.5%, such as in the range of 9.5% to 10.5%, based on the total weight of the top layer, and the bottom layer comprises yttrium oxide in an amount of at most 7.5%, such as at most 7.0%, such as in the range of 5.5% to 7.5%, based on the total weight of the bottom layer. In one embodiment, the top layer comprises yttrium oxide in an amount ranging from 9.0 wt% to 12.0 wt% based on the total weight of the top layer, and the bottom layer comprises yttrium oxide in an amount ranging from 5.5 wt% to 7.5 wt% based on the total weight of the bottom layer.

[0293] Each of the at least one intermediate layer may contain yttrium oxide in an amount of at least 5.0 wt%, at least 6.0 wt%, at least 6.5 wt%, or at least 7.0 wt%, based on the total weight of the corresponding layer of the at least one intermediate layer. Each of the at least one intermediate layer may contain yttrium oxide in an amount of at most 11.0 wt%, at most 10.5 wt%, at most 10.0 wt%, or 9.5 wt%, based on the total weight of the corresponding layer of the at least one intermediate layer. Each of the at least one intermediate layer may contain yttrium oxide in an amount ranging from 5.0 wt% to 11.0 wt%, from 6.0 wt% to 10.5 wt%, from 6.5 wt% to 10.0 wt%, or from 7.0 wt% to 9.5 wt%, based on the total weight of the corresponding layer of the at least one intermediate layer.

[0294] The pre-sintered multi-layer dental mill blank may comprise or may consist of the following layers:

[0295] Top floor L4,

[0296] Middle layer L3,

[0297] Middle layer L2,

[0298] Bottom layer L1,

[0299] the top layer L4 comprises yttrium oxide in an amount by weight ranging from 7.0 wt% to 13.0 wt%, from 8.0 wt% to 12.0 wt%, from 9.0 wt% to 11.0 wt%, or from 9.5 wt% to 10.5 wt%, based on the total weight of the top layer,

[0300] the intermediate layer L3 contains yttrium oxide in an amount by weight ranging from 6.0 wt % to 11.0 wt %, from 7.5 wt % to 10.5 wt %, from 8.5 wt % to 10.0 wt %, or from 9.0 wt % to 9.5 wt %, based on the total weight of the intermediate layer L3,

[0301] The intermediate layer L2 contains yttrium oxide in an amount by weight ranging from 4.5 wt% to 9.0 wt%, 5.5 wt% to 8.0 wt%, 6.0 wt% to 7.5 wt%, or 6.5 wt% to 7.3 wt%, based on the total weight of the intermediate layer L2, and

[0302] The underlayer L1 includes yttrium oxide in an amount by weight ranging from 4.0 wt% to 9.0 wt%, 5.0 wt% to 8.0 wt%, 5.5 wt% to 7.5 wt%, or 6.0 wt% to 6.8 wt%, based on the total weight of the underlayer.

[0303] The yttrium oxide content of a layer can be defined by the difference between the weight amounts of the two layers expressed as a percentage point value. For example, the top layer can have an yttrium oxide content (in weight %) that is at least 1.0 percentage point, at least 2.0 percentage points, at least 2.5 percentage points, or at least 3.0 percentage points higher, based on the total weight of the top layer, than the yttrium oxide content (in weight %) of the bottom layer, based on the total weight of the bottom layer. The top layer can have an yttrium oxide content (in weight %) that is at most 8.0 percentage points, at most 6.0 percentage points, at most 5.0 percentage points, or at most 4.0 percentage points higher, based on the total weight of the top layer, than the yttrium oxide content (in weight %) of the bottom layer, based on the total weight of the bottom layer. The top layer has an yttrium oxide content that is at most 1.0 percentage point to 8.0 percentage points, 2.0 percentage points to 6.0 percentage points, 2.5 percentage points to 5.0 percentage points, or 3.0 percentage points to 4.0 percentage points higher, based on the total weight of the top layer, than the yttrium oxide content of the bottom layer, based on the total weight of the bottom layer.

[0304] Each layer can have an yttrium oxide content (in weight %) that differs from the yttrium oxide content (in weight %) of an adjacent layer by at least 0.3 percentage points, at least 0.5 percentage points, at most 3.0 percentage points, at most 2.5 percentage points, or from 0.3 percentage points to 3.0 percentage points or from 0.5 percentage points to 2.5 percentage points, where the yttrium oxide content of the layer is based on the total weight of the layer.

[0305] The yttrium oxide present in the layers of the pre-sintered multi-layer dental mill blank, or the yttrium oxide present in the entire pre-sintered multi-layer dental mill blank, can be a combination of type I and type II yttrium oxide. Similarly, the yttrium oxide content of the layers of the pre-sintered multi-layer dental mill blank, or the yttrium oxide content of the entire pre-sintered multi-layer dental mill blank, can be a combination of type I and type II yttrium oxide. In one embodiment, the top layer comprises yttrium oxide as type I yttrium oxide, at least one intermediate layer comprises yttrium oxide as a combination of type I and type II yttrium oxide, and the bottom layer comprises yttrium oxide as a combination of type I and type II yttrium oxide.

[0306] Each of the layers of the pre-sintered multilayer dental mill blank is preferably obtainable from a yttria-stabilized zirconia powder or a mixture of different yttria-stabilized zirconia powders. Each of the layers of the pre-sintered multilayer dental mill blank is preferably obtainable from a different yttria-stabilized zirconia powder or a mixture of different yttria-stabilized zirconia powders. Preferred yttria-stabilized zirconia powders are 3 mol% yttria-stabilized zirconia powder (3Y-YSZ), 4 mol% yttria-stabilized zirconia powder (4Y-YSZ), and ≥5 mol% yttria-stabilized zirconia powder (5Y-YSZ). In one embodiment, each of the layers of the pre-sintered multi-layer dental mill blank can be obtained from a different yttria-stabilized zirconia powder or a mixture of different yttria-stabilized zirconia powders selected from the group consisting of 3 mol% yttria-stabilized zirconia powder (3Y-YSZ), 4 mol% yttria-stabilized zirconia powder (4Y-YSZ), ≥5 mol% yttria-stabilized zirconia powder (5Y-YSZ), and mixtures thereof. For example, these powders are commercially available from DAIICHI KIGENSOKAGAKU KOGYO CO., LTD. under the brand names HSY-3FSD-103, HSY-0250, and HSY-0451, respectively.

[0307] In one embodiment, the pre-sintered multi-layer dental mill blank comprises or consists of:

[0308] Top layer L4, which can be obtained from powder P3,

[0309] an intermediate layer L3, obtainable from a mixture of powders P2 and P3,

[0310] an intermediate layer L2, obtainable from a mixture of powders P1 and P2,

[0311] a bottom layer L1, obtainable from powder P1, and

[0312] Powders P1 to P3 are three yttria-stabilized zirconia powders, wherein powder P1 has a yttria content in the range of 4.5 wt % to 6.1 wt % (e.g., in the range of 4.9 wt % to 6.0 wt %), powder P2 has a yttria content in the range of 6.2 wt % to 7.9 wt % (e.g., in the range of 6.5 wt % to 7.6 wt %), and powder P3 has a yttria content in the range of 8.0 wt % to 11.0 wt % (e.g., in the range of 9.0 wt % to 10.5 wt %).

[0313] Layers L4 to L1 can be obtained by pre-sintering a top powder layer of powder P3, an intermediate powder layer of powders P2 and P3, an intermediate powder layer of powders P1 and P2, and a bottom powder layer of powder P1, wherein each of powders P1 to P3 can be optionally treated with one or more additives (e.g., coloring additives, sintering activator precursors, and / or sintering inhibitor precursors).

[0314] In one embodiment, the pre-sintered multi-layer dental mill blank comprises or consists of:

[0315] Top layer L4, which is a pre-sintered top powder layer of powder P3,

[0316] an intermediate layer L3, which is a pre-sintered intermediate powder layer of a mixture of powders P2 / P3,

[0317] an intermediate layer L2, which is a pre-sintered intermediate powder layer of a mixture of powders P1 / P2,

[0318] a bottom layer L1 which is a pre-sintered bottom powder layer of powder P1, and

[0319] Powders P1 to P3 are three yttria-stabilized zirconia powders, wherein powder P1 has a yttria content in the range of 4.5 wt % to 6.1 wt % (e.g., in the range of 4.9 wt % to 6.0 wt %), powder P2 has a yttria content in the range of 6.2 wt % to 7.9 wt % (e.g., in the range of 6.5 wt % to 7.6 wt %), and powder P3 has a yttria content in the range of 8.0 wt % to 11.0 wt % (e.g., in the range of 9.0 wt % to 10.5 wt %).

[0320] The yttrium oxide content (in weight %) of powders P1 and P2 and the yttrium oxide content (in weight %) of powders P2 and P3 can differ by at least 0.7 percentage points, at least 1.0 percentage points, at least 1.2 percentage points, at most 3.0 percentage points, at most 2.8 percentage points, at most 2.5 percentage points, such as from 0.7 percentage points to 3.0 percentage points, from 1.0 percentage points to 2.8 percentage points, or from 1.2 percentage points to 2.5 percentage points.

[0321] The mixture of powders P1 / P2 may contain powders P1 and P2 in a weight ratio of powder P1 to powder P2 in the range of 10:90 to 40:60, in the range of 15:85 to 35:65, in the range of 20:80 to 30:70, or in the range of 22:78 to 28:72. The mixture of powders P2 / P3 may contain powders P2 and P3 in a weight ratio of powder P2 to powder P3 in the range of 10:90 to 40:60, in the range of 15:85 to 35:65, in the range of 20:80 to 30:70, or in the range of 22:78 to 28:72. In one embodiment, the mixture of powders P1 / P2 contains powders P1 and P2 in a weight ratio of powder P1 to powder P2 in the range of 10:90 to 40:60, in the range of 15:85 to 35:65, in the range of 20:80 to 30:70 or in the range of 22:78 to 28:72, and the mixture of powders P2 / P3 contains powders P2 and P3 in a weight ratio of powder P2 to powder P3 in the range of 10:90 to 40:60, in the range of 15:85 to 35:65, in the range of 20:80 to 30:70 or in the range of 22:78 to 28:72.

[0322] 2.2 Hafnium dioxide (HfO2)

[0323] The pre-sintered multi-layer dental mill blank can include hafnium dioxide. The hafnium dioxide can be part of or can be derived from a ceramic-based component (e.g., yttria-stabilized zirconia powder) used to prepare at least a portion of the powder layer of the green body of the pre-sintered multi-layer dental mill blank. For example, the hafnium dioxide can be part of the yttria-stabilized zirconia powder.

[0324] The pre-sintered multi-layer dental mill blank may comprise hafnium dioxide in an amount by weight of at least 0.5 wt%, at least 1.0 wt%, at least 1.2 wt%, at most 5.0 wt%, at most 3.0 wt%, or at most 2.0 wt%, or in a range of 0.5 wt% to 5.0 wt%, 1.0 wt% to 3.0 wt%, or 1.2 wt% to 2.0 wt%, based on the total weight of the pre-sintered multi-layer dental mill blank.

[0325] Each layer of the pre-sintered multi-layer dental mill blank can contain hafnium dioxide. The hafnium dioxide can be present in a specific weight ratio to zirconium oxide. Each layer can contain hafnium dioxide in a weight ratio to zirconium oxide in the range of 0:100 to 5:95, 1:99 to 4:96, 2:98 to 3:97, or 2:98, based on the total weight of hafnium dioxide and zirconium oxide of the respective layer of the pre-sintered multi-layer dental mill blank. Each layer can contain hafnium dioxide in an amount of at least 0.1 wt%, at least 0.5 wt%, at least 1.5 wt%, at most 5.0 wt%, at most 3.0 wt%, or at most 2.0 wt%, such as in the range of 0.1 wt% to 5.0 wt%, such as in the range of 0.5 wt% to 3.0 wt%, such as in the range of 1.5 wt% to 2.0 wt%, based on the total weight of the respective layer.

[0326] Each layer can be defined by the combined amounts of zirconium oxide, yttrium oxide, and hafnium dioxide. Each layer can comprise a combined amount of zirconium oxide, yttrium oxide, and hafnium dioxide of at least 80 weight percent, at least 90 weight percent, at least 95 weight percent, or at least 98 weight percent, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental abrasive blank. Each layer can comprise a combined amount of zirconium oxide, yttrium oxide, and hafnium dioxide of at most 99.8 weight percent, at most 99.6 weight percent, at most 99.4 weight percent, or at most 99.2 weight percent, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental abrasive blank. Each layer can comprise a combined amount of zirconium oxide, yttrium oxide, and hafnium dioxide of 80 weight percent to 99.8 weight percent, 90 weight percent to 99.6 weight percent, 95 weight percent to 99.4 weight percent, or 98 weight percent to 99.2 weight percent, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental abrasive blank.

[0327] 2.3 Alumina (Al2O3)

[0328] The pre-sintered multi-layer dental mill blank may comprise alumina. The alumina may be part of or may be derived from a ceramic-based component (e.g., yttria-stabilized zirconia powder) used to prepare at least a portion of the powder layers of the green body of the pre-sintered multi-layer dental mill blank.

[0329] The pre-sintered multi-layer dental mill blank may comprise aluminum oxide in an amount by weight of at least 0.005 wt%, at least 0.02 wt%, or at least 0.05 wt%, at most 0.4 wt%, at most 0.2 wt%, or at most 0.1 wt%, or in a range of 0.005 wt% to 0.4 wt% (e.g., 0.005 wt% to 0.1 wt%), 0.02 wt% to 0.2 wt%, or 0.05 wt% to 0.1 wt%, based on the total weight of the pre-sintered multi-layer dental mill blank.

[0330] The layers of the pre-sintered multilayer dental mill blank may have different weight contents of aluminum oxide. The top layer may comprise aluminum oxide in an amount of less than 0.05 wt %, or less than 0.02 wt %, or less than 0.01 wt %, based on the total weight of the top layer. It has been found that when the top layer comprises a particularly low amount of aluminum oxide, the top layer or a portion thereof (e.g., a region of a dental restoration obtained at least partially from the top layer) that is fully sintered by a rapid sintering process has advantageous optical properties. Without wishing to be bound by theory, it is believed that this may be due to a reduction in the number of pores (i.e., intra-particle pores and inter-particle pores) present in the fully sintered top layer or a portion thereof. It is believed that the pores diffract or scatter light in an undesirable manner in the fully sintered dental restoration and may therefore be detrimental to the optical properties of the fully sintered dental restoration (e.g., its translucency).

[0331] In one embodiment, the pre-sintered multi-layer dental mill blank comprises

[0332] Top floor,

[0333] bottom layer, and

[0334] At least one intermediate layer,

[0335] Each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, and

[0336] The top layer comprises aluminum oxide in an amount less than 0.01 wt %, based on the total weight of the top layer.

[0337] The yttrium oxide content may increase from the bottom layer to the top layer such that the bottom layer has a lower yttrium oxide content than at least one intermediate layer and at least one intermediate layer has a lower yttrium oxide content than the top layer. Preferably, the yttrium oxide content of the layers increases layer by layer from the bottom layer to the top layer.

[0338] In one embodiment, the pre-sintered multi-layer dental mill blank comprises

[0339] Top floor,

[0340] bottom layer, and

[0341] At least one intermediate layer,

[0342] Each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, preferably from layer to layer, and

[0343] The top layer comprises aluminum oxide in an amount less than 0.01 wt %, based on the total weight of the top layer.

[0344] The top layer may have a lower aluminum oxide weight content than the bottom layer. The top layer may have the lowest aluminum content of all the layers. The aluminum content of the layers may increase from the top layer in the direction of the bottom layer by at least 2 layers.

[0345] The bottom layer may have a higher alumina weight content than the alumina weight content of the top layer and the alumina weight content of an intermediate layer adjacent to the top layer.

[0346] The pre-sintered multi-layer dental mill blank may comprise or may consist of the following layers:

[0347] Top floor L4,

[0348] Middle layer L3,

[0349] Middle layer L2,

[0350] Bottom layer L1,

[0351] The aluminum oxide weight content in each of layer L1 and layer L2 is higher than the aluminum oxide weight content in layer L3 , and the aluminum oxide weight content in layer L3 is higher than the aluminum oxide weight content in layer L4 .

[0352] The top layer may comprise alumina in an amount less than 0.01 wt %, based on the total weight of the top layer.The top layer may be substantially free of alumina.

[0353] The bottom layer may comprise at least 0.01 wt%, at least 0.02 wt%, or at least 0.05 wt% aluminum oxide, based on the total weight of the bottom layer. The bottom layer may comprise at most 0.50 wt%, at most 0.40 wt%, at most 0.20 wt%, or at most 0.15 wt% aluminum oxide, based on the total weight of the bottom layer. The bottom layer may comprise from 0.01 wt% to 0.50 wt%, from 0.02 wt% to 0.40 wt%, from 0.05 wt% to 0.20 wt%, or from 0.05 wt% to 0.15 wt% aluminum oxide, based on the total weight of the bottom layer.

[0354] Each of the at least one intermediate layer may contain at least 0.01 wt%, at least 0.02 wt%, or at least 0.05 wt% aluminum oxide, based on the total weight of the corresponding layer of the at least one intermediate layer. Each of the at least one intermediate layer may contain at most 0.5 wt%, at most 0.20 wt%, or at most 0.15 wt% aluminum oxide, based on the total weight of the corresponding layer of the at least one intermediate layer. Each of the at least one intermediate layer may contain from 0.01 wt% to 0.5 wt%, from 0.02 wt% to 0.20 wt%, or from 0.02 wt% to 0.15 wt% aluminum oxide, based on the total weight of the corresponding layer of the at least one intermediate layer.

[0355] The intermediate layer adjacent to the bottom layer may contain at least 0.01 wt%, at least 0.02 wt%, or at least 0.05 wt% aluminum oxide, based on the total weight of the intermediate layer. The intermediate layer adjacent to the bottom layer may contain at most 0.5 wt%, at most 0.20 wt%, or at most 0.15 wt% aluminum oxide, based on the total weight of the intermediate layer. The intermediate layer adjacent to the bottom layer may contain from 0.01 wt% to 0.5 wt%, from 0.02 wt% to 0.20 wt%, or from 0.05 wt% to 0.15 wt% aluminum oxide, based on the total weight of the intermediate layer.

[0356] The intermediate layer adjacent to the top layer may comprise at least 0.01 wt %, at least 0.02 wt % aluminum oxide, based on the total weight of the intermediate layer. The intermediate layer adjacent to the top layer may comprise at most 0.20 wt %, or at most 0.10 wt % aluminum oxide, based on the total weight of the intermediate layer. The intermediate layer adjacent to the top layer may comprise from 0.01 wt % to 0.20 wt %, or from 0.02 wt % to 0.10 wt % aluminum oxide, based on the total weight of the intermediate layer.

[0357] 2.4 Sintering activator

[0358] The pre-sintered multilayer dental mill blank may contain a sintering activator. The sintering activator may be obtained from a sintering activator precursor. The sintering activator may be obtained by converting a sintering activator precursor into a sintering activator when pre-sintering the green body of the multilayer dental mill blank. The sintering activator precursor may be present in the powder layer of the green body. For example, the sintering activator precursor may be present on the surface of the powder particles of the powder layer. Prior to the pre-sintering step, the sintering activator precursor may be added as a surface treatment agent to the yttria-stabilized zirconia powder or the mixture of yttria-stabilized zirconia powders (e.g., by treating the surface of the particles of the powder or powder mixture).

[0359] The pre-sintered multi-layer dental mill blank may comprise a sintering activator in an amount by weight of at least 0.02 wt%, at least 0.05 wt%, at least 0.10 wt%, at least 0.15 wt%, at most 0.8 wt%, at most 0.45 wt%, at most 0.30 wt%, or at most 0.25 wt%, or in a range of 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.45 wt%, 0.10 wt% to 0.30 wt%, or 0.15 wt% to 0.25 wt%, based on the total weight of the pre-sintered multi-layer dental mill blank.

[0360] The top layer of the pre-sintered multi-layer dental mill blank may comprise a sintering activator. In one embodiment, the pre-sintered multi-layer dental mill blank comprises

[0361] Top floor,

[0362] bottom layer, and

[0363] At least one intermediate layer,

[0364] Each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, and

[0365] The top layer contains a sintering activator.

[0366] The yttrium oxide content may increase from the bottom layer to the top layer such that the bottom layer has a lower yttrium oxide content than at least one intermediate layer and at least one intermediate layer has a lower yttrium oxide content than the top layer. Preferably, the yttrium oxide content of the layers increases layer by layer from the bottom layer to the top layer.

[0367] In one embodiment, the pre-sintered multi-layer dental mill blank comprises

[0368] Top floor,

[0369] bottom layer, and

[0370] At least one intermediate layer,

[0371] Each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, preferably from layer to layer, and

[0372] The top layer contains a sintering activator.

[0373] When the yttria content of the layers increases from the bottom layer to the top layer, the top layer has the highest yttria content of all the layers. Generally, the time and / or temperature required to sinter a material comprising zirconium oxide and yttria to full density increases with increasing yttria content. Therefore, when a sintering activator is included in the top layer, densification of the top layer or a portion prepared therefrom (e.g., at least a portion of the cutout area of ​​a dental restoration precursor) can be achieved at a lower maximum sintering temperature and / or a shorter sintering time. The sintering curve of the top layer or a portion prepared therefrom may be shifted to a lower temperature. When a sintering activator is present, the top layer of a portion prepared therefrom can be completely sintered in a short time while still achieving very good optical properties.

[0374] Each layer of a pre-sintered multilayer dental mill blank may also contain a sintering activator. When a sintering activator is included in each layer, densification of the layer or a portion thereof (e.g., a dental restoration precursor) can be achieved at a lower maximum sintering temperature and / or a shorter sintering time. The sintering curve of each layer or portion thereof may be shifted toward a lower temperature. When a sintering activator is present in each layer, the layer or portion thereof can be completely sintered in a shorter time while still achieving good optical properties.

[0375] It was further discovered that a sintering activator (e.g., zinc oxide or gallium oxide) can be combined with a sintering inhibitor (e.g., type II yttrium oxide) (e.g., in a bottom layer) while still achieving a shift of the sintering curve to lower temperatures and good optical properties of the product despite the presence of the sintering inhibitor. Without wishing to be bound by theory, it is believed that the sintering activator can be compatible with the sintering inhibitor because the sintering activator may have a more significant effect on the higher temperature range of the sintering curve (e.g., temperatures above 1100° C.), while the sintering inhibitor may have a more significant effect on the lower temperature range of the sintering curve (e.g., 900° C. to 1100° C.).

[0376] The sintering activator is a metal oxide. The sintering activator can be zinc oxide (ZnO), gallium oxide (Ga2O3) or a combination thereof. It has been found that in the context of the present invention, zinc oxide or gallium oxide, and in particular zinc oxide, can be particularly used as a sintering activator. In one embodiment, the sintering activator is zinc oxide, gallium oxide or a combination thereof. In a preferred embodiment, the sintering activator is zinc oxide. In one embodiment, the top layer comprises a sintering activator, which is zinc oxide, gallium oxide or a combination thereof. In a preferred embodiment, the top layer comprises a sintering activator, which is zinc oxide. In one embodiment, the top layer comprises a sintering activator that is not aluminum oxide.

[0377] Each of the layers of the pre-sintered multilayer dental mill blank can comprise a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof). In one embodiment, each of the layers comprises a sintering activator that is zinc oxide, gallium oxide, or a combination thereof (e.g., zinc oxide).

[0378] The top layer may contain a higher weight amount of sintering activator than the bottom layer. For example, the weight amount [wt%] of the sintering activator in the top layer and the weight amount [wt%] of the sintering activator in the bottom layer may satisfy the following formula (A) or (B):

[0379] w(SA-BL) / w(SA-TL) ≤ 0.85 (A);

[0380] w(SA -BL) / w(SA -TL) ≤ 0.80 (B);

[0381] wherein w(SA-BL) is the weight amount of the sintering activator in the bottom layer based on the total weight of the bottom layer, and w(SA-TL) is the weight amount of the sintering activator in the top layer based on the total weight of the top layer.

[0382] In one embodiment, the weight amount of the sintering activator decreases from the top layer to the bottom layer.

[0383] The weight amount of sintering activator in each layer can be adjusted so that at least a portion of the sintering curves are aligned with each other, as is the portion of the sintering curve associated with the maximum sintering rate. The maximum sintering rate can be determined based on the sintering curve of the rapid sintering method. The sintering curve can be obtained by plotting the relative densification of the material as a function of the sintering temperature. As used herein, the maximum sintering rate is the point on the sintering curve at which the tangent to the curve has the highest negative slope. The maximum sintering rate can be achieved at the temperature T of the rapid sintering method.

[0384] In one embodiment, the pre-sintered multi-layer dental abrasive blank is characterized by providing a representative test section for each layer, and adjusting the weight amount of the sintering activator in each of the layers of the pre-sintered multi-layer dental abrasive blank so that when fully sintered by a rapid sintering method, each of the representative test sections has a maximum sintering rate at a temperature T, wherein the temperatures T of the representative test sections differ by no more than 40°C or by no more than 25°C.

[0385] The layers of the pre-sintered dental mill blank can include a specific amount of a sintering activator. The top layer can include a sintering activator in an amount of at least 0.02 wt%, at least 0.05 wt%, at least 0.10 wt%, or at least 0.15 wt%, based on the total weight of the top layer. The top layer can include a sintering activator in an amount of at most 0.8 wt%, at most 0.50 wt%, at most 0.30 wt%, or at most 0.20 wt%, based on the total weight of the top layer. The top layer can include a sintering activator in an amount ranging from 0.02 wt% to 0.8 wt%, from 0.05 wt% to 0.50 wt%, from 0.10 wt% to 0.30 wt%, or from 0.15 wt% to 0.20 wt%, based on the total weight of the top layer.

[0386] The bottom layer may contain a sintering activator in an amount of at least 0.02 wt%, at least 0.05 wt%, or at least 0.10 wt%, based on the total weight of the bottom layer. The bottom layer may contain a sintering activator in an amount of at most 0.80 wt%, at most 0.50 wt%, at most 0.30 wt%, or at most 0.17 wt%, based on the total weight of the bottom layer. The bottom layer may contain a sintering activator in an amount ranging from 0.02 wt% to 0.80 wt%, from 0.02 wt% to 0.50 wt%, from 0.05 wt% to 0.30 wt%, or from 0.10 wt% to 0.17 wt%, based on the total weight of the bottom layer.

[0387] Each layer may contain a sintering activator in an amount of at least 0.02 wt%, at least 0.05 wt%, or at least 0.10 wt%, based on the total weight of the corresponding layer. Each layer may contain a sintering activator in an amount of at most 0.8 wt%, at most 0.50 wt%, or at most 0.30 wt%, based on the total weight of the corresponding layer. Each layer may contain a sintering activator in an amount ranging from 0.02 wt% to 0.8 wt%, from 0.05 wt% to 0.50 wt%, or from 0.10 wt% to 0.30 wt%, based on the total weight of the corresponding layer.

[0388] The top layer may contain an amount of sintering activator by weight [%] greater than the amount by weight [%] of sintering activator present in the bottom layer based on the total weight of the bottom layer by at least 0.010 percentage points, at least 0.020 percentage points, or at least 0.030 percentage points, based on the total weight of the top layer. The top layer may contain an amount of sintering activator by weight [%] greater than the amount by weight [%] of sintering activator present in the bottom layer based on the total weight of the bottom layer by at most 0.50 percentage points, at most 0.20 percentage points, or at most 0.10 percentage points, based on the total weight of the top layer. The top layer may contain an amount of sintering activator by weight [%] greater than the amount by weight [%] of sintering activator present in the bottom layer based on the total weight of the bottom layer by at most 0.010 percentage points to 0.5 percentage points, 0.020 percentage points to 0.20 percentage points, or 0.030 percentage points to 0.10 percentage points, based on the total weight of the top layer.

[0389] It should be understood that when a pre-sintered multi-layer dental mill blank according to embodiments of the present invention, or any of its layers, is described herein as comprising a particular type of sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof), this does not exclude the possible presence of other additional sintering activators (unless explicitly stated).

[0390] 2.5 Sintering inhibitors

[0391] The pre-sintered multi-layer dental mill blank may contain a sintering inhibitor. The sintering inhibitor may be obtained from a sintering inhibitor precursor. The sintering inhibitor may be obtained by converting the sintering inhibitor precursor into a sintering inhibitor during the pre-sintering of the green body of the multi-layer dental mill blank. The sintering inhibitor precursor may be present in the powder layer of the green body. For example, the sintering inhibitor precursor may be present on the surface of the powder particles of the powder layer. Prior to the pre-sintering step, the sintering inhibitor precursor may be added as a surface treatment agent to the yttria-stabilized zirconia powder or the mixture of yttria-stabilized zirconia powders (e.g., by treating the surface of the grains of the powder or powder mixture).

[0392] The pre-sintered multi-layer dental mill blank may comprise a sintering inhibitor in an amount by weight of at least 0.1 wt%, at least 0.2 wt%, at least 0.3 wt%, at least 0.5 wt%, at most 2.5 wt%, at most 2.0 wt%, at most 1.5 wt%, or at most 1.2 wt%, or in a range of 0.1 wt% to 2.5 wt%, 0.2 wt% to 2.0 wt%, 0.3 wt% to 1.5 wt%, or 0.5 wt% to 1.2 wt%, based on the total weight of the pre-sintered multi-layer dental mill blank.

[0393] A sintering inhibitor can be present in one or more specific layers of a pre-sintered dental mill blank. The sintering inhibitor can affect the sintering curve of the layer or a part made therefrom, primarily in the lower temperature range (e.g., in the range of 900° C. to 1100° C.), but also in the range of maximum shrinkage. When a sintering inhibitor is present, the sintering curve of the ceramic material of the layer in the lower temperature range can be adjusted so that the sintering curve is more aligned with the sintering curve of the ceramic material of one or more other layers in the temperature range.

[0394] In one embodiment, the bottom layer comprises a sintering inhibitor. In one embodiment, the bottom layer comprises a sintering inhibitor, and each of the at least one intermediate layer comprises a sintering inhibitor. It is possible that each of the layers comprises a sintering inhibitor. In one embodiment, the weight content of the sintering inhibitor decreases from the bottom layer to the top layer.

[0395] The bottom layer may contain a sintering inhibitor in an amount of at least 0.4 wt%, at least 0.6 wt%, at least 0.8 wt%, up to 2.5 wt%, up to 2.0 wt%, up to 1.5 wt%, or in a range of 0.4 wt% to 2.5 wt%, 0.6 wt% to 2.0 wt%, or 0.8 wt% to 1.5 wt%, based on the total weight of the bottom layer.

[0396] Each of the at least one intermediate layer may contain a sintering inhibitor in an amount of at least 0.02 wt%, at least 0.05 wt%, at most 2.0 wt%, at most 1.5 wt%, at most 1.2, or in a range of 0.02 wt% to 2.0 wt%, 0.05 wt% to 1.5 wt%, or 0.05 wt% to 1.2 wt%, based on the total weight of the corresponding layer of the at least one intermediate layer.

[0397] The top layer may contain a sintering inhibitor in an amount by weight of at least 0.01 wt%, at least 0.02 wt%, at least 0.05 wt%, at most 1.0 wt%, at most 0.8 wt%, at most 0.5 wt%, in a range of 0.01 wt% to 1.0 wt%, 0.02 wt% to 0.8 wt%, or 0.05 wt% to 0.5 wt%, based on the total weight of the top layer.

[0398] The sintering inhibitor is a metal oxide. The sintering inhibitor can be, but is not necessarily limited to, La2O3, Yb2O3, Tm2O3, type II yttrium oxide, erbium oxide (Er2O3), or any combination thereof. In one embodiment, the sintering inhibitor is La2O3, type II yttrium oxide, erbium oxide (Er2O3), or any combination thereof. Optionally, the sintering inhibitor is type II yttrium oxide, erbium oxide, or a combination thereof. Preferably, the sintering inhibitor is type II yttrium oxide, optionally in combination with erbium oxide. In a preferred embodiment, the sintering inhibitor is a combination of type II yttrium oxide and erbium oxide.

[0399] Erbium oxide is also a coloring metal oxide. The weight amount of erbium oxide in a pre-sintered multilayer dental mill blank or any of its layers may vary depending on the pre-coloring of the dental mill blank. A layer of a lighter pre-colored dental mill blank may have a lower erbium oxide content than a layer of a darker pre-colored dental mill blank. When the sintering inhibitor is a combination of type II yttrium oxide and erbium oxide, the weight amount of type II yttrium oxide in a layer (e.g., the bottom layer and / or each of at least one intermediate layer) can be adjusted to the weight amount of erbium oxide. As a result, the sintering behavior of the layer, and in particular the bottom layer, can be advantageously aligned with the sintering behavior of one or more other layers of the mill blank.

[0400] In one embodiment, the underlayer comprises a sintering inhibitor that is a combination of type II yttrium oxide and erbium oxide based on the total weight of the underlayer, and wherein the amount of type II yttrium oxide in the underlayer is defined by the formula:

[0401]

[0402] in

[0403] A II-Y-BL is the molar amount of type II yttrium oxide in the bottom layer, A BL is the molar amount of type II yttrium oxide in the bottom layer that achieves the desired adjustment of the sintering curve in the absence of erbium oxide (ie, for a milled blank that is not pre-colored), A E-BL is the molar amount of erbium dioxide in the bottom layer, and A E-TL is the molar amount of erbium dioxide in the top layer.

[0404] A BL The molar amount may be equivalent to the weight of type II yttrium oxide in the range of 0.4 wt % to 1.5 wt %, 0.6 wt % to 1.2 wt %, or 0.8 wt % to 1.1 wt % based on the total weight of the bottom layer. E-BL and A E-TLTo achieve tooth shade, for example, match the tooth shade of the VITA Classic A1-D4® shade guide with the VITA Bleach shade manufactured by Vita Zahnfabrik or a similar tooth shade guide system. Additionally or alternatively, A E-BL and A E-TL , such that when fully sintered by the flash sintering method, representative test sections of the bottom and top layers have CIE L*a*b* values ​​as described herein.

[0405] The underlayer may comprise a sintering inhibitor which is type II yttrium oxide, optionally in combination with erbium oxide, and the underlayer may comprise type II yttrium oxide in an amount of at least 0.4 wt%, at least 0.6 wt%, at least 0.8 wt%, at most 1.5 wt%, at most 1.2 wt%, at most 1.1 wt%, or in a range of 0.4 wt% to 1.5 wt%, 0.6 wt% to 1.2 wt%, or 0.8 wt% to 1.1 wt%, based on the total weight of the underlayer.

[0406] Each of the at least one intermediate layer may comprise a sintering inhibitor which is type II yttrium oxide, optionally in combination with erbium oxide, and each of the at least two intermediate layers may comprise type II yttrium oxide in an amount of at least 0.02 wt%, at least 0.05 wt%, at most 1.0 wt%, at most 0.6 wt%, or in a range of 0.02 wt% to 1.0 wt%, 0.05 wt% to 1.0 wt%, or 0.05 wt% to 0.6 wt%, based on the total weight of the respective layer of the at least one intermediate layer.

[0407] The top layer may include a sintering inhibitor that is type II yttrium oxide and / or erbium oxide, and the top layer may include type II yttrium oxide in an amount ranging from 0.00 wt% to 0.03 wt%, 0.00 wt% to 0.02 wt%, or 0.00 wt% to 0.01 wt%, based on the total weight of the top layer. The top layer may be substantially free of type II yttrium oxide.

[0408] The pre-sintered multi-layer dental mill blank may comprise or may consist of the following layers:

[0409] Top floor L4,

[0410] Middle layer L3,

[0411] Middle layer L2,

[0412] Bottom layer L1,

[0413] wherein each of layers L3 to L1 comprises a sintering inhibitor which is type II yttrium oxide, optionally in combination with erbium oxide,

[0414] the intermediate layer L3 contains type II yttrium oxide in an amount by weight ranging from 0.02 wt % to 0.6 wt %, from 0.05 wt % to 0.4 wt %, or from 0.06 wt % to 0.2 wt %, based on the total weight of the intermediate layer L3,

[0415] The intermediate layer L2 contains type II yttrium oxide in an amount by weight ranging from 0.1 wt% to 1.0 wt%, from 0.2 wt% to 0.8 wt%, or from 0.4 wt% to 0.6 wt%, based on the total weight of the intermediate layer L2, and

[0416] the bottom layer L1 contains type II yttrium oxide in an amount by weight ranging from 0.4 wt% to 1.5 wt%, from 0.6 wt% to 1.2 wt%, or from 0.8 wt% to 1.1 wt%, based on the total weight of the bottom layer,

[0417] And optionally, the top layer L4 comprises type II oxide in an amount by weight ranging from 0.00 wt% to 0.03 wt%, 0.00 wt% to 0.02 wt%, or 0.00 wt% to 0.01 wt%, based on the total weight of the top layer, or is substantially free of type II oxide.

[0418] For example, by comparing the fracture toughness (e.g., fracture toughness K) of representative test sections of those layers fully sintered by the rapid sintering method as described herein. IC ), a layer of a pre-sintered multi-layer dental mill blank comprising a specific amount of yttrium oxide type I and yttrium oxide type II can be distinguished from a similar layer comprising the same specific amount of yttrium oxide only in the form of yttrium oxide type I. For example, a bottom layer of a pre-sintered multi-layer dental mill blank may comprise 5.6% by weight of yttrium oxide type I and 0.9% by weight of yttrium oxide type II. A representative test cross-section of the bottom layer, when fully sintered by a rapid sintering process, may have a fracture toughness K IC -A. A similar bottom layer of a similar pre-sintered multi-layer dental mill blank may contain 6.5 wt% type I yttrium oxide and no type II yttrium oxide. When fully sintered by the same rapid sintering method, a representative test section of the similar bottom layer may have a fracture toughness K IC -B. The bottom layer can be distinguished from similar bottom layers because the fracture toughness K IC -A is higher than the fracture toughness K IC -B.

[0419] It should be understood that when a pre-sintered multi-layer dental mill blank according to an embodiment of the present invention, or any of its layers, is described herein as comprising a specific sintering inhibitor (e.g., type II yttrium oxide, erbium oxide, or a combination thereof), this does not exclude the possible presence of other additional sintering inhibitors.

[0420] 2.6 Colorants

[0421] Pre-sintered multi-layer dental mill blanks are typically pre-colored. In one embodiment, the pre-sintered multi-layer dental mill blank is a pre-colored, pre-sintered multi-layer dental mill blank. The dental mill blank or its layers can be pre-colored to have a color that matches the VITA Classic A1-D4® color guide and the VITA bleached shades manufactured by Vita Zahnfabrik, or a similar tooth shade guide system (or to provide a color for at least a portion of a dental restoration prepared from the dental mill blank). The tooth shade can be, but is not limited to, A1, A2, A3.5, A4, B1, B2, B3, B4, C1, C2, C3, C4, D1, D2, D3, D4, BL1, or BL2. The tooth shade can also be a tooth shade, such as a light tooth shade, that is not part of the VITA Classic A1-D4® color guide and the VITA bleached shades manufactured by Vita Zahnfabrik, or a similar tooth shade guide system. The tooth shade can be an experimental light shade.

[0422] The pre-sintered multi-layer dental mill blank may contain a colored metal oxide. Suitable colored metal oxides may include, but are not limited to, oxides of Fe, Mn, Cr, Pr, Tb, Er, Yb, Ce, Co, Ni, Nd, Cu, Bi, and any mixtures thereof. The colored metal oxide may be present in an amount of at least 0.01 wt%, at least 0.02 wt%, at least 0.05 wt%, at most 1.5 wt%, at most 1.0 wt%, at most 0.8 wt%, or in a range of 0.01 wt% to 1.5 wt%, 0.02 wt% to 1.0 wt%, or 0.05 wt% to 0.8 wt%, based on the total weight of the pre-sintered multi-layer dental mill blank.

[0423] The colored metal oxide may comprise iron oxide. The pre-sintered multilayer dental mill blank may comprise iron oxide in an amount of at least 0.001 wt%, at least 0.005 wt%, at least 0.02 wt%, at most 0.4 wt%, at most 0.2 wt%, or at most 0.1 wt%, or in a range of 0.001 wt% to 0.4 wt%, 0.005 wt% to 0.2 wt%, or 0.02 wt% to 0.1 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0424] The colored metal oxide may comprise erbium oxide. The pre-sintered multilayer dental mill blank may comprise erbium oxide in an amount by weight of at least 0.01 wt%, at least 0.02 wt%, at least 0.05 wt%, at most 1.2 wt%, at most 1.0 wt%, or at most 0.7 wt%, or in a range of 0.01 wt% to 1.2 wt%, 0.05 wt% to 1.0 wt%, or 0.05 wt% to 0.7 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0425] Each layer of the pre-sintered multilayer dental mill blank can contain a colored metal oxide, including erbium oxide, and optionally iron oxide. Each layer can contain a colored metal oxide in an amount of at least 0.01 wt%, 0.02 wt%, at least 0.05 wt%, at most 1.5 wt%, at most 1.2 wt%, at most 1.0 wt%, or in a range of 0.01 wt% to 1.5 wt%, in a range of 0.02 wt% to 1.2 wt%, or in a range of 0.05 wt% to 1.0 wt%, based on the total weight of the corresponding layer.

[0426] 2.7 Composition of the composite layer

[0427] As described herein, the pre-sintered multi-layer dental mill blank can include different components in different weight amounts. It should be understood that the different components described herein (including their weight amounts) are also disclosed herein in combination.

[0428] In one embodiment, the pre-sintered multi-layer dental mill blank comprises (optionally consists essentially of or consists of):

[0429] 80% to 95% by weight, such as in the range of 85% to 93% by weight, such as in the range of 89% to 91% by weight, zirconium oxide,

[0430] ≤5 wt%, such as ≤3 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0431] 5.0% to 10.0% by weight, such as in the range of 6.0% to 9.0% by weight, such as in the range of 6.5% to 8.5% by weight of yttrium oxide,

[0432] ≤ 0.4 wt %, such as in the range of 0.02 wt % to 0.2 wt %, such as in the range of 0.05 wt % to 0.1 wt % aluminum oxide,

[0433] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.0 wt%, such as in the range of 0.05 to 0.8 wt% of colored metal oxide,

[0434] 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.45 wt%, 0.10 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0435] Each is based on the total weight of the pre-sintered multilayer dental mill blank, and the weight amounts of the components therein are optionally selected to total 100 wt%.

[0436] In one embodiment, the pre-sintered multi-layer dental mill blank comprises (optionally consists essentially of or consists of):

[0437] 80% to 95% by weight, such as in the range of 85% to 93% by weight, such as in the range of 89% to 91% by weight, zirconium oxide,

[0438] ≤5 wt%, such as ≤3 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0439] 5.0% to 10.0% by weight, such as in the range of 6.0% to 9.0% by weight, such as in the range of 6.5% to 8.5% by weight of yttrium oxide,

[0440] ≤ 0.4 wt %, such as in the range of 0.02 wt % to 0.2 wt %, such as in the range of 0.05 wt % to 0.1 wt % aluminum oxide,

[0441] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.0 wt%, such as in the range of 0.05 to 0.8 wt% of colored metal oxide,

[0442] 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.45 wt%, 0.10 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0443] 0.1 wt% to 2.0 wt%, such as in the range of 0.2 wt% to 1.5 wt%, such as in the range of 0.4 wt% to 1.2 wt% of a sintering inhibitor,

[0444] Each is based on the total weight of the pre-sintered multilayer dental mill blank, and the weight amounts of the components therein are optionally selected to total 100 wt%.

[0445] In one embodiment, the pre-sintered multi-layer dental mill blank comprises (optionally consists essentially of or consists of):

[0446] 80% to 95% by weight, such as in the range of 85% to 93% by weight, such as in the range of 89% to 91% by weight, zirconium oxide,

[0447] ≤5 wt%, such as ≤3 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0448] 5.0% to 10.0% by weight, such as in the range of 6.0% to 9.0% by weight, such as in the range of 6.5% to 8.5% by weight of yttrium oxide,

[0449] ≤ 0.4 wt %, such as in the range of 0.02 wt % to 0.2 wt %, such as in the range of 0.05 wt % to 0.1 wt % aluminum oxide,

[0450] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.0 wt%, such as in the range of 0.05 to 0.8 wt% of colored metal oxide,

[0451] 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.45 wt%, 0.10 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0452] All are based on the total weight of pre-sintered multi-layer dental mill blanks.

[0453] wherein the yttrium oxide comprises type II yttrium oxide as a sintering inhibitor,

[0454] The pre-sintered multi-layer dental mill blank comprises type II yttrium oxide in an amount of 0.1 wt% to 1.5 wt%, such as in the range of 0.2 wt% to 1.2 wt%, such as in the range of 0.4 wt% to 1.0 wt%, based on the total weight of the pre-sintered multi-layer dental mill blank, and

[0455] The weight amounts of the components are optionally selected to total 100 wt%.

[0456] In one embodiment, the pre-sintered multi-layer dental mill blank comprises (optionally consists essentially of or consists of):

[0457] 80% to 94% by weight, such as in the range of 85% to 93% by weight, such as in the range of 89% to 91% by weight of zirconium oxide,

[0458] ≤5 wt%, such as ≤3 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0459] 5.0% to 10.0% by weight, such as in the range of 6.0% to 9.0% by weight, such as in the range of 6.5% to 8.5% by weight of yttrium oxide,

[0460] ≤ 0.4 wt %, such as in the range of 0.02 wt % to 0.2 wt %, such as in the range of 0.05 wt % to 0.1 wt % aluminum oxide,

[0461] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.0 wt%, such as in the range of 0.05 to 0.8 wt% of colored metal oxide,

[0462] 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.45 wt%, 0.10 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0463] All are based on the total weight of pre-sintered multi-layer dental mill blanks.

[0464] wherein the yttrium oxide comprises type II yttrium oxide as a sintering inhibitor and the colored metal oxide comprises erbium oxide as a sintering inhibitor, and the pre-sintered multi-layer dental mill blank comprises the combination of type II yttrium oxide and erbium dioxide in an amount in the range of 0.1 wt.% to 2.0 wt.%, such as in the range of 0.2 wt.% to 1.5 wt.%, such as in the range of 0.4 wt.% to 1.2 wt.%, based on the total weight of the pre-sintered multi-layer dental mill blank.

[0465] The weight amounts of the components are optionally selected to total 100 wt%.

[0466] In one embodiment, the pre-sintered multi-layer dental mill blank comprises (optionally consists essentially of or consists of):

[0467] 80% to 94% by weight, such as in the range of 85% to 93% by weight, such as in the range of 89% to 91% by weight of zirconium oxide,

[0468] ≤5 wt%, such as ≤3 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0469] 5.0% to 10.0% by weight, such as in the range of 5.5% to 8.5% by weight, such as in the range of 6.0% to 8.0% by weight of type I yttrium oxide,

[0470] ≤ 0.4 wt %, such as in the range of 0.02 wt % to 0.2 wt %, such as in the range of 0.05 wt % to 0.1 wt % aluminum oxide,

[0471] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.0 wt%, such as in the range of 0.05 to 0.8 wt% of colored metal oxide,

[0472] 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.45 wt%, 0.10 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0473] 0.1 wt% to 2.0 wt%, such as in the range of 0.2 wt% to 1.5 wt%, such as in the range of 0.4 wt% to 1.2 wt% of a sintering inhibitor (e.g., a combination of type II yttrium oxide and erbium oxide),

[0474] All are based on the total weight of pre-sintered multi-layer dental mill blanks.

[0475] The weight amounts of the components are optionally selected to total 100 wt%.

[0476] 2.8 Composition of each layer

[0477] As described herein, each of the layers can contain different components in different weight amounts. It should be understood that the different components (including their weight amounts) of each of the layers as described herein are also disclosed in combination herein. It should also be understood that the different layers as described herein are also disclosed in combination herein.

[0478] As described above, a sintering activator can be combined with a sintering inhibitor in selected layers of a pre-sintered dental mill blank. By combining the sintering activator and the sintering inhibitor, the sintering curve of the ceramic material of the layer can be adjusted so that different portions of the sintering curve (related to different temperature ranges for sintering) are more aligned with corresponding portions of the sintering curve of the ceramic material of one or more of the other layers.

[0479] In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer, and when fully sintered by the rapid sintering method as described above, the representative test cross-section of the top layer and the representative test cross-section of the bottom layer each have a maximum sintering rate at the temperature T of the rapid sintering method, and the top layer (T TL ) and bottom layer (T BL ) differ by no more than 40° C. or by no more than 25° C. In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer, each of the representative test cross-sections having a maximum sintering rate at the temperature T of the rapid sintering method when fully sintered by the rapid sintering method as described above, and wherein the temperature T of each of the layers differs by no more than 40° C. or by no more than 25° C.

[0480] In one embodiment, the pre-sintered multi-layer dental mill blank comprises

[0481] Top floor,

[0482] bottom layer, and

[0483] At least one intermediate layer,

[0484] Each layer contains a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof), and

[0485] The base layer, and optionally each of the at least one intermediate layer, comprises a sintering inhibitor (eg, type II yttrium oxide).

[0486] In one embodiment, the pre-sintered multi-layer dental mill blank comprises

[0487] Top floor,

[0488] bottom layer, and

[0489] At least one intermediate layer,

[0490] each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer,

[0491] Each layer contains a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0492] Optionally, each layer comprises a colored metal oxide, and

[0493] The base layer, and optionally each of the at least one intermediate layer, comprises a sintering inhibitor (eg, type II yttrium oxide).

[0494] The yttrium oxide content may increase from the bottom layer to the top layer such that the bottom layer has a lower yttrium oxide content than at least one intermediate layer and at least one intermediate layer has a lower yttrium oxide content than the top layer. Preferably, the yttrium oxide content of the layers increases layer by layer from the bottom layer to the top layer.

[0495] In one embodiment, the pre-sintered multi-layer dental mill blank comprises

[0496] Top floor,

[0497] bottom layer, and

[0498] At least one intermediate layer,

[0499] Each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer,

[0500] Each layer contains a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0501] Optionally, each layer comprises a colored metal oxide, and

[0502] The base layer, and optionally each of the at least one intermediate layer, comprises a sintering inhibitor (eg, type II yttrium oxide).

[0503] In one embodiment, the top layer comprises (optionally consists essentially of or consists of):

[0504] 80% to 92% by weight, such as in the range of 85% to 91% by weight, such as in the range of 87% to 90% by weight of zirconium oxide,

[0505] ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0506] 7.0 to 13.0 wt%, such as in the range of 8.0 to 12.0 wt%, such as in the range of 9.0 to 11.0 wt% yttrium oxide,

[0507] <0.01 wt.% aluminum oxide,

[0508] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide,

[0509] 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.10 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0510] Each is based on the total weight of the top layer, wherein the weight amounts of the components are optionally selected to total 100 wt%.

[0511] In one embodiment, the top layer comprises (optionally consists essentially of or consists of):

[0512] 80% to 92% by weight, such as in the range of 85% to 91% by weight, such as in the range of 87% to 90% by weight of zirconium oxide,

[0513] ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0514] 7.0 to 13.0 wt%, such as in the range of 8.0 to 12.0 wt%, such as in the range of 9.0 to 11.0 wt% yttrium oxide,

[0515] <0.01 wt.% aluminum oxide,

[0516] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide,

[0517] 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.10 wt% to 0.30 wt% of a sintering activator which is zinc oxide, gallium oxide, or a combination thereof,

[0518] Each is based on the total weight of the top layer, wherein the weight amounts of the components are optionally selected to total 100 wt%.

[0519] In one embodiment, the bottom layer comprises (optionally consists essentially of or consists of):

[0520] 85 to 94 wt%, such as in the range of 88 to 94 wt%, such as in the range of 90 to 92 wt% zirconium oxide,

[0521] ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0522] 0.01 to 0.50 wt%, such as in the range of 0.02 to 0.40 wt%, such as in the range of 0.05 to 0.20 wt% alumina,

[0523] 4.0 to 9.0 wt%, such as in the range of 5.0 to 8.0 wt%, such as in the range of 5.5 to 7.5 wt% of yttrium oxide,

[0524] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide,

[0525] 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.05 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0526] Each is based on the total weight of the base layer, wherein the weight amounts of the components are optionally selected to total 100 wt%.

[0527] In one embodiment, the bottom layer comprises (optionally consists essentially of or consists of):

[0528] 85 to 94 wt%, such as in the range of 88 to 94 wt%, such as in the range of 90 to 92 wt% zirconium oxide,

[0529] ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0530] 0.01 to 0.50 wt%, such as in the range of 0.02 to 0.40 wt%, such as in the range of 0.05 to 0.20 wt% alumina,

[0531] 4.0 to 9.0 wt%, such as in the range of 5.0 to 8.0 wt%, such as in the range of 5.5 to 7.5 wt% of yttrium oxide,

[0532] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide,

[0533] 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.05 wt% to 0.30 wt% of a sintering activator which is zinc oxide, gallium oxide, or a combination thereof,

[0534] Each is based on the total weight of the base layer, wherein the weight amounts of the components are optionally selected to total 100 wt%.

[0535] The yttrium oxide of the bottom layer may include type II yttrium oxide as a sintering inhibitor, and the bottom layer may include type II yttrium oxide in an amount in the range of 0.4 wt% to 1.5 wt%, such as in the range of 0.6 wt% to 1.2 wt%, such as in the range of 0.8 wt% to 1.1 wt%, based on the total weight of the bottom layer.

[0536] In one embodiment, each of the at least one intermediate layer comprises (optionally consists essentially of or consists of):

[0537] 82 to 94 wt%, such as in the range of 85 to 93 wt%, such as in the range of 87 to 92 wt% zirconium oxide,

[0538] ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0539] 0.01 to 0.50 wt%, such as in the range of 0.02 to 0.20 wt%, such as in the range of 0.02 to 0.15 wt% alumina,

[0540] 5.0 to 11.0 wt%, such as in the range of 6.0 to 10.5 wt%, such as in the range of 6.5 to 10.0 wt% yttrium oxide,

[0541] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide,

[0542] 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.05 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0543] Each is based on the total weight of the respective layer of the at least one intermediate layer, wherein the weight amounts of the components are optionally selected to total 100 wt%.

[0544] In one embodiment, each of the at least one intermediate layer comprises (optionally consists essentially of or consists of):

[0545] 82 to 94 wt%, such as in the range of 85 to 93 wt%, such as in the range of 87 to 92 wt% zirconium oxide,

[0546] ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0547] 0.01 to 0.50 wt%, such as in the range of 0.02 to 0.20 wt%, such as in the range of 0.02 to 0.15 wt% alumina,

[0548] 5.0 to 11.0 wt%, such as in the range of 6.0 to 10.5 wt%, such as in the range of 6.5 to 10.0 wt% yttrium oxide,

[0549] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide,

[0550] 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.05 wt% to 0.30 wt% zinc oxide, gallium oxide, or a combination thereof,

[0551] Each is based on the total weight of the respective layer of the at least one intermediate layer, wherein the weight amounts of the components are optionally selected to total 100 wt%.

[0552] The yttrium oxide in each of the at least one intermediate layer may contain type II yttrium oxide as a sintering inhibitor, and each of the at least one intermediate layer may contain type II yttrium oxide in an amount in the range of 0.02 wt.% to 1.0 wt.%, such as in the range of 0.05 wt.% to 1.0 wt.%, such as in the range of 0.05 wt.% to 0.6 wt.%, based on the total weight of the corresponding layer of the at least one intermediate layer.

[0553] In one embodiment, the pre-sintered multi-layer dental mill blank comprises the following layers:

[0554] Top floor L4,

[0555] Middle layer L3,

[0556] the middle layer L2, and

[0557] Bottom layer L1,

[0558] And said layers L4 to L1 comprise the components as defined in Table I herein below, wherein the indicated weight amounts are based on the total weight of the respective layer.

[0559] Table I:

[0560]

[0561] In one embodiment, the pre-sintered multi-layer dental mill blank comprises the following layers:

[0562] Top floor L4,

[0563] Middle layer L3,

[0564] the middle layer L2, and

[0565] Bottom layer L1,

[0566] And said layers L4 to L1 comprise the components as defined below in Table 1b herein, wherein the indicated weight amounts are based on the total weight of the respective layer.

[0567] Table Ib:

[0568]

[0569] In one embodiment, the pre-sintered multi-layer dental mill blank comprises the following layers:

[0570] Top floor L4,

[0571] Middle layer L3,

[0572] the middle layer L2, and

[0573] Bottom layer L1,

[0574] And said layers L4 to L1 comprise the components as defined below in Table II herein, wherein the indicated weight amounts are based on the total weight of the respective layer.

[0575] Table II:

[0576]

[0577] In one embodiment, the pre-sintered multi-layer dental mill blank comprises the following layers:

[0578] Top floor L4,

[0579] Middle layer L3,

[0580] the middle layer L2, and

[0581] Bottom layer L1,

[0582] And said layers L4 to L1 comprise the components as defined below in Table III herein, wherein the indicated weight amounts are based on the total weight of the respective layer.

[0583] Table III:

[0584]

[0585] In one embodiment, the pre-sintered multi-layer dental mill blank comprises the following layers:

[0586] Top floor L4,

[0587] Middle layer L3,

[0588] the middle layer L2, and

[0589] Bottom layer L1,

[0590] And said layers L4 to L1 comprise the components as defined in Table IV herein below, wherein the indicated weight amounts are based on the total weight of the respective layer.

[0591] Table IV:

[0592]

[0593] The weight amounts of the components present in each of layers L1 to L4 as defined in any of Tables I, Ib, II, III, and IV may be selected to total 100 weight percent.

[0594] Layers L4 to L1 as defined in any one of Tables I to IV may have an increasing yttrium oxide content from layer L1 to layer L4, such that layer L1 has a lower yttrium oxide content than layers L2 and L3, and layers L2 and L3 have a lower yttrium oxide content than layer L4. Layers L4 to L1 as defined in any one of Tables I, Ib, II, III, and IV may have an increasing yttrium oxide content from layer L1 to layer L4.

[0595] Layers L4 through L1 as defined in any of Table I, Table Ib, Table II, Table III, and Table IV may consist essentially of or may consist of the components defined in the respective table.

[0596] The colored metal oxide present in layer L4 to layer L1 as defined in any one of Table I, Table Ib, Table II, Table III, and Table IV may contain erbium oxide as a sintering inhibitor.

[0597] The yttrium oxide present in layer L3 to layer L1 as defined in any one of Table I, Table Ib, Table II, Table III and Table IV may contain type II yttrium oxide as a sintering inhibitor, and optionally, wherein

[0598] the intermediate layer L3 contains type II yttrium oxide in an amount by weight ranging from 0.02 wt % to 0.6 wt %, from 0.05 wt % to 0.4 wt %, or from 0.06 wt % to 0.2 wt %, based on the total weight of the intermediate layer L3,

[0599] the intermediate layer L2 contains type II yttrium oxide in an amount by weight ranging from 0.1 wt % to 1.0 wt %, from 0.2 wt % to 0.8 wt %, or from 0.4 wt % to 0.6 wt %, based on the total weight of the intermediate layer L2,

[0600] The bottom layer L1 contains type II yttrium oxide in an amount by weight ranging from 0.4 wt% to 1.5 wt%, from 0.6 wt% to 1.2 wt%, or from 0.8 wt% to 1.1 wt%, based on the total weight of the bottom layer L1, and

[0601] The content of type II yttrium oxide decreases layer by layer from layer L3 to layer L1.

[0602] Any of the layers may contain unavoidable impurities (eg, SiO 2 , CaO, TiO 2 , or Na 2 O), for example, in a combined amount of less than 0.1 wt %, based on the total weight of the corresponding layer.

[0603] 3. Form, structure and layering

[0604] The pre-sintered multilayer dental mill blank according to the invention comprises a top layer, a bottom layer and at least one intermediate layer.

[0605] The number of at least one intermediate layer can be in the range of 1 to 10 intermediate layers, such as in the range of 1 to 5 intermediate layers. For example, the pre-sintered multi-layer dental mill blank can comprise one, two or three intermediate layers. In one embodiment, the pre-sintered multi-layer dental mill blank comprises two intermediate layers.

[0606] For example, a pre-sintered multi-layer dental mill blank may comprise the following layers: a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1. The numbering of layers L4 to L1 should be understood as defining the stacking order of the layers in the pre-sintered multi-layer dental mill blank (i.e., the order of layers L4 to L1 is L4, then L3, then L2, then L1). In this context, the term "comprising" should be understood to mean that the pre-sintered multi-layer dental mill blank may contain one or more additional intermediate layers, for example, between layer L4 and layer L3, between layer L3 and layer L2, and so on. A pre-sintered multi-layer dental mill blank may consist of the following layers: a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1. In this context, the term "consisting of" should be understood to mean that the pre-sintered multi-layer dental mill blank only contains the layers L4 to L1.

[0607] The layers of the pre-sintered multilayer dental mill blank are not particularly limited in size and shape, as long as the dental mill blank is suitable for use in the preparation of dental restoration precursors (e.g., using CAD / CAM methods). One or more layers may be non-planar. For example, one or more layers may have one or two faces (e.g., an interface between two layers or an outer surface depending on the position of the layer in the mill blank) that are curved (e.g., having a positive or negative curvature (e.g., convex or concave)). One or more of the layers may have a height that increases uniformly or non-uniformly (e.g., in a tapered manner) over at least a portion of the layer.

[0608] One or more of the layers (optionally all of the layers) may be substantially planar. In this context, "substantially planar" means that a layer is planar, allowing a tolerance of 5% of the average thickness of the layer. One or more of the layers (optionally all of the layers) may be substantially planar over at least 70%, at least 80%, at least 90% or at least 95% of the width and length relative to the total width and length (x-direction and y-direction) of the layer. Due to the inevitable imperfect pressing of the green body, a layer that is substantially planar over a major part of its width and length is likely to show curvature on the outer part of the surface located on the dental mill blank. Figure 2 This curvature can be seen in the comparative mill blank on the left.

[0609] The layers of the pre-sintered multi-layer dental mill blank may be arranged such that the boundaries of the layers are substantially parallel to each other.

[0610] Each layer of the pre-sintered multilayer dental mill blank can have a specific height relative to the total height of the dental mill blank. The total height of the dental mill blank can be understood as the size of the dental mill blank in the stacking direction (z-direction) of the layers. For example, for rectangular or disc-shaped dental mill blanks, etc., the total height can be determined as the distance between the outer surface of the top layer and the relative outer surface of the bottom layer, and the vertical line intersects all layers of the dental mill blank. The height of a layer should be understood as the maximum height of the layer in the stacking direction (z-direction) of the layer. This is independent of whether the relative height or absolute height is defined in this article. Therefore, the definition of layer height as used herein (e.g., relative height or absolute height) does not necessarily mean that the height of the layer is constant, although this is possible.

[0611] Each of the layers may have a substantially constant height. "Substantially constant height" means that the height of the layer does not vary by more than 5% relative to the average height of the layer.

[0612] The bottom layer may have a height of at least 30%, at least 40%, at least 45%, at least 50%, or at least 52% relative to the total height of the pre-sintered multi-layer dental mill blank. The bottom layer may have a height of at most 75%, at most 70%, at most 68%, or at most 66% relative to the total height of the pre-sintered multi-layer dental mill blank. The bottom layer may have a height in the range of 30% to 75%, 40% to 75%, 45% to 70%, 50% to 68%, or 52% to 66% relative to the total height of the pre-sintered multi-layer dental mill blank. In one embodiment, the bottom layer has a height of 52% to 66% relative to the total height of the pre-sintered multi-layer dental mill blank.

[0613] The sum of the heights of the bottom layer and the adjacent intermediate layers can be at least 55%, at least 60%, or at least 65% of the total height of the pre-sintered multi-layer dental mill blank. The sum of the heights of the bottom layer and the adjacent intermediate layers can be at most 85%, at most 80%, or at most 75% of the total height of the pre-sintered multi-layer dental mill blank. The sum of the heights of the bottom layer and the adjacent intermediate layers can be in the range of 55% to 85%, 60% to 80%, or 65% to 75% of the total height of the pre-sintered multi-layer dental mill blank. In one embodiment, the sum of the heights of the bottom layer and the adjacent intermediate layers can be in the range of 60% to 80% of the total height of the pre-sintered multi-layer dental mill blank.

[0614] The top layer may have a height of at least 8%, at least 10%, at least 12%, at least 15%, or at least 17% relative to the total height of the pre-sintered multi-layer dental mill blank. The top layer may have a height of at most 35%, at most 30%, at most 28%, at most 25%, or at most 23% relative to the total height of the pre-sintered multi-layer dental mill blank. The top layer may have a height in the range of 8% to 35%, 10% to 30%, 12% to 28%, 15% to 25%, or 17% to 23% relative to the total height of the pre-sintered multi-layer dental mill blank. In one embodiment, the top layer has a height in the range of 17% to 23% relative to the total height of the pre-sintered multi-layer dental mill blank.

[0615] Each of the at least one intermediate layer may have a height of at least 2%, at least 4%, at least 6%, or at least 8% relative to the total height of the pre-sintered multi-layer dental mill blank. Each of the at least one intermediate layer may have a height of at most 25%, at most 20%, at most 15%, or at most 12% relative to the total height of the pre-sintered multi-layer dental mill blank. Each of the at least one intermediate layer may have a height in the range of 2% to 25%, 4% to 20%, 6% to 15%, or 8% to 12% relative to the total height of the pre-sintered multi-layer dental mill blank. In one embodiment, each of the at least one intermediate layer has a height in the range of 8% to 12% relative to the total height of the pre-sintered multi-layer dental mill blank.

[0616] The combined intermediate layer may have a height of at least 5%, at least 10%, at least 14%, or at least 16% relative to the total height of the pre-sintered multi-layer dental mill blank. The combined intermediate layer may have a height of at most 40%, at most 30%, at most 26%, or at most 25% relative to the total height of the pre-sintered multi-layer dental mill blank. The combined intermediate layer may have a height in the range of 5% to 40%, 10% to 30%, 14% to 26%, or 16% to 25% relative to the total height of the pre-sintered multi-layer dental mill blank. In one embodiment, the combined intermediate layer has a height in the range of 16% to 25% relative to the total height of the pre-sintered multi-layer dental mill blank.

[0617] According to one embodiment, the pre-sintered multi-layer dental mill blank consists of the following layers:

[0618] a top layer L4 having a height in the range of 12% to 28%, such as in the range of 15% to 25%, such as in the range of 17.5% to 23.5%,

[0619] an intermediate layer L3 having a height in the range of 4% to 20%, such as in the range of 6% to 15%, such as in the range of 8.5% to 12%,

[0620] an intermediate layer L2 having a height in the range of 4% to 20%, such as in the range of 6% to 15%, such as in the range of 8.5% to 12%, and

[0621] a bottom layer L1 having a height in the range of 45% to 70%, such as in the range of 50% to 68%, such as in the range of 52.5% to 65.5%,

[0622] The heights of the layers are all relative to the total height of the pre-sintered multilayer dental mill blank and are selected so as to sum to 100%.

[0623] Additionally or alternatively, each of the layers of the pre-sintered dental mill blank may be defined by an absolute height, for example expressed in millimeters.

[0624] The bottom layer can have a height of at least 1 mm, at least 5 mm, at least 7 mm, or at least 9 mm. The bottom layer can have a height of at most 20 mm, at most 15 mm, at most 12 mm, or at most 3 mm. The bottom layer can have a height in the range of 1 mm to 20 mm, 5 mm to 20 mm, 7 mm to 15 mm, 9 mm to 12 mm. The top layer can have a height of at least 1 mm, at least 2 mm, or at least 3 mm. The top layer can have a height of at most 8 mm, at most 5 mm, or at most 4 mm. The top layer can have a height in the range of 1 mm to 8 mm, 2 mm to 5 mm, or 3 mm to 4 mm. Each of the at least one intermediate layer can have a height in the range of 1 mm to 3 mm, such as in the range of 1.5 mm to 2.0 mm. The combined intermediate layer can have a height of at least 2 mm, at least 3 mm, at most 6 mm, or at most 4 mm, such as in the range of 2 mm to 6 mm or 3 mm to 4 mm.

[0625] According to one embodiment, the pre-sintered multi-layer dental mill blank comprises or consists of the following layers:

[0626] a top layer L4 having a height in the range of 2 mm to 5 mm (e.g., 3 mm to 4 mm),

[0627] an intermediate layer L3 having a height in the range of 1 mm to 3 mm (eg, about 1.5 mm or about 2 mm),

[0628] an intermediate layer L2 having a height in the range of 1 mm to 3 mm (eg, about 1.5 mm or about 2 mm),

[0629] The bottom layer L1 has a height in the range of 1 mm to 20 mm (eg, in the range of 1 mm to 3 mm or in the range of 7 mm to 15 mm).

[0630] According to one embodiment, the pre-sintered multi-layer dental mill blank comprises or consists of the following layers:

[0631] a top layer L4 having a height in the range of 2 mm to 5 mm (e.g., 3 mm to 4 mm),

[0632] an intermediate layer L3 having a height in the range of 1 mm to 3 mm (eg, about 1.5 mm or about 2 mm),

[0633] an intermediate layer L2 having a height in the range of 1 mm to 3 mm (eg, about 1.5 mm or about 2 mm),

[0634] The bottom layer L1 has a height in the range of 5 mm to 20 mm (eg, in the range of 7 mm to 15 mm).

[0635] Pre-sintered multilayer dental milling blank is not particularly limited in its shape or its size, as long as it is suitable for preparing a dental restoration precursor (for example, using a CAD / CAM method). Pre-sintered multilayer dental milling blank can have but is not limited to the form of a rectangular block, a disk, a cylinder, a dental preform (for example, abutment preform or tooth sector), a cone, a cone segment, a pyramid or a pyramid segment. In one embodiment, the pre-sintered multilayer dental milling blank has the form of a disk, a cylinder or a rectangular block. For example, the pre-sintered multilayer dental milling blank can be but is not limited to a height in the range of 8 mm to 30 mm (for example, approximately 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, 25 mm), such as in the range of 14 mm to 22 mm, and a diameter in the range of 70 mm to 150 mm, such as in the range of 90 mm to 110 mm, such as a disk of about 98 mm.

[0636] The pre-sintered multi-layer dental mill blank can be porous or have a porous structure, and in particular can be open porous or have an open porous structure. The density of the pre-sintered multi-layer dental mill blank can be at least 45%, at least 50%, at least 52%, at most 70%, at most 60%, at most 55% relative to its theoretical density, such as in the range of 45% to 70% (e.g., 45% to 55%), 50% to 60% or 52% to 55% (e.g., about 52% or about 53%). In one embodiment, the density of the pre-sintered multi-layer dental mill blank is in the range of 45% to 55% relative to its theoretical density. In one embodiment, the density of the pre-sintered multi-layer dental mill blank is equal to or less than 53% (e.g., 45% to 53% or 45% to 52%) relative to its theoretical density.

[0637] The pre-sintered multi-layer dental mill blank can be obtained by pre-sintering a green body of the pre-sintered multi-layer dental mill blank at a maximum pre-sintering temperature of at least 700° C., at least 750° C., at least 800° C., at least 825° C., 1100° C., at most 1000° C., at most 950° C., at most 900° C., such as in the range of 700° C. to 1100° C., in the range of 750° C. to 1000° C., in the range of 800° C. to 950° C., or in the range of 825° C. to 900° C. In one embodiment, the pre-sintered multi-layer dental mill blank can be obtained by pre-sintering a green body of the pre-sintered multi-layer dental mill blank at a maximum pre-sintering temperature in the range of 800° C. to 950° C., such as in the range of 825° C. to 900° C. The maximum pre-sintering temperature can be achieved by heating the green body for a period of at least 30 hours or at least 40 hours, such as in the range of 40 hours to 50 hours. Therefore, heating is typically performed using a low heating rate (e.g., in the range of 0.05 K / min to 2 K / min or in the range of 0.1 K / min to 1.5 K / min). Heating can be performed stepwise using different heating steps at different heating rates (in the range of 0.05 K / min to 2 K / min or 0.1 K / min to 1.5 K / min). The maximum pre-sintering temperature can be maintained for a period of time in the range of 1 hour to 5 hours, such as in the range of 2 hours to 3 hours.

[0638] The green body may be a compacted green body, such as a pressed green body (eg, a uniaxially pressed green body) obtainable using a compaction pressure in the range of 200 MPa to 400 MPa, such as in the range of 250 MPa to 350 MPa.

[0639] One embodiment of the present invention provides a pre-sintered multi-layer dental mill blank obtainable by a method for preparing a pre-sintered multi-layer dental mill blank according to one embodiment of the present invention. The method will be described in more detail in the following sections.

[0640] II. Method for Preparing Pre-Sintered Multilayer Dental Mill Blanks

[0641] One aspect of the present invention provides a method for preparing a pre-sintered multi-layer dental mill blank, the method comprising the steps of:

[0642] a) providing three yttria-stabilized zirconium oxide powders P1 to P3, powder P1 having an yttria content in the range of 4.5% to 6.1% by weight, powder P2 having an yttria content in the range of 6.2% to 7.9% by weight, and powder P3 having an yttria content in the range of 8.0% to 11.0% by weight,

[0643] b) preparing a green body comprising:

[0644] The top powder layer of powder P3,

[0645] at least one intermediate powder layer of a powder mixture chosen from a mixture of powders P2 / P3 and a mixture of powders P1 / P2,

[0646] a bottom powder layer of powder P1 or a mixture of powders P1 / P2,

[0647] c) pre-sintering the green body to provide a pre-sintered multi-layer dental mill blank.

[0648] It has been found that pre-sintered multilayer dental mill blanks based on a mixed pattern of powders P1 to P3 according to a method according to an embodiment of the present invention may be particularly suitable for preparing dental restorations having a desired optical appearance and a relatively large difference in one or more properties between the incisional or occlusal area and the dentin area of ​​the dental restoration.

[0649] The expression "top powder layer of powder P3" is to be understood as meaning that the top powder layer does not contain yttria-stabilized zirconia powder having a different yttria content than powder P3. This does not exclude that powder P3 may be a blend of different yttria-stabilized zirconia powders having an yttria content in the range of 8.0% to 11.0% by weight. The expressions "middle powder layer of a mixture of powders P2 / P3," "bottom powder layer of powder P1," etc. are to be understood in the same manner, mutatis mutandis.

[0650] In one embodiment, the green body consists of:

[0651] The top powder layer of powder P3,

[0652] at least one intermediate powder layer of a powder mixture chosen from a mixture of powders P2 / P3 and a mixture of powders P1 / P2,

[0653] Bottom powder layer of powder P1 or a mixture of powders P1 / P2.

[0654] In one embodiment, the green body comprises or consists of:

[0655] The top powder layer of powder P3,

[0656] An intermediate powder layer of a mixture of powders P2 / P3,

[0657] An intermediate powder layer of a mixture of powders P1 / P2,

[0658] Bottom powder layer of powder P1.

[0659] Each of powders P1 to P3 can have a combined amount of zirconium oxide, yttrium oxide, and hafnium dioxide of at least 95%, at least 98%, at least 99%, or in a range of 95% to 99.9%, 98% to 99.9%, or 99% to 99.8%, based on the total weight of the respective powder. Powders P1 and / or P2 can include aluminum oxide in an amount of at most 0.40%, at most 0.30%, or at most 0.20%, or in a range of 0.01% to 0.40%, 0.02% to 0.30%, or 0.04% to 0.20%, based on the total weight of the respective powder. Powder P3 can include aluminum oxide in an amount of less than 0.05%, such as less than 0.02%, or less than 0.01%, based on the total weight of powder P3.

[0660] The yttrium oxide content (in wt %) of powders P1 and P2 and the yttrium oxide content (in wt %) of powders P2 and P3 can differ by at least 0.7 percentage points, at least 1.0 percentage points, at least 1.2 percentage points, at most 3.0 percentage points, at most 2.8 percentage points, at most 2.5 percentage points, from 0.7 percentage points to 3.0 percentage points, from 1.0 percentage points to 2.8 percentage points, or from 1.2 percentage points to 2.5 percentage points. Powder P1 can have an yttrium oxide content in the range of 4.9 wt % to 6.0 wt %. Powder P2 can have an yttrium oxide content in the range of 6.5 wt % to 7.6 wt %. Powder P3 can have an yttrium oxide content in the range of 9.0 wt % to 10.5 wt %.

[0661] The mixture of powders P2 / P3 may contain powders P2 and P3 in a weight ratio [powder P2:powder P3] within a range of 10:90 to 40:60, 15:85 to 35:65, or 20:80 to 30:70. The mixture of powders P1 / P2 may contain powders P1 and P2 in a weight ratio [powder P1:powder P2] within a range of 10:90 to 40:60, 15:85 to 35:65, or 20:80 to 30:70. In one embodiment, the mixture of powders P2 / P3 may contain powders P2 and P3 in a weight ratio [powder P2: powder P3] in the range of 10:90 to 40:60, in the range of 15:85 to 35:65, or in the range of 20:80 to 30:70, and the mixture of powders P1 / P2 may contain powders P1 and P2 in a weight ratio [powder P1: powder P2] in the range of 10:90 to 40:60, in the range of 15:85 to 35:65, or in the range of 20:80 to 30:70.

[0662] The method may include adding one or more additives to powders P1 to P3 or a mixture thereof, the additives being selected from the group consisting of a sintering inhibitor precursor, a sintering inhibitor precursor, and a coloring additive. Thus, powders P1 to P3 or a mixture thereof present in different powder layers of the green body may be treated, for example surface treated, with one or more additives selected from the group consisting of a sintering inhibitor precursor, a sintering inhibitor precursor, and a coloring additive. The one or more additives may be added in the form of an aqueous suspension, typically an aqueous solution.

[0663] One or more additives can be added at different stages of the process. For example, one or more additives can be added to powders P1 to P3 before preparing the powder mixture of powders P1 / P2 and powders P2 / P3. However, it is possible to first prepare the powder mixture of powders P1 / P2 and powders P2 / P3 and then add the one or more additives to the mixture of powders P1 / P2 and powders P2 / P3 and powders P1 and / or P3. In one embodiment, one or more additives are added to powders P1 to P3 before preparing the powder mixture of powders P1 / P2 and powders P2 / P3.

[0664] The method may include adding a sintering activator precursor to at least powder P3 or a mixture thereof. The method may include adding the sintering activator precursor to powders P1 to P3 or a mixture thereof, typically before preparing the green body. Thus, powders P1 to P3 or a mixture thereof present in different powder layers of the green body may have been treated with the sintering activator precursor, such as surface treated. The sintering activator precursor may be added to the powders in the form of an aqueous suspension, typically an aqueous solution.

[0665] Thus, each of the powder layers of the green body can contain a sintering activator precursor. The sintering activator precursor can be added so that the powder layers have different weight contents of the sintering activator precursor. For example, the top powder layer has a higher weight content of the sintering activator precursor than the weight content of the sintering activator precursor in the bottom layer. The weight content of the sintering activator precursor can increase layer by layer from the bottom powder layer to the top powder layer. Thus, the weight amount of the sintering activator precursor added to the powder can increase from P1 to P2 and then to P3.

[0666] Each of the powder layers of the green body can contain a sintering activator precursor in an amount suitable for achieving a sintering activator in each of the layers of the pre-sintered multi-layer dental mill blank prepared by the method, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental mill blank. Based on the target amount of sintering activator, one skilled in the art can calculate the amount of sintering activator precursor that needs to be included in the powder layer for a given pair of sintering activator precursor and sintering activator (e.g., for a pair of zinc nitrate as a sintering activator precursor and zinc oxide as a sintering activator) to achieve the desired amount of sintering activator.

[0667] The sintering activator precursor can be a metal salt, which can be converted into a metal oxide during the pre-sintering step of the method to provide a metal oxide as a sintering activator. The metal salt can be a water-soluble metal salt. The metal salt can be an organic acid metal salt or an inorganic metal salt. Suitable inorganic metal salts can be, but are not limited to, metal phosphates, metal nitrates, metal sulfates, or metal halides.

[0668] In one embodiment, the sintering activator precursor is a zinc salt, a gallium salt, or a combination thereof. Thus, the sintering activator precursor can be a zinc salt, a gallium salt, or a combination thereof, which can be converted into a sintering activator as zinc oxide, gallium oxide, or a combination thereof during the pre-sintering step of the method. In one embodiment, the method comprises adding a sintering activator precursor to powders P1 to P3 or a mixture thereof, the sintering activator precursor being a zinc salt, a gallium salt, or a combination thereof.

[0669] In a preferred embodiment, the sintering activator precursor is a zinc salt. The zinc salt can be an inorganic zinc salt, such as zinc nitrate. The zinc salt can be water-soluble.

[0670] Each of the powder layers of the green body may contain a sintering activator precursor as a zinc salt, a gallium salt, or a combination thereof in an amount by weight of at least 0.02 wt%, at least 0.05 wt%, at least 0.10 wt%, at most 0.8 wt%, at most 0.50 wt%, at most 0.30 wt%, or in the range of 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.50 wt%, or 0.10 wt% to 0.30 wt%, based on the total weight of the corresponding layer of the pre-sintered multi-layer dental mill blank, the weight amount of which is suitable to obtain a sintering activator as zinc oxide, gallium oxide, or a combination thereof in each of the layers of the pre-sintered multi-layer dental mill blank produced by the method.

[0671] The method may comprise adding a sintering inhibitor precursor to at least powder P1 or a mixture thereof. The method may comprise adding a sintering inhibitor precursor to powders P1 and P2 or a mixture thereof, typically before preparing the green body. Thus, powders P1 and P2 or a mixture thereof present in different powder layers of the green body may be treated, for example surface treated, with a sintering inhibitor precursor. The expression "adding a sintering inhibitor precursor to powders P1 and P2 or a mixture thereof" should be understood in a broad sense, as it encompasses the alternative of adding one or more additives to the individual powders P1 and P2 or to any mixture comprising one of powders P1 or P2, including a mixture of powders P2 / P3. The sintering inhibitor precursor may be added to the powders in the form of an aqueous suspension, typically an aqueous solution.

[0672] Thus, the bottom powder layer of the green body, and optionally, the intermediate powder layer adjacent to the bottom layer, can contain a sintering inhibitor precursor. The sintering inhibitor precursor can be added so that the powder layers have different weight contents of the sintering inhibitor precursor. For example, the bottom powder layer can have a higher weight content of the sintering inhibitor precursor than the weight content of the sintering inhibitor precursor in the top powder layer. The weight content of the sintering inhibitor precursor can decrease from the bottom powder layer to the top powder layer. Thus, the weight amount of the sintering inhibitor precursor added to the powder can decrease from P1 to P2 to P3.

[0673] The bottom powder layer of powder P1 of the green body may contain a sintering inhibitor precursor in an amount by weight of at least 0.4 wt.%, at least 0.6 wt.%, at least 0.8 wt.%, at most 2.5 wt.%, at most 2.0 wt.%, at most 1.5 wt.%, or in the range of 0.4 wt.% to 2.5 wt.%, 0.6 wt.% to 2.0 wt.%, or 0.8 wt.% to 1.5 wt.%, based on the total weight of the bottom layer of the pre-sintered multi-layer dental mill blank, which is an amount suitable for obtaining a sintering inhibitor in the bottom layer of the pre-sintered multi-layer dental mill blank produced by the method.

[0674] The intermediate powder layer of the mixture of powders P1 / P2 of the green body may contain a sintering inhibitor precursor in an amount by weight of at least 0.02 wt.-%, at least 0.05 wt.-%, at most 2.0 wt.-%, at most 1.5 wt.-%, at most 1.2 wt.-%, or in a range of 0.02 wt.-% to 2.0 wt.-%, 0.05 wt.-% to 1.5 wt.-%, or 0.05 wt.-% to 1.2 wt.-%, based on the total weight of the corresponding intermediate layer of the pre-sintered multilayer dental mill blank, the weight amount being suitable for obtaining a sintering inhibitor in the corresponding intermediate layer of the pre-sintered multilayer dental mill blank produced by the method.

[0675] The intermediate powder layer of the mixture of powders P2 / P3 of the green body may contain a sintering inhibitor precursor in an amount by weight of at least 0.02 wt.-%, at least 0.05 wt.-%, at most 2.0 wt.-%, at most 1.5 wt.-%, at most 1.2 wt.-%, or in a range of 0.02 wt.-% to 2.0 wt.-%, 0.05 wt.-% to 1.5 wt.-%, or 0.05 wt.-% to 1.2 wt.-%, based on the total weight of the corresponding intermediate layer of the pre-sintered multilayer dental mill blank, the weight amount being suitable for obtaining a sintering inhibitor in the corresponding intermediate layer of the pre-sintered multilayer dental mill blank produced by the method.

[0676] The sintering inhibitor precursor can be a metal salt, which can be converted into a metal oxide in the pre-sintering step of the method to provide a metal oxide as a sintering inhibitor. The metal salt can be a water-soluble metal salt. The metal salt can be an organic acid metal salt or an inorganic metal salt. Suitable inorganic metal salts can be, but are not limited to, metal phosphates, metal nitrates, metal sulfates, or metal halides. The metal salt can be a yttrium salt, an erbium salt, a lanthanum salt, a ytterbium salt, a thulium salt, or any combination thereof. In one embodiment, the sintering inhibitor is a yttrium salt, an erbium salt, a lanthanum salt, or any combination thereof, optionally, the sintering inhibitor is a yttrium salt, an erbium salt, or a combination thereof.

[0677] In a preferred embodiment, the sintering inhibitor precursor is a yttrium salt, optionally in combination with an erbium salt. Thus, the sintering inhibitor precursor can be a yttrium salt that can be converted into a sintering inhibitor as type II yttrium oxide during the pre-sintering step of the method. In one embodiment, the method comprises adding the sintering inhibitor precursor to powders P1 and P2, or a mixture thereof, the sintering inhibitor precursor being a yttrium salt. The yttrium salt can be an inorganic yttrium salt, such as yttrium nitrate. The yttrium salt can be water-soluble.

[0678] The bottom powder layer of powder P1 of the green body may contain a sintering inhibitor precursor as a yttrium salt in an amount by weight of at least 0.4 wt.%, at least 0.6 wt.%, at least 0.8 wt.%, at most 1.5 wt.%, at most 1.2 wt.%, at most 1.1 wt.%, or in the range of 0.4 wt.% to 1.5 wt.%, 0.6 wt.% to 1.2 wt.%, or 0.8 wt.% to 1.1 wt.%, based on the total weight of the bottom layer of the pre-sintered multi-layer dental mill blank, the amount of which is suitable for obtaining a sintering inhibitor as type II yttrium oxide in the bottom layer of the pre-sintered multi-layer dental mill blank produced by the method.

[0679] The intermediate powder layer of the mixture of powders P1 / P2 of the green body may contain a sintering inhibitor precursor as a yttrium salt in an amount by weight of at least 0.1 wt. %, at least 0.2 wt. %, at least 0.3 wt. %, at most 1.2 wt. %, at most 0.8 wt. %, at most 0.6 wt. %, or in the range of 0.1 wt. % to 1.2 wt. %, 0.2 wt. % to 0.8 wt. %, or 0.2 wt. % to 0.6 wt. %, based on the total weight of the corresponding intermediate layer of the pre-sintered multi-layer dental mill blank, the weight amount being suitable for obtaining a sintering inhibitor as type II yttrium oxide in the corresponding intermediate layer of the pre-sintered multi-layer dental mill blank produced by the method.

[0680] The intermediate powder layer of the mixture of powders P2 / P3 of the green body may contain a sintering inhibitor precursor as a yttrium salt in an amount of at least 0.02 wt.-%, at least 0.05 wt.-%, at most 0.5 wt.-%, at most 0.2 wt.-%, or in the range of 0.02 wt.-% to 0.5 wt.-%, or in the range of 0.05 wt.-% to 0.2 wt.-%, based on the total weight of the corresponding intermediate layer of the pre-sintered multilayer dental mill blank, the weight amount being suitable for obtaining a sintering inhibitor as type II yttrium oxide in the corresponding intermediate layer of the pre-sintered multilayer dental mill blank produced by the method.

[0681] The method may include not adding yttrium salt as a sintering inhibitor precursor to powder P3. Thus, the top powder layer may be substantially free of yttrium salt as a sintering inhibitor precursor.

[0682] The method may include adding a specific combination of a sintering activator precursor and a sintering inhibitor precursor to powders P1 to P3 or a mixture thereof. In one embodiment, the method includes adding a sintering activator precursor (e.g., a zinc salt, a gallium salt, or a combination thereof) to powders P1 to P3 or a mixture thereof, and adding a sintering inhibitor precursor (e.g., a yttrium salt) to powder P1 or a mixture thereof. In one embodiment, the method includes adding a sintering activator precursor (e.g., a zinc salt, a gallium salt, or a combination thereof) to powders P1 to P3 or a mixture thereof, and adding a sintering inhibitor precursor (e.g., a yttrium salt) to powders P1 and P2 or a mixture thereof.

[0683] The method may include adding a coloring additive to powders P1 to P3 or a mixture thereof. The coloring additive may be added in the form of an aqueous solution. Suitable coloring additives may be, but are not limited to, multivalent ions of 3d elements and / or 4f elements of different valence states, such as, for example, Fe 3+ 、Mn 2+ 、Pr 3+ 、Tb 3+ Cr 3+ and Er 3+ , such as salts of those compounds. In one embodiment, the coloring additive comprises an erbium compound and an iron compound.

[0684] The green body may include a binder. The binder may be an organic binder or an inorganic binder. The binder may be an inorganic binder, such as water or residual moisture. The method may include debinding the green body. Debinding may be performed separately or in conjunction with pre-sintering, and is typically performed in conjunction with pre-sintering.

[0685] The preparation of the green body may include layering the powder layers in a mold. The preparation of the green body may include compacting the powder layers. Thus, the green body may be a compacted green body. Compaction may be pressing, such as, but not limited to, uniaxial pressing. Compaction may be performed at a pressure in the range of 200 MPa to 400 MPa, such as in the range of 250 MPa to 350 MPa.

[0686] One or more powder layers (optionally all powder layers) of the powder layers of the green body can be substantially planar. Each powder layer in the powder layers can have a substantially constant height. The powder layers of the green body can be arranged so that the boundaries of the powder layers are substantially parallel to each other. In one embodiment, the powder layers are substantially planar and are arranged so that the boundaries of the layers are substantially parallel to each other.

[0687] The pre-sintering of the green body has a maximum temperature of at least 700° C., at least 750° C., at least 800° C., at least 825° C., at most 1100° C., at most 1000° C., at most 950° C., at most 900° C., or in the range of 700° C. to 1100° C., in the range of 750° C. to 1000° C., in the range of 800° C. to 950° C., or in the range of 825° C. to 900° C. The maximum temperature of the pre-sintering can be maintained for a certain time, such as in the range of 1 hour to 5 hours, such as in the range of 2 hours to 3 hours.

[0688] Pre-sintering can be a pre-sintering method having a total duration in the range of 50 hours to 70 hours, such as in the range of 55 hours to 65 hours. The pre-sintering method can include one or more heating steps with a heating rate in the range of 0.05 K / min to 2 K / min or 0.1 K / min to 1.5 K / min. The pre-sintering method typically includes more than one heating step, such as more than three or more than four heating steps, which have different heating rates in the range of 0.05 K / min to 2 K / min or in the range of 0.1 K / min to 1.5 K / min. The pre-sintering method can include a heating step with a heating rate in the range of 0.05 K / min to 0.2 K / min or 0.10 K / min to 0.15 K / min in the temperature range in which debinding of the green body occurs. For example, a suitable pre-sintering method for pre-sintering the green body can be, but is not limited to, the pre-sintering method as described in Table V herein.

[0689] Table V:

[0690]

[0691] The method may include one or more additional steps common in the art. Additional steps may include, but are not limited to, mixing the powders in a mixing apparatus, adjusting the particle size distribution of the powders (e.g., by sieving), preparing the surface of the green body and / or pre-sintered dental mill blank (e.g., by grinding or polishing).

[0692] The method may be a method for preparing a pre-sintered multi-layer dental mill blank according to any one of the embodiments of the present invention.

[0693] III. Method for producing a dental restoration and the dental restoration itself

[0694] One aspect of the present invention provides a method for preparing a dental restoration, the method comprising the following steps:

[0695] - machining a pre-sintered multilayer dental mill blank according to any of the embodiments of the present invention to provide a dental restoration precursor;

[0696] - optionally surface treating the dental restoration precursor;

[0697] - sintering the dental restoration precursor to provide a dental restoration.

[0698] The machining of the pre-sintered multi-layer dental mill blank can be performed by any conventional method for machining dental mill blanks, such as by CAD / CAM methods. Machining can include, but is not limited to, cutting, drilling, and grinding the dental mill blank. The dental restoration precursor can be open porous.

[0699] Sintering is not particularly limited and can be carried out by sintering methods known in the art for sintering dental restoration precursors, and in particular for sintering zirconia ceramic dental restoration precursors. Sintering is usually complete sintering to provide a completely sintered dental restoration. Sintering can be carried out in the range of 1300°C to 1650°C, such as at a maximum sintering temperature in the range of 1400°C to 1600°C. The maximum sintering temperature can be maintained for 2 minutes to 2 hours. The total duration of sintering can be less than 45 minutes, such as in the range of 10 minutes to 45 minutes or 10 minutes to 30 minutes. Sintering can be a sintering method with a total duration of a fast sintering method as defined herein. Although short sintering is generally preferred to save time in preparing the dental restoration, it is also possible to sinter for a longer time, such as more than 45 minutes, such as in the range of 1 hour to 10 hours or 2 hours to 8 hours.

[0700] In one embodiment, the sintering is a sintering method according to any of the embodiments of the present invention, for example, as described in the following sections.

[0701] The method may include other steps known in the art, such as, but not limited to, surface treating the dental restoration precursor (e.g., by polishing) or surface treating the dental restoration (e.g., applying a stain, glaze, or veneer). In one embodiment, the method includes the step of surface treating the dental restoration precursor, such as manually surface treating the dental restoration precursor (e.g., manually surface polishing using a rotating dental polishing tool).

[0702] In one embodiment, the method comprises the following steps:

[0703] - machining a pre-sintered multilayer dental mill blank according to any of the embodiments of the present invention to provide a dental restoration precursor;

[0704] - Surface preparation of dental restoration precursors (e.g. manual surfacing);

[0705] - Sintering the surface treated dental restoration precursor to provide a dental restoration.

[0706] Another aspect of the present invention provides a dental restoration obtainable by the method for producing a dental restoration according to any one of the embodiments of the present invention.

[0707] The dental restoration may comprise a plurality of regions, such as two or more or three or more different regions. A region may have a composition different from one or more in other regions and / or one or more different properties (e.g., physical / mechanical properties, optical properties or a combination thereof). These regions may correspond to one or more layers of a pre-sintered multilayer dental grinding blank, and the dental restoration is made of these pre-sintered multilayer dental grinding blanks. The dental restoration may comprise an incision zone, a transition zone and a dentin zone. The transition zone may be arranged between the incision zone and the dentin zone and / or the incision zone is adjacent to the transition zone, and the transition zone is adjacent to the dentin zone. The incision zone may be made at least in part by the top layer of a pre-sintered multilayer dental grinding blank. The transition zone may be made at least in part by at least one intermediate layer of a pre-sintered multilayer dental grinding blank. The dentin zone may be made at least in part by the bottom layer of a pre-sintered multilayer dental grinding blank.

[0708] The dental restoration may have a desired color. At least one dental restoration or area of ​​the dental restoration may have a color that matches the VITA Classic A1–D4® color guide and a VITA bleached shade manufactured by Vita Zahnfabrik. The shade may be, but is not limited to, A1, A2, A3.5, A4, B1, B2, B3, B4, C1, C2, C3, C4, D1, D2, D3, D4, BL1, or BL2. The shade may also be a tooth shade, such as a light tooth shade, that is not part of the VITA Classic A1–D4® color guide and a VITA bleached shade manufactured by Vita Zahnfabrik. The shade may be an experimental light shade.

[0709] A dental restoration can be, but is not limited to, a crown, a partial crown, an abutment, an abutment crown, an inlay, an onlay, a veneer, a shell or a multi-unit framework, or a bridge (e.g., a 2-unit bridge, a 3-unit bridge or a 4-unit bridge), an implant bridge, etc.

[0710] IV. Sintering Method

[0711] Another aspect of the present invention provides a method for sintering a dental restoration precursor, said method having a total duration of less than 25 minutes and a maximum sintering temperature in the range of 1350° C. to 1650° C.

[0712] The method comprises subjecting the dental restoration precursor to

[0713] (i) heat treatment, and

[0714] (ii) cooling treatment,

[0715] The cooling process comprises a cooling step A,

[0716] The cooling step A starts and ends in a temperature range between 1100° C. and the maximum sintering temperature and has a cooling rate A of at least 75 K / min.

[0717] It has been found that the method for sintering a dental restoration precursor according to one embodiment of the present invention (also referred to as "sintering method" in this section) is suitable for producing a dental restoration having desired properties, and in particular desired optical properties (e.g. desired translucency), in a short time.

[0718] The method may consist of subjecting the dental restoration precursor to a heating treatment and a cooling treatment.

[0719] The method may have a total duration of less than 20 minutes, less than 18 minutes, less than 16 minutes, or less than 15 minutes. The method may have a total duration of at least 5 minutes, 8 minutes, 10 minutes, or 12 minutes. The method may have a total duration in the range of 5 minutes to less than 20 minutes, 8 minutes to less than 18 minutes, 10 minutes to less than 16 minutes, or 12 minutes to less than 15 minutes. "Total duration" is to be understood as defined in the "Definitions" section. The method may have a maximum sintering temperature in the range of 1400°C to 1600°C, in the range of 1400°C to 1560°C, in the range of 1400°C to 1500°C, or in the range of 1425°C to 1475°C. For example, the method may have a maximum sintering temperature of approximately 1450°C. The total duration described above allows for convenient production of dental restorations and is particularly believed to enable chair-side production, whereby the restoration can be provided to the patient in a single visit.

[0720] The sintering method includes a cooling process. The cooling process starts from the maximum sintering temperature and ends at a final temperature lower than the maximum sintering temperature. The cooling process includes one or more cooling steps, and typically includes more than one cooling step (e.g., two or three cooling steps). The cooling process may be followed by cooling as defined herein. Cooling is not part of the cooling process or the sintering method.

[0721] The cooling process includes a cooling step A. The cooling step A has a cooling rate of at least 75 K / min. The cooling rate determines the temperature drop (K) per minute (min). The cooling rate A can be at least 100 K / min, at least 110 K / min, at least 120 K / min, at most 250 K / min, at most 200 K / min, at most 160 K / min, in the range of 100 K / min to 250 K / min, in the range of 110 K / min to 180 K / min, or in the range of 120 K / min to 160 K / min (e.g., in the range of 125 K / min to 140 K / min). For example, the cooling rate A can be about 130 K / min.

[0722] Cooling step A begins and ends within a temperature range between 1100°C and the maximum sintering temperature. This means that cooling step A has a start temperature and an end temperature within the temperature range between 1100°C and the maximum sintering temperature. Cooling step A may begin and end within a temperature range between 1200°C and the maximum sintering temperature, or within a temperature range between 1250°C and the maximum sintering temperature, or within a temperature range between 1300°C and the maximum sintering temperature, or within a temperature range between 1325°C and the maximum sintering temperature. In one embodiment, cooling step A begins and ends within a temperature range between 1200°C and the maximum sintering temperature and has a cooling rate A of at least 100 K / min. Cooling step A may be performed for at least 20 seconds, at least 30 seconds, at least 40 seconds, at most 3 minutes, at most 2 minutes, or at most 1 minute 30 seconds, such as for a time period ranging from 20 seconds to 3 minutes, from 30 seconds to 2 minutes, or from 40 seconds to 1 minute 30 seconds.

[0723] Cooling step A may be the first cooling step of the cooling process. Thus, cooling step A may have a starting temperature that is the highest sintering temperature. For example, cooling step A may have a starting temperature of 1450°C and an ending temperature of 1350°C.

[0724] The cooling treatment may include a cooling step B, which is carried out before or after the cooling step A, and is generally carried out after the cooling step A and has a cooling rate B that is lower than the cooling rate A. It has been found that when the sintering method includes a cooling step B as described herein (optionally in addition to a cooling step C as defined herein), a dental restoration having favorable optical properties can be obtained. For example, when sintering a pre-colored dental restoration precursor to obtain more favorable color properties, and in particular when sintering a pre-colored dental restoration containing iron oxide as a main component or one of the main components of a coloring oxide, the cooling step B may be advantageous.

[0725] The cooling rate B may be at least 30 K / min, at least 50 K / min, at least 60 K / min, at most 110 K / min, at most 90 K / min, at most 80 K / min, in a range of 30 K / min to 110 K / min, in a range of 50 K / min to 90 K / min, or in a range of 60 K / min to 80 K / min.

[0726] Cooling step B can begin and end within a temperature range between 1000°C and the end temperature of cooling step A. This means that cooling step B can have a start temperature and an end temperature, both of which are within the temperature range between 1000°C and the end temperature of cooling step A. Typically, cooling step B is performed within a temperature range between 1100°C and the end temperature of cooling step A, or within a temperature range between 1150°C and the end temperature of cooling step A, or within a temperature range between 1200°C and the end temperature of cooling step A. For example, cooling step B can have a start temperature of 1350°C and an end temperature of 1200°C. Cooling step B can be performed for at least 45 seconds, at least 1 minute, at least 1 minute 30 seconds, at most 6 minutes, at most 4 minutes, or at most 3 minutes, such as for a time period ranging from 45 seconds to 6 minutes, from 1 minute to 4 minutes, or from 1 minute 30 seconds to 3 minutes.

[0727] Cooling step B may be carried out directly after cooling step A, i.e. the starting temperature of cooling step B may be the ending temperature of cooling step A. However, there may also be an intermediate cooling step between cooling step B and cooling step A, such as but not limited to cooling step C as defined herein.

[0728] Thus, the cooling process may include a cooling step C. Cooling step C may be performed after cooling step A and / or cooling step B. Cooling step C may begin and end within a temperature range between the final temperature of the cooling process (e.g., 1000° C., 1100° C., or 1150° C.) and the end temperature of cooling step A (e.g., 1200° C., 1250° C., or 1300° C.). Cooling step C may have a cooling rate C of at most 20 K / min, at most 10 K / min, at most 5 K / min, or about 0 K / min. Thus, cooling step C may be a holding step (i.e., a step in which the temperature is kept substantially constant). Cooling step C may be performed for a period of at least 45 seconds, at least 1 minute, at least 1 minute 30 seconds, at most 5 minutes, at most 4 minutes, or at most 3 minutes, such as for a period of time ranging from 45 seconds to 5 minutes, from 1 minute to 4 minutes, or from 1 minute 30 seconds to 3 minutes. Performing the cooling step C may be advantageous when the dental restoration precursor is a pre-colored dental restoration, eg comprising two or more units, such as but not limited to a dental bridge.

[0729] The cooling process may comprise one or more additional cooling steps (including a holding step) performed before or after any one of cooling steps A to C as defined herein. In one embodiment, the cooling process comprises cooling step A and cooling step B, optionally in combination with cooling step C.

[0730] The final temperature of the cooling process can be at least 1000°C, at least 1100°C, at least 1150°C, at most 1300°C, at most 1280°C, or at most 1250°C, such as within the range of 1000°C to 1300°C, within the range of 1100°C to 1280°C, or within the range of 1150°C to 1250°C. For example, the final temperature of the cooling process can be 1200°C. The cooling process can be carried out for a period of at least 1 minute, at least 2 minutes, at least 2 minutes and 30 seconds, at most 8 minutes, at most 6 minutes, or at most 4 minutes, such as within the range of 1 minute to 8 minutes, 2 minutes to 6 minutes, or 2 minutes and 30 seconds to 4 minutes. The cooling process is typically followed by cooling. Cooling can be carried out at least partially with the sintering furnace open. Cooling can be considered to be completed at a temperature of about 400°C. Cooling may require less than 10 minutes, such as less than 5 minutes, such as less than 3 minutes.

[0731] The sintering method includes a heating process. The heating process starts at a starting temperature and ends at a maximum sintering temperature. The starting temperature of the heating process can be a temperature in the range of 5°C to 30°C, for example 25°C.

[0732] The heat treatment comprises one or more heating steps until the maximum sintering temperature is reached. The heat treatment typically comprises a heating step A having a heating rate A of at least 150 K / min, at least 170 K / min, at least 190 K / min, at most 300 K / min, at most 250 K / min or at most 220 K / min, such as in the range of 150 K / min to 300 K / min, in the range of 170 K / min to 250 K / min or in the range of 190 K / min to 220 K / min. The heating rate determines the temperature increase (K) per minute (min). For example, the heating rate A can be 200 K / min. The heating step A can start and end in a temperature range between the starting temperature of the heat treatment (e.g., 25° C.) and the maximum sintering temperature. The heating step A can start and end in a temperature range between the starting temperature of the heat treatment and a temperature lower than the maximum sintering temperature. Heating step A may start and end within a temperature range between the start temperature of the heat treatment and a temperature of 1300° C., or within a temperature range between the start temperature and a temperature of 1200° C., or within a temperature range between the start temperature and a temperature of 1100° C. For example, heating step A may start at 25° C. and end at 1050° C. Heating step A may be performed for a period of at least 3 minutes, at least 4 minutes, at most 7 minutes, at most 6 minutes, such as within a range of 3 to 7 minutes or 4 to 6 minutes.

[0733] Heat treatment can comprise two or more heating steps.Heat treatment can comprise heating step B after heating step A, and heating step B has heating rate B lower than heating rate A.Heat rate B can be at least 50 K / min, at least 70 K / min, at least 90 K / min, at most 200 K / min, at most 150 K / min, at most 120 K / min, in the range of 50 K / min to 200 K / min, in the range of 70 K / min to 150 K / min or in the range of 90 K / min to 120 K / min.For example, heating rate B can be 100 K / min.In one embodiment, heat treatment comprises heating step A with heating rate A of at least 170 K / min, and heating step B after heating step A, and heating step B has heating rate B of at least 70 K / min and is lower than heating rate A.

[0734] Heating step B can begin and end within a temperature range between the end temperature of heating step A and the maximum sintering temperature. Heating step B can begin directly after heating step A, i.e., the start temperature of heating step B can be the end temperature of heating step A. Heating step B can end at the maximum sintering temperature. For example, heating step B can begin at a temperature of 1050°C and end at a maximum sintering temperature of 1450°C. Heating step B can be performed for at least 1 minute, at least 2 minutes, at least 3 minutes, at most 7 minutes, at most 6 minutes, or at most 5 minutes, such as for a period of time ranging from 1 minute to 7 minutes, from 2 minutes to 6 minutes, or from 3 minutes to 5 minutes.

[0735] In addition, heat treatment can include a heating step C after heating step B, and heating step C has a heating rate C lower than heating rate B. Heating step C can have a heating rate C of at most 40 K / min, at most 20 K / min, at most 10 K / min. Heating step C can end at the highest sintering temperature. Usually, heating step C is carried out at the highest sintering temperature and has a heating rate C of about 0 K / min. Therefore, heating step C is normally a holding step (that is, a step in which the temperature is kept substantially constant) at the highest sintering temperature. The highest sintering temperature can be kept for at least 30 seconds, at least 1 minute, at most 5 minutes, at most 3 minutes, in the range of 30 seconds to 5 minutes or in the range of 1 minute to 3 minutes. For example, the highest sintering temperature can be kept for about 2 minutes. When heat treatment ends, the dental restoration precursor is usually completely sintered.

[0736] The heat treatment may include one or more additional heating steps (including a holding step) performed before or after any one of heating step A and heating step B as defined herein. The heat treatment may also include one or more additional controlled heating steps (including a holding step) performed before or after heating step C. When heating step C is a holding step at the maximum sintering temperature, there is no additional heating step after heating step C. In one embodiment, the heat treatment consists of heating step A to heating step C. The heat treatment may be performed for at least 5 minutes, at least 7 minutes, at least 8 minutes, at most 16 minutes, at most 14 minutes, or at most 12 minutes, such as a time period in the range of 5 minutes to 16 minutes, 7 minutes to 14 minutes, or 8 minutes to 12 minutes.

[0737] The heat treatment can be carried out at least partially at a lower pressure than that applied during other parts of the sintering process, such as during the cooling process. The lower pressure can be 500 mbar or less, 200 mbar or less, 150 mbar or less, or 100 mbar or less, such as a pressure in the range of 0.1 mbar to 500 mbar, 1 mbar to 200 mbar, 10 mbar to 150 mbar, or 50 mbar to 100 mbar. The pressure can be adjusted by applying a vacuum. The vacuum can be applied before starting the heat treatment or during the heat treatment, such as in a temperature range of 25°C to 500°C or 25°C to 100°C. When the heat treatment is carried out at least partially at a lower pressure as described herein, the properties of the dental restoration, such as density or contrast, can be further optimized.

[0738] The heat treatment may be carried out partially at a lower pressure. A lower pressure may be applied in a temperature range between the starting temperature and a temperature lower than the maximum sintering temperature. For example, a lower pressure may be applied in a temperature range between the starting temperature and a temperature 50°C lower than the maximum sintering temperature. The heat treatment may comprise a heating step A and a heating step B as defined herein, wherein heating step A is partially or completely, optionally completely, carried out at a lower pressure, and heating step B is partially carried out at a lower pressure. When a portion of the heat treatment is carried out at a lower pressure, the remainder of the sintering process may be carried out at a pressure higher than 900 mbar, such as ambient pressure. The heat treatment, and in particular the portion of the heat treatment that is not carried out at a lower pressure, may be carried out under a gas flow, such as air, oxygen-enriched air or oxygen. The gas flow may have a flow rate in the range of 0.1 l / min to 50 l / min, such as in the range of 1 l / min to 10 l / min, such as in the range of 2 l / min to 5 l / min.

[0739] The dental restoration precursor can be a porous ceramic material, particularly an open porous ceramic material. The dental restoration precursor can have a density of at least 45%, at least 50%, at least 52%, at most 70%, at most 60%, at most 55% relative to its theoretical density, such as in the range of 45% to 70% (e.g., 45% to 55%), 50% to 60% or 52% to 55% (e.g., approximately 52% or approximately 53%). In one embodiment, the density of the pre-sintered multilayer dental mill blank is in the range of 45% to 55% relative to its theoretical density. The dental restoration precursor can be a pre-sintered ceramic material. Therefore, the dental restoration precursor can be a ceramic material that has been pre-sintered before being subjected to a sintering method. For example, the dental restoration precursor may be a ceramic material having a maximum pre-sintering temperature of at least 700°C, at least 750°C, at least 800°C, at least 825°C, at most 1100°C, at most 1000°C, at most 950°C, at most 900°C, such as in the range of 700°C to 1100°C, in the range of 750°C to 1000°C, in the range of 800°C to 950°C, or in the range of 825°C to 900°C.

[0740] The dental restoration precursor can be, but is not limited to, a crown, a partial crown, an abutment, an abutment crown, an inlay, an onlay, a veneer, a shell or a multi-unit framework, or a precursor to a bridge (e.g., a 2-unit bridge, a 3-unit bridge or a 4-unit bridge), an implant bridge, etc.

[0741] The dental restoration precursor may be pre-colored, for example, the dental restoration precursor may include a colored metal oxide. Suitable colored metal oxides may be, but are not limited to, oxides of Fe, Mn, Cr, Pr, Tb, Er, Yb, Ce, Co, Ni, Nd, Cu, Bi, and any combination thereof. The colored oxide may comprise iron oxide, typically in combination with other colored metal oxides. It has been found that the sintering method according to an embodiment of the present invention is particularly suitable for preparing dental restorations comprising colored metal oxides, and in particular iron oxide, in a very short time.

[0742] The dental restoration precursor can be a zirconia dental restoration, i.e. it can be based on zirconia as the main component. The dental restoration precursor can contain zirconia and yttrium oxide. The dental restoration precursor can contain different cross-sections, such as at least 3 cross-sections, containing zirconia and yttrium oxide, and each cross-section has a different yttrium oxide content. The different cross-sections can be a top cross-section (e.g., at least partially forming the incision area of ​​the dental restoration), at least one intermediate cross-section (e.g., at least partially forming the transition area of ​​the dental restoration) and a bottom cross-section (e.g., at least partially forming the dentin area of ​​the dental restoration). The yttrium oxide content can increase from the bottom cross-section to the intermediate cross-section and then to the top cross-section. The sintering method is suitable for sintering multi-section dental restoration precursors and / or dental restoration precursors obtained from multi-layer dental mill blanks, and therefore a dental restoration with a desired optical appearance can be provided in a short period of time.

[0743] The dental restoration precursor can be prepared from a multilayer dental mill blank, such as a pre-sintered multilayer dental mill blank. The multilayer dental mill blank (such as a pre-sintered multilayer dental mill blank) can be pre-colored. The multilayer dental mill blank (such as a pre-sintered multilayer dental mill blank) can include a top layer, a bottom layer, and at least one intermediate layer, each layer comprising zirconium oxide and yttrium oxide, and the yttrium oxide content of the layers can increase from the bottom layer to the top layer.

[0744] A dental restoration precursor can be prepared from the pre-sintered multi-layer dental mill blank according to any one of the embodiments of the present invention. When a dental restoration precursor is prepared from the pre-sintered multi-layer dental mill blank according to one of the embodiments of the present invention, a dental restoration having a natural and highly aesthetic appearance can be obtained in a very short time.

[0745] Another aspect of the present disclosure relates to a dental oven. The dental oven is configured to carry out the method for sintering a dental restoration precursor according to any of the embodiments described herein. The dental oven typically comprises a sintering chamber, a heating device, and a control unit, and optionally comprises or is connected to a vacuum device. The dental oven is capable of sintering the dental restoration precursor according to the sintering method as described herein. In particular, the heating device is capable of achieving a maximum sintering temperature of up to 1600°C, such as up to 1560°C. The heating device is capable of achieving a heating rate of up to 300 K / min, such as up to 250 K / min. The dental oven furnace can be configured to achieve a cooling rate of up to 180 K / min, such as up to 150 K / min. The vacuum device is capable of achieving a vacuum in the sintering chamber of less than 500 mbar, such as less than 150 mbar or in the range of 40 mbar to 120 mbar. Dental ovens per se (i.e., in a form not specifically configured to carry out the sintering method of the present invention) are known in the art. A suitable dental oven is for example the Programat CS6 commercially available from Ivoclar Vivadent AG.

[0746] The control unit is connected to the equipment of the dental oven (such as the equipment described herein). The control unit includes a device suitable for causing the dental oven to perform the sintering method according to the embodiments described herein. In particular, the control unit includes a device suitable for causing the dental oven to perform a heating process, a cooling process, and optionally a pressure regulation, as described herein. Therefore, the control unit may include a data processing device (computer) that is configured to cause the dental oven to perform the sintering method. More specifically, the data processing device may have a storage unit and a computing unit. The storage unit may contain a computer-readable medium storing a computer program. The computer program and therefore the computer-readable medium may contain commands that, when executed by the computing unit, or more generally, by the computer, cause the computing unit or computer to communicate with the equipment of the dental oven to perform the required processing steps (e.g., heating process, cooling process, pressure regulation, and chamber opening / closing). In other words, a series of steps of the sintering method (e.g., the order of steps as described in Table 5 herein) can be programmed on the data processing device (computer) of the dental oven. Therefore, the dental restoration precursor (placed in the sintering chamber) can be sintered using the sintering method according to the present disclosure.

[0747] Therefore, another aspect of the present disclosure relates to a computer program comprising or storing commands that, when a computer executes the computer program, cause the computer to perform a sintering method according to any one of the embodiments described herein. Yet another aspect of the present disclosure relates to a computer-readable medium storing or comprising commands that, when executed by a computer, cause the computer to perform a sintering method according to any one of the embodiments described herein. In particular, the computer is coupled or communicated with a dental oven (such as the dental oven described above) so that a dental restoration precursor can be sintered using the sintering method as described herein. In another aspect of the present disclosure, a data processing device is provided, comprising a device for performing a sintering method according to any one of the embodiments described herein. In particular, the data processing device is coupled or communicated with a dental oven (such as the dental oven described above) so that a dental restoration precursor can be sintered using the sintering method as described herein. The data processing device can be part of a control unit of a dental oven as described above.

[0748] V. Non-Limiting Aspects and Embodiments of the Invention

[0749] Other non-limiting embodiments of the present invention are defined in the following numbered items [1] to

[174] and [1b] to [29b]:

[0750] [1] A pre-sintered multi-layer dental grinding blank comprising

[0751] Top floor,

[0752] bottom layer, and

[0753] At least one intermediate layer,

[0754] The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer,

[0755] When fully sintered by the flash sintering method, the representative test cross section has increasing contrast from the top layer to the bottom layer.

[0756] [2] The pre-sintered multi-layer dental mill blank according to item [1], wherein the contrast gradually increases from the top layer to the bottom layer, so that the contrast of the top layer is lower than the contrast of the at least one middle layer, and the contrast of the at least one middle layer is lower than the contrast of the bottom layer.

[0757] [3] The pre-sintered multi-layer dental mill blank according to item [1] or [2], wherein the contrast increases layer by layer from the top layer to the bottom layer.

[0758] [4] The pre-sintered multi-layer dental mill blank according to any one of items [1] to [3], wherein the contrast [%] of each layer is at least 56%, at least 61%, at least 62% or at least 64%, and / or the contrast [%] of each layer is at most 88%, at most 83%, at most 82% or at most 79%.

[0759] [5] The pre-sintered multi-layer dental mill blank according to any one of items [1] to [4], wherein the contrast [%] of each layer is in the range of 56% to 88%, 61% to 83%, 62% to 82% or 64% to 79%.

[0760] [6] A pre-sintered multi-layer dental mill blank according to any one of items [1] to [5], wherein the contrast [%] of the bottom layer differs from the contrast [%] of the top layer by at least 2 percentage points, at least 3 percentage points, at least 5 percentage points, at least 8 percentage points or at least 10 percentage points, and / or the contrast [%] of the bottom layer differs from the contrast [%] of the top layer by at most 24 percentage points, at most 22 percentage points, at most 19 percentage points, at most 18 percentage points or at most 16 percentage points.

[0761] [7] A pre-sintered multi-layer dental mill blank according to any one of items [1] to [6], wherein the contrast [%] of the bottom layer differs from the contrast [%] of the top layer by 2 percentage points to 24 percentage points, 3 percentage points to 22 percentage points, 5 percentage points to 19 percentage points, 8 percentage points to 18 percentage points or 10 percentage points to 16 percentage points.

[0762] [8] The pre-sintered multi-layer dental mill blank according to any one of items [1] to [7], wherein the contrast of the bottom layer is at least 66%, at least 70%, at least 71% or at least 74%, and / or the contrast of the bottom layer is at most 88%, at most 83%, at most 81% or at most 80%.

[0763] [9] A pre-sintered multi-layer dental mill blank according to any one of items [1] to [8], wherein the contrast of the bottom layer is in the range of 66% to 88%, 70% to 83%, 71% to 81% or 74% to 80%.

[0764]

[10] The pre-sintered multi-layer dental mill blank according to any one of items [1] to [9], wherein the contrast of the top layer is at least 56%, at least 61%, at least 62% or at least 64%, and / or the contrast of the top layer is at most 72%, at most 68%, at most 67% or at most 66%.

[0765]

[11] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[10] , wherein the contrast of the top layer is in the range of 56% to 72%, 61% to 68%, 62% to 67% or 64% to 66%.

[0766]

[12] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[11] , wherein the contrast of the at least one intermediate layer is at least 62%, at least 66%, at least 67% or at least 68%, and / or the contrast of the at least one intermediate layer is at most 83%, at most 79%, at most 78% or at most 76%.

[0767]

[13] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[12] , wherein the contrast of the at least one intermediate layer is in the range of 62% to 83%, 66% to 79%, 67% to 78% or 68% to 76%.

[0768]

[14] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[13] , wherein the contrast [%] of each pair of two adjacent layers differs by at least 0.3 percentage points, at least 0.5 percentage points, at least 1.0 percentage points or at least 2.0 percentage points.

[0769]

[15] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[14] , comprising at least two intermediate layers, the contrast [%] of one intermediate layer differing from the contrast of the other intermediate layer by at least 0.2 percentage points, at least 0.5 percentage points, at least 3.0 percentage points or at least 4.0 percentage points, and / or at most 12 percentage points, at most 10.0 percentage points, at most 9.0 percentage points or at most 8.0 percentage points.

[0770]

[16] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[15] , comprising or consisting of the following layers:

[0771] Top floor L4,

[0772] Middle layer L3,

[0773] Middle layer L2,

[0774] The bottom layer L1, and

[0775] The contrast of the layer satisfies one or more of the contrast profiles A1.1 to J1.1 as defined in Table A1 herein (optionally, one or more of the contrast profiles C1.1 to H1.1) or the contrast profiles A1.2 to J1.2 as defined in Table A2 herein (optionally, one or more of the contrast profiles C1.2 to H1.2).

[0776]

[17] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[16] , wherein when fully sintered by a rapid sintering method, the representative test section has a CIE brightness L* that increases layer by layer from the bottom layer to the top layer.

[0777]

[18] A pre-sintered multi-layer dental mill blank comprising

[0778] Top floor,

[0779] bottom layer, and

[0780] At least one intermediate layer,

[0781] The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer,

[0782] When fully sintered by the flash sintering method, the representative test cross-section has a CIE lightness L* that increases from the bottom layer to the top layer.

[0783]

[19] The pre-sintered multi-layer dental mill blank according to item

[18] , wherein the CIE brightness L* increases from the bottom layer to the top layer, so that the CIE brightness L* of the bottom layer is lower than the CIE brightness L* of the at least one intermediate layer, and the CIE brightness L* of the at least one intermediate layer is lower than the CIE brightness L* of the bottom layer.

[0784]

[20] The pre-sintered multi-layer dental mill blank according to any one of items

[18] to

[19] , wherein the CIE brightness L* increases layer by layer from the top layer to the bottom layer.

[0785]

[21] The pre-sintered multilayer dental mill blank according to any one of items

[18] to

[20] , wherein the CIE brightness L* of each layer is at least 72, at least 76, at least 78 or at least 79, and / or the CIE brightness L* of each layer is at most 98, at most 94, at most 92 or at most 91.

[0786]

[22] A pre-sintered multilayer dental mill blank according to any one of items

[18] to

[21] , wherein the CIE brightness L* of each layer is in the range of 72 to 98, 76 to 94, 78 to 92 or 79 to 91.

[0787]

[23] The pre-sintered multilayer dental mill blank according to any one of items

[18] to

[22] , wherein the CIE brightness L* of each pair of two adjacent layers differs by at least 0.05, at least 0.4, at least 0.6 or at least 0.8.

[0788]

[24] The pre-sintered multi-layer dental mill blank according to any one of items

[18] to

[23] , wherein the CIE brightness L* of the bottom layer may be at least 72, at least 76, at least 78, at least 80, at least 82 or at least 84, and / or the CIE brightness L* of the bottom layer may be at most 94, at most 92, at most 90, at most 88, at most 86 or at most 84.

[0789]

[25] A pre-sintered multi-layer dental mill blank according to any one of items

[18] to

[26] , wherein the CIE brightness L* of the bottom layer is in the range of 72 to 94, 76 to 92, 78 to 90, 80 to 88 or 80 to 86.

[0790]

[26] The pre-sintered multi-layer dental mill blank according to any one of items

[18] to

[25] , wherein the CIE brightness L* of the top layer is at least 80, at least 84, at least 86, at least 88 or at least 90, and / or the CIE brightness L* of the top layer is at most 98, at most 96, at most 94, at most 92 or at most 90.

[0791]

[27] A pre-sintered multi-layer dental mill blank according to any one of items

[18] to

[26] , wherein the CIE brightness L* of the top layer is in the range of 80 to 98, 84 to 94, 86 to 92 or 86 to 90.

[0792]

[28] The pre-sintered multi-layer dental mill blank according to any one of items

[18] to

[27] , wherein the CIE brightness L* of the top layer is at least 0.5, at least 1.0, at least 2.0, at least 3.0 or at least 4.0 higher than the CIE brightness L* of the bottom layer, and / or the CIE brightness L* of the top layer is at most 12, at most 10, at most 9.0, at most 8.0 or at most 7.0 higher than the CIE brightness of the bottom layer.

[0793]

[29] The pre-sintered multi-layer dental mill blank according to any one of items

[18] to

[28] , wherein the CIE brightness L* of the top layer is higher than the CIE brightness L* of the bottom layer by a value in the range of 0.5 to 12, 1.0 to 10, 2.0 to 9.0, 2.0 to 8.0 or 2.0 to 7.0.

[0794]

[30] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[29] , wherein when fully sintered by a rapid sintering method, the representative test section has a CIE a* value, and the CIE a* value of each layer is in the range of -3.5 to 7.5, -2.2 to 6.0, -1.8 to 5.6 or -1.0 to 5.0.

[0795]

[31] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[30] , wherein the representative test cross-section has a CIE a* value when fully sintered by a rapid sintering method, the CIE a* value of each layer being at least -3.5, at least -2.2, at least -1.8 or at least -1.0, and / or the CIE a* value of each layer being at most 7.5, at most 6.0, at most 5.6 or at most 5.0.

[0796]

[32] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[31] , wherein when fully sintered by a rapid sintering method, the representative test section has a CIE a* value that increases layer by layer from the top layer to the bottom layer.

[0797]

[33] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[32] , wherein the representative test section has a CIE b* value when fully sintered by a rapid sintering method, and the CIE b* value of each layer is in the range of 1 to 30, 3 to 26, 4 to 24 or 11 to 22.

[0798]

[34] The pre-sintered multilayer dental mill blank according to any one of items [1] to

[33] , wherein the representative test cross-section has a CIE b* value when fully sintered by a rapid sintering method, the CIE b* value of each layer being at least 1, at least 3, at least 4 or at least 11, and / or the CIE b* value of each layer being at most 30, at most 26, at most 24 or at most 22.

[0799]

[35] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[34] , comprising or consisting of the following layers:

[0800] Top floor L4,

[0801] Middle layer L3,

[0802] Middle layer L2,

[0803] The bottom layer L1, and

[0804] When fully sintered by the fast sintering method, the representative test cross-section has a CIE brightness L*, and the CIE brightness L* of the layer satisfies one or more of the CIE brightness L* distributions A2.1 to J2.1 as defined in Table B1 herein (optionally, one or more of the CIE brightness L* distributions C2.1 to H2.1) or one or more of the CIE brightness L* distributions A2.2 to J2.2 as defined in Table B2 herein (optionally, one or more of the CIE brightness L* distributions C2.2 to H2.2).

[0805]

[36] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[35] , comprising or consisting of the following layers:

[0806] Top floor L4,

[0807] Middle layer L3,

[0808] Middle layer L2,

[0809] The bottom layer L1, and

[0810] When fully sintered by the flash sintering method, the representative test cross-section has a CIE a* value, and the CIE a* value of the layer satisfies one or more of the CIE a* value distributions A3.1 to J3.1 as defined in Table C1 herein or one or more of the CIE a* value distributions A3.2 to J3.2 as defined in Table C2 herein.

[0811]

[37] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[36] , comprising or consisting of the following layers:

[0812] Top floor L4,

[0813] Middle layer L3,

[0814] Middle layer L2,

[0815] The bottom layer L1, and

[0816] When fully sintered by the flash sintering method, the representative test cross-section has a CIE b* value, and the CIE b* value of the layer satisfies one or more of the CIE b* value distributions A4.1 to J4.1 as defined in Table D1 herein or one or more of the CIE b* value distributions A4.2 to J4.2 as defined in Table D2 herein.

[0817]

[38] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[37] , comprising or consisting of the following layers:

[0818] Top floor L4,

[0819] Middle layer L3,

[0820] Middle layer L2,

[0821] The bottom layer L1, and

[0822] When fully sintered by the flash sintering method, the representative test cross-section has a CIE L*a*b* value and contrast ratio, and the CIE L*a*b* value and contrast ratio of the layer satisfy one or more of the optical property distributions A to J as defined in Table F1 herein (optionally, one or more of the optical property distributions C to H) or one or more of the optical property distributions Aa to Jj as defined in Table F2 herein (optionally, one or more of the optical property distributions Cc to Hh).

[0823]

[39] The pre-sintered multi-layer dental milling blank according to any one of items [1] to

[38] , which is a pre-sintered multi-layer zirconia ceramic dental milling blank.

[0824]

[40] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[39] , each layer comprising zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer.

[0825]

[41] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[40] , each layer comprising zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, such that the bottom layer has a lower yttrium oxide content than the at least one intermediate layer, and the at least one intermediate layer has a lower yttrium oxide content than the top layer.

[0826]

[42] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[41] , wherein each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer.

[0827]

[43] A pre-sintered multi-layer dental mill blank comprising

[0828] Top floor,

[0829] bottom layer, and

[0830] At least one intermediate layer,

[0831] each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer,

[0832] The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer, and

[0833] Representative tested cross sections of the top layer and / or an intermediate layer adjacent to the top layer have less than 0.25, less than 0.20, less than 0.15, less than 0.10, less than 0.05, or less than 0.02 pores per grain when fully sintered by a flash sintering process.

[0834]

[44] A pre-sintered multi-layer dental mill blank according to item

[43] , wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, such that the bottom layer has a lower yttrium oxide content than the at least one intermediate layer, and the at least one intermediate layer has a lower yttrium oxide content than the top layer.

[0835]

[45] A pre-sintered multi-layer dental mill blank according to any one of items

[43] to

[44] , wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer.

[0836]

[46] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[45] , wherein a representative test cross-section of the top layer has a pore count per grain of less than 0.25, less than 0.20, less than 0.15, less than 0.10, less than 0.05 or less than 0.02 when fully sintered by a rapid sintering method.

[0837]

[47] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[46] , wherein a representative test cross-section of the intermediate layer adjacent to the top layer has a pore count per grain of less than 0.25, less than 0.20, less than 0.15, less than 0.10, less than 0.05 or less than 0.02 when fully sintered by a rapid sintering method.

[0838]

[48] ​​The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[47] , wherein a representative test section of the top layer and / or the intermediate layer adjacent to the top layer has an intra-particle pore number per particle of less than 0.20, less than 0.15, less than 0.10, less than 0.05 or less than 0.02 when fully sintered by a rapid sintering method.

[0839]

[49] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[48] , wherein the top layer comprises a sintering activator.

[0840]

[50] A pre-sintered multi-layer dental mill blank comprising

[0841] Top floor,

[0842] bottom layer, and

[0843] At least one intermediate layer,

[0844] Each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, and

[0845] The top layer comprises a sintering activator.

[0846]

[51] The pre-sintered multi-layer dental mill blank according to item

[50] , wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, such that the bottom layer has a lower yttrium oxide content than the at least one intermediate layer, and the at least one intermediate layer has a lower yttrium oxide content than the top layer.

[0847]

[52] A pre-sintered multi-layer dental mill blank according to any one of items

[51] to

[52] , wherein the yttrium oxide content of the layers increases layer by layer from the bottom layer to the top layer.

[0848]

[53] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[52] , wherein the top layer comprises aluminum oxide in an amount of less than 0.05 wt%, or less than 0.02 wt%, or less than 0.01 wt%, based on the total weight of the top layer.

[0849]

[54] A pre-sintered multi-layer dental mill blank comprising

[0850] Top floor,

[0851] bottom layer, and

[0852] At least one intermediate layer,

[0853] Each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, and

[0854] The top layer comprises aluminum oxide in an amount less than 0.01 wt %, based on the total weight of the top layer.

[0855]

[55] A pre-sintered multi-layer dental mill blank according to item

[54] , wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, such that the bottom layer has a lower yttrium oxide content than the at least one intermediate layer, and the at least one intermediate layer has a lower yttrium oxide content than the top layer.

[0856]

[56] A pre-sintered multi-layer dental mill blank according to any one of items

[55] to

[55] , wherein the yttrium oxide content of the layers increases layer by layer from the bottom layer to the top layer.

[0857]

[57] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[56] , wherein each layer comprises a sintering activator.

[0858]

[58] The pre-sintered multi-layer dental mill blank according to item

[57] , wherein the top layer comprises a higher amount of the sintering activator than the bottom layer, and

[0859] Optionally, the content of the sintering activator decreases layer by layer from the top layer to the bottom layer.

[0860]

[59] The pre-sintered multi-layer dental mill blank according to item

[57] or

[58] ,

[0861] The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer,

[0862] The weight amount of the sintering activator in each of the layers of the pre-sintered multi-layer dental mill blank is adjusted so that each of the representative test sections has a maximum sintering rate at temperature T when fully sintered by a rapid sintering method, wherein the temperature T of the representative test sections differs by no more than 40°C or by no more than 25°C.

[0863]

[60] A pre-sintered multi-layer dental mill blank according to any one of items

[49] to

[59] , wherein the top layer comprises the sintering activator in an amount of at least 0.02 wt%, at least 0.05 wt%, at least 0.10 wt% or at least 0.15 wt%, based on the total weight of the top layer, and / or the top layer comprises the sintering activator in an amount of at most 0.8 wt%, at most 0.50 wt%, at most 0.30 wt% or at most 0.20 wt%, based on the total weight of the top layer.

[0864]

[61] The pre-sintered multilayer dental mill blank according to any one of items

[49] to

[60] , wherein the top layer comprises the sintering activator in an amount ranging from 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.50 wt%, 0.10 wt% to 0.30 wt% or 0.15 wt% to 0.20 wt%, based on the total weight of the top layer.

[0865]

[62] A pre-sintered multilayer dental mill blank according to any one of items

[57] to

[61] , wherein each layer comprises the sintering activator in an amount of at least 0.02 wt%, at least 0.05 wt% or at least 0.10 wt%, based on the total weight of the corresponding layer, and / or each layer comprises the sintering activator in an amount of at most 0.8 wt%, at most 0.50 wt% or at most 0.30 wt%, based on the total weight of the corresponding layer.

[0866]

[63] A pre-sintered multilayer dental mill blank according to any one of items

[57] to

[62] , wherein each layer comprises the sintering activator in an amount ranging from 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.50 wt% or 0.10 wt% to 0.30 wt%, based on the total weight of the corresponding layer.

[0867]

[64] According to any one of items

[49] to

[63] , the sintering activator can be obtained by converting a sintering activator precursor into the sintering activator when pre-sintering the green body of the multi-layer dental milling blank.

[0868]

[65] A pre-sintered multilayer dental mill blank according to any one of items

[49] to

[63] , wherein the sintering activator is zinc oxide, gallium oxide or a combination thereof.

[0869]

[66] A pre-sintered multi-layer dental mill blank according to any one of items

[49] to

[65] , wherein the sintering activator is zinc oxide.

[0870]

[67] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[66] ,

[0871] Each layer comprises a combined amount of zirconium oxide, yttrium oxide and hafnium dioxide of at least 80 wt.-%, at least 90 wt.-%, at least 95 wt.-% or at least 98 wt.-%, based on the total weight of the respective layer of the pre-sintered multilayer dental abrasive blank, and / or each layer comprises a combined amount of zirconium oxide, aluminum oxide and zirconium dioxide of at most 99.8 wt.-%, at most 99.6 wt.-%, at most 99.4 wt.-% or at most 99.2 wt.-%, based on the total weight of the respective layer of the pre-sintered multilayer dental abrasive blank.

[0872]

[68] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[67] , wherein each layer comprises a combined amount of zirconium oxide, yttrium oxide and hafnium dioxide in the range of 80 wt % to 99.8 wt %, 90 wt % to 99.6 wt %, 95 wt % to 99.4 wt %, or 98 wt % to 99.2 wt %, based on the total weight of the corresponding layer of the pre-sintered multilayer dental mill blank.

[0873]

[69] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[68] ,

[0874] Each layer comprises zirconium oxide in an amount by weight of at least 80 wt.-%, at least 85 wt.-%, at least 87 wt.-% or at least 88 wt.-%, based on the total weight of the respective layer of the pre-sintered multilayer dental abrasive blank, and / or each layer comprises zirconium oxide in an amount by weight of at most 95 wt.-%, at most 94 wt.-%, at most 93 wt.-% or at most 92 wt.-%, based on the total weight of the respective layer of the pre-sintered multilayer dental abrasive blank.

[0875] Or each layer comprises zirconium oxide in an amount by weight ranging from 80 wt % to 95 wt %, 85 wt % to 94 wt %, 87 wt % to 93 wt %, 88 wt % to 92 wt %, based on the total weight of the corresponding layer of the pre-sintered multilayer dental mill blank.

[0876]

[70] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[69] , wherein each layer comprises hafnium dioxide in a weight ratio to zirconium oxide in the range of 0:100 to 5:95, 1:99 to 4:96, 2:98 to 3:97 or 2:98, based on the total weight of hafnium dioxide and zirconium oxide of the corresponding layer of the pre-sintered multilayer dental mill blank.

[0877]

[71] The pre-sintered multilayer dental mill blank according to any one of items [1] to

[70] , wherein the top layer comprises at least 7.0 wt.%, at least 8.0 wt.%, at least 9.0 wt.% or at least 9.5 wt.% yttrium oxide, based on the total weight of the top layer,

[0878] And / or the top layer comprises at most 13.0 wt%, at most 12.0 wt%, at most 11.0 wt% or at most 10.5 wt% yttrium oxide, based on the total weight of the top layer.

[0879]

[72] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[71] , wherein the top layer comprises yttrium oxide in an amount by weight in the range of 7.0 wt% to 13.0 wt%, 8.0 wt% to 12.0 wt% (e.g., in the range of 9.0 wt% to 12.0 wt%), 9.0 wt% to 11.0 wt% or 9.5 wt% to 10.5 wt%, based on the total weight of the top layer.

[0880]

[73] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[72] , wherein the bottom layer comprises at least 4.0 wt.%, at least 5.0 wt.%, at least 5.5 wt.% or at least 6.0 wt.% of yttrium oxide, based on the total weight of the bottom layer, and / or the bottom layer comprises at most 8.0 wt.%, at most 7.5 wt.%, at most 7.0 wt.% or at most 6.8 wt.% of yttrium oxide, based on the total weight of the bottom layer.

[0881]

[74] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[73] , wherein the bottom layer comprises 4.0 wt% to 8.0 wt%, 5.0 wt% to 7.5 wt%, 5.5 wt% to 7.0 wt% or 6.0 wt% to 6.8 wt% of yttrium oxide based on the total weight of the bottom layer.

[0882]

[75] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[74] , wherein the top layer comprises yttrium oxide in an amount by weight of at least 9.0 wt% (e.g., in the range of 9.0 wt% to 12.0 wt%), such as at least 9.5 wt%, such as in the range of 9.5 wt% to 10.5 wt%, based on the total weight of the top layer, and the bottom layer comprises yttrium oxide in an amount by weight of at most 7.5 wt%, such as at most 7.0 wt%, such as in the range of 5.5 wt% to 7.5 wt%, based on the total weight of the bottom layer.

[0883]

[76] The pre-sintered multilayer dental mill blank according to any one of items [1] to

[75] , wherein each of the at least one intermediate layer comprises 5.0 wt% to 11.0 wt%, 6.0 wt% to 10.5 wt%, 6.5 wt% to 10.0 wt% or 7.0 wt% to 9.5 wt% of yttrium oxide, based on the total weight of the corresponding layer of the at least one intermediate layer.

[0884]

[77] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[76] , wherein each of the at least one intermediate layer comprises at least 5.0 wt.%, at least 6.0 wt.%, at least 6.5 wt.% or at least 7.0 wt.%, based on the total weight of the corresponding layer of the at least one intermediate layer, and / or the at least one intermediate layer comprises at most 11.0 wt.%, at most 10.5 wt.%, at most 10.0 wt.% or 9.5 wt.%, based on the total weight of the corresponding layer of the at least one intermediate layer.

[0885]

[78] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[77] , comprising or consisting of the following layers:

[0886] Top floor L4,

[0887] Middle layer L3,

[0888] Middle layer L2,

[0889] The bottom layer L1, and

[0890] The top layer L4 contains yttrium oxide in an amount ranging from 7.0 wt% to 13.0 wt%, 8.0 wt% to 12.0 wt%, 9.0 wt% to 11.0 wt%, or 9.5 wt% to 10.5 wt%, based on the total weight of the top layer, and the middle layer L3 contains yttrium oxide in an amount ranging from 6.0 wt% to 11.0 wt%, 7.5 wt% to 10.5 wt%, or 8.5 wt% to 10.0 wt%, or 9.0 wt% to 9.5 wt%, based on the total weight of the middle layer L3. Yttrium, the intermediate layer L2 contains yttrium oxide in an amount in the range of 4.5 wt% to 9.0 wt%, 5.5 wt% to 8.0 wt%, 6.0 wt% to 7.5 wt% or 6.5 wt% to 7.3 wt%, based on the total weight of the intermediate layer L2, and the bottom layer L1 contains yttrium oxide in an amount in the range of 4.0 wt% to 9.0 wt%, 5.0 wt% to 8.0 wt%, 5.5 wt% to 7.5 wt% or 6.0 wt% to 6.8 wt%, based on the total weight of the bottom layer L1.

[0891]

[79] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[78] ,

[0892] The top layer has an yttrium oxide content based on the total weight of the top layer that is at least 1.0 percentage point, at least 2.0 percentage points, at least 2.5 percentage points, or at least 3.0 percentage points higher than the yttrium oxide content of the bottom layer based on the total weight of the bottom layer.

[0893] The top layer has an yttrium oxide content based on the total weight of the top layer that is at most 8.0 percentage points, at most 6.0 percentage points, at most 5.0 percentage points, or at most 4.0 percentage points higher than the yttrium oxide content of the bottom layer based on the total weight of the bottom layer.

[0894]

[80] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[79] , wherein the top layer has an yttrium oxide content that is at most 1.0 percentage points to 8.0 percentage points, 2.0 percentage points to 6.0 percentage points, 2.5 percentage points to 5.0 percentage points or 3.0 percentage points to 4.0 percentage points higher, based on the total weight of the top layer, than the yttrium oxide content of the bottom layer, based on the total weight of the bottom layer.

[0895]

[81] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[80] , wherein each layer has an yttrium oxide content that differs from the yttrium oxide content of an adjacent layer by at least 0.3 percentage points, at least 0.5 percentage points, at most 3.0 percentage points, at most 2.5 percentage points, or from 0.3 percentage points to 3.0 percentage points or from 0.5 percentage points to 2.5 percentage points, wherein the yttrium oxide content of a layer is based on the total weight of the layer.

[0896]

[82] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[81] , comprising or consisting of:

[0897] a top layer L4, which can be obtained from yttria-stabilized zirconia powder P3,

[0898] an intermediate layer L3, which may be obtained from a mixture of yttria-stabilized zirconium oxide powders P2 and P3,

[0899] an intermediate layer L2, which may be obtained from a mixture of yttria-stabilized zirconium oxide powders P1 and P2,

[0900] a bottom layer L1, which is obtainable from yttria-stabilized zirconia powder P1, and

[0901] The powders P1 to P3 are three yttria-stabilized zirconia powders, wherein powder P1 has an yttria content in the range of 4.5 wt % to 6.1 wt %, powder P2 has an yttria content in the range of 6.2 wt % to 7.9 wt %, and powder P3 has an yttria content in the range of 8.0 wt % to 11.0 wt %.

[0902]

[83] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[82] , comprising or consisting of:

[0903] Top layer L4, which is a pre-sintered top powder layer of powder P3,

[0904] an intermediate layer L3, which is a pre-sintered intermediate powder layer of a mixture of powders P2 / P3,

[0905] an intermediate layer L2, which is a pre-sintered intermediate powder layer of a mixture of powders P1 / P2,

[0906] a bottom layer L1 which is a pre-sintered bottom powder layer of powder P1, and

[0907] The powders P1 to P3 are three yttria-stabilized zirconia powders, wherein powder P1 has an yttria content in the range of 4.5 wt % to 6.1 wt %, powder P2 has an yttria content in the range of 6.2 wt % to 7.9 wt %, and powder P3 has an yttria content in the range of 8.0 wt % to 11.0 wt %.

[0908]

[84] A pre-sintered multilayer dental mill blank according to any of items

[82] and

[83] , wherein the yttrium oxide content of powders P1 and P2 differs by at least 0.7 percentage points, at least 1.0 percentage points, at least 1.2 percentage points, at most 3.0 percentage points, at most 2.8 percentage points, at most 2.5 percentage points, in the range of 0.7 percentage points to 3.0 percentage points, in the range of 1.0 percentage points to 2.8 percentage points, or in the range of 1.2 percentage points to 2.5 percentage points, and the yttrium oxide content of powders P2 and P3 differs by at least 0.7 percentage points, at least 1.0 percentage points, at least 1.2 percentage points, at most 3.0 percentage points, at most 2.8 percentage points, at most 2.5 percentage points, in the range of 0.7 percentage points to 3.0 percentage points, in the range of 1.0 percentage points to 2.8 percentage points, or in the range of 1.2 percentage points to 2.5 percentage points.

[0909]

[85] A pre-sintered multilayer dental mill blank according to any one of items

[82] to

[84] , wherein the mixture of powders P1 / P2 contains powders P1 and P2 in a weight ratio of powder P1 to powder P2 in the range of 10:90 to 40:60, in the range of 15:85 to 35:65, in the range of 20:80 to 30:70 or in the range of 22:78 to 28:72, and / or the mixture of powders P2 / P3 contains powders P2 and P3 in a weight ratio of powder P2 to powder P3 in the range of 10:90 to 40:60, in the range of 15:85 to 35:65, in the range of 20:80 to 30:70 or in the range of 22:78 to 28:72.

[0910]

[86] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[85] , wherein the bottom layer comprises a sintering inhibitor and, optionally, each of the at least one intermediate layer comprises a sintering inhibitor.

[0911]

[87] A pre-sintered multi-layer dental mill blank according to item

[86] , wherein the bottom layer contains the sintering inhibitor in an amount higher than the amount of the sintering inhibitor in the top layer, and optionally, the amount of the sintering inhibitor decreases layer by layer from the bottom layer to the top layer.

[0912]

[88] A pre-sintered multi-layer dental mill blank according to any one of items

[86] and

[75] , wherein the bottom layer comprises the sintering inhibitor in an amount of at least 0.4 wt%, at least 0.6 wt%, at least 0.8 wt%, at most 2.5 wt%, at most 2.0 wt%, at most 1.5 wt%, or in a range of 0.4 wt% to 2.5 wt%, 0.6 wt% to 2.0 wt% or 0.8 wt% to 1.5 wt%, based on the total weight of the bottom layer.

[0913]

[89] The pre-sintered multilayer dental mill blank according to any one of items [1] to

[88] , wherein each of the at least one intermediate layer comprises the sintering inhibitor in an amount of at least 0.02 wt%, at least 0.05 wt%, at most 2.0 wt%, at most 1.5 wt%, at most 1.2, or in the range of 0.02 wt% to 2.0 wt%, 0.05 wt% to 1.5 wt% or 0.05 wt% to 1.2 wt%, based on the total weight of the corresponding layer of the at least one intermediate layer.

[0914]

[90] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[89] , wherein the top layer comprises the sintering inhibitor in an amount by weight of at least 0.01 wt%, at least 0.02 wt%, at least 0.05 wt%, at most 1.0 wt%, at most 0.8 wt%, at most 0.5 wt%, in the range of 0.01 wt% to 1.0 wt%, 0.02 wt% to 0.8 wt% or 0.05 wt% to 0.5 wt%, based on the total weight of the top layer.

[0915]

[91] According to any one of items

[86] to

[90] , the sintering inhibitor can be obtained by converting a sintering inhibitor precursor into the sintering inhibitor when pre-sintering the green body of the multi-layer dental mill blank.

[0916]

[92] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[91] , wherein each layer comprises a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof), and the bottom layer and optionally each of the at least one intermediate layer comprises a sintering inhibitor (e.g., type II yttrium oxide).

[0917]

[93] A pre-sintered multilayer dental mill blank according to any one of items

[86] to

[92] , wherein the sintering inhibitor is La2O3, Yb2O3, Tm2O3, type II yttrium oxide, erbium oxide or any combination thereof, optionally, the sintering inhibitor is La2O3, type II yttrium oxide, erbium oxide or any combination thereof, and optionally, the sintering inhibitor is type II yttrium oxide, erbium oxide or a combination thereof.

[0918]

[94] A pre-sintered multilayer dental mill blank according to any one of items

[86] to

[93] , wherein the sintering inhibitor is type II yttrium oxide, optionally in combination with erbium oxide.

[0919]

[95] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[94] , wherein the top layer has an aluminum content that is the lowest of all the layers,

[0920] Optionally, the aluminum content of the layers increases layer by layer from the top layer in the direction of the bottom layer over at least two layers.

[0921]

[96] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[95] , comprising or consisting of the following layers:

[0922] Top floor L4,

[0923] Middle layer L3,

[0924] Middle layer L2,

[0925] Bottom layer L1,

[0926] wherein the aluminum oxide weight content in each of the layer L1 and the layer L2 is higher than the aluminum oxide weight content in the layer L3, and the aluminum oxide weight content in the layer L3 is higher than the aluminum oxide weight content in the layer L4,

[0927] The aluminum oxide weight content of a layer is determined based on the total weight of the respective layer.

[0928]

[97] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[96] , wherein the bottom layer comprises at least 0.01 wt%, at least 0.02 wt% or at least 0.05 wt% of aluminum oxide, based on the total weight of the bottom layer, and / or at most 0.50 wt%, at most 0.40 wt%, at most 0.20 wt% or at most 0.15 wt% of aluminum oxide, based on the total weight of the bottom layer.

[0929]

[98] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[97] , wherein the bottom layer comprises 0.01 wt% to 0.50 wt%, 0.02 wt% to 0.40 wt% or 0.05 wt% to 0.20 wt% of aluminum oxide, based on the total weight of the bottom layer.

[0930]

[99] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[98] , wherein each layer comprises a colored metal oxide.

[0931]

[100] The pre-sintered multilayer dental mill blank according to item

[99] , each layer comprising the colored metal oxide in an amount of at least 0.01 wt%, 0.02 wt%, at least 0.05 wt%, at most 1.5 wt%, at most 1.2 wt%, at most 1.0 wt%, or in the range of 0.01 wt% to 1.5 wt%, in the range of 0.02 wt% to 1.2 wt%, or in the range of 0.05 wt% to 1.0 wt%, based on the total weight of the corresponding layer.

[0932]

[101] The pre-sintered multilayer dental mill blank according to item

[99] or

[100] , wherein the colored metal oxide comprises iron oxide, manganese oxide, praseodymium oxide, chromium oxide, erbium oxide, terbium oxide or a mixture thereof.

[0933]

[102] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[101] , wherein the bottom layer comprises

[0934] 85 to 94 wt%, such as in the range of 88 to 94 wt%, such as in the range of 90 to 92 wt% zirconium oxide,

[0935] ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0936] 0.01 to 0.50 wt%, such as in the range of 0.02 to 0.40 wt%, such as in the range of 0.05 to 0.20 wt% alumina,

[0937] 4.0 to 9.0 wt%, such as in the range of 5.0 to 8.0 wt%, such as in the range of 5.5 to 7.5 wt% of yttrium oxide,

[0938] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide,

[0939] 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.05 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0940] Each is based on the total weight of the base layer, wherein the weight amounts of the components are optionally selected to total 100 wt%.

[0941]

[103] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[102] , wherein the top layer comprises

[0942] 80% to 92% by weight, such as in the range of 85% to 91% by weight, such as in the range of 87% to 90% by weight of zirconium oxide,

[0943] ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0944] 7.0 to 13.0 wt%, such as in the range of 8.0 to 12.0 wt%, such as in the range of 9.0 to 11.0 wt% yttrium oxide,

[0945] <0.01 wt.% aluminum oxide,

[0946] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide,

[0947] 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.10 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0948] Each is based on the total weight of the top layer, wherein the weight amounts of the components are optionally selected to total 100 wt%.

[0949]

[104] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[103] , wherein each of the at least one intermediate layer comprises

[0950] 82 to 94 wt%, such as in the range of 85 to 93 wt%, such as in the range of 87 to 92 wt% zirconium oxide,

[0951] ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0952] 0.01 to 0.50 wt%, such as in the range of 0.02 to 0.20 wt%, such as in the range of 0.02 to 0.15 wt% alumina,

[0953] 5.0% to 11.0% by weight, such as in the range of 6.0% to 10.5% by weight, such as in the range of 6.5% to 10.0% by weight of yttrium oxide,

[0954] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide,

[0955] 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.05 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0956] Each is based on the total weight of the respective layer of the at least one intermediate layer, wherein the weight amounts of the components are optionally selected to total 100 wt%.

[0957]

[105] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[104] , comprising or consisting of the following layers: a top layer L4, a middle layer L3, a middle layer L2 and a bottom layer L1, and the layers L4 to L1 comprise the components as defined in any one of Table I, Table Ib, Table II, Table III and Table IV herein.

[0958]

[106] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[105] , comprising yttria-stabilized zirconia in an amount of at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 97 wt%, or in the range of 80 wt% to 99.5 wt%, 90 wt% to 99.5 wt%, 95 wt% to 99.0 wt%, or 97 wt% to 98.5 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0959]

[107] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[106] , comprising zirconium oxide, yttrium oxide and hafnium dioxide in a combined weight amount of at least 90 wt%, at least 95 wt%, at least 98 wt%, at most 99.8 wt%, at most 99.4 wt%, at most 99.2 wt%, or in the range of 90 wt% to 99.8 wt%, 95 wt% to 99.5 wt%, or 98 wt% to 99.2 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0960]

[108] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[107] , comprising aluminium oxide in an amount by weight of at least 0.005 wt%, at least 0.02 wt% or at least 0.05 wt%, at most 0.4 wt%, at most 0.2 wt% or at most 0.1 wt%, or in the range of 0.005 wt% to 0.4 wt%, 0.02 wt% to 0.2 wt% or 0.05 wt% to 0.1 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0961]

[109] The pre-sintered multilayer dental mill blank according to any one of items [1] to

[108] , which is pre-colored and optionally comprises a colored metal oxide in an amount by weight of at least 0.01 wt%, at least 0.02 wt%, at least 0.05 wt%, at most 1.5 wt%, at most 1.0 wt%, at most 0.8 wt%, or in the range of 0.01 wt% to 1.5 wt%, 0.02 wt% to 1.0 wt%, or 0.05 wt% to 0.8 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0962]

[110] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[109] , comprising a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof) in an amount by weight of at least 0.02 wt%, at least 0.05 wt%, at least 0.10 wt%, at most 0.15 wt%, at most 0.8 wt%, at most 0.45 wt%, at most 0.30 wt%, or at most 0.25 wt%, or in a range of 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.45 wt%, 0.10 wt% to 0.30 wt%, or 0.15 wt% to 0.25 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0963]

[111] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[110] , comprising a sintering inhibitor (e.g., type II yttrium oxide, optionally in combination with erbium oxide) in an amount by weight of at least 0.1 wt%, at least 0.2 wt%, at least 0.3 wt%, at least 0.5 wt%, at most 2.5 wt%, at most 2.0 wt%, at most 1.5 wt% or at most 1.2 wt%, or in a range of 0.1 wt% to 2.5 wt%, 0.2 wt% to 2.0 wt%, 0.3 wt% to 1.5 wt% or 0.5 wt% to 1.2 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0964]

[112] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[111] , comprising

[0965] 80% to 95% by weight, such as in the range of 85% to 93% by weight, such as in the range of 89% to 91% by weight, zirconium oxide,

[0966] ≤5 wt%, such as ≤3 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide,

[0967] 5.0% to 10.0% by weight, such as in the range of 6.0% to 9.0% by weight, such as in the range of 6.5% to 8.5% by weight of yttrium oxide,

[0968] ≤ 0.4 wt %, such as in the range of 0.02 wt % to 0.2 wt %, such as in the range of 0.05 wt % to 0.1 wt % aluminum oxide,

[0969] 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.0 wt%, such as in the range of 0.05 to 0.8 wt% of colored metal oxide,

[0970] 0.02 wt% to 0.8 wt%, 0.05 wt% to 0.45 wt%, 0.10 wt% to 0.30 wt% of a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof),

[0971] Each is based on the total weight of the pre-sintered multilayer dental mill blank, and the weight amounts of the components therein are optionally selected to total 100 wt%.

[0972]

[113] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[112] , characterized in that a representative test cross-section of each layer is provided, and when fully sintered by a rapid sintering method, the representative test cross-section of the top layer and the representative test cross-section of the bottom layer each have a maximum sintering rate at the temperature T of the rapid sintering method, and the top layer (T TL ) and the bottom layer (T BL ) differ by no more than 40°C or no more than 25°C, optionally, when fully sintered by the rapid sintering method, a representative test cross-section of each layer has a maximum sintering rate at the temperature T of the rapid sintering method, and the temperature T of each of the layers differs by no more than 40°C or no more than 25°C.

[0973]

[114] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[113] , characterized in that a test cross-section of the top layer is provided, and when fully sintered by a rapid sintering method, a representative test cross-section of the top layer has a flexural strength of at least 500 MPa, at least 550 MPa, at least 575 MPa, at least 600 MPa, at most 1100 MPa, at most 1000 MPa, at most 800 MPa or at most 750 MPa, or in the range of 500 MPa to 1100 MPa, 550 MPa to 1000 MPa, 575 MPa to 800 MPa or 600 MPa to 750 MPa.

[0974]

[115] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[114] , characterized in that a test section of the bottom layer is provided, and when fully sintered by a rapid sintering method, a representative test section of the bottom layer has a flexural strength of at least 900 MPa, at least 1000 MPa, at least 1050 MPa, at most 1500 MPa, at most 1300 MPa, at most 1200 MPa, or in the range of 900 MPa to 1500 MPa, 1000 MPa to 1300 MPa or 1050 MPa to 1200 MPa.

[0975]

[116] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[115] , characterised in that a test cross section of the top layer is provided, and when fully sintered by a rapid sintering method, a representative test cross section of the top layer has a strength of at least 2.5 MPa*m 1 / 2 , at least 2.7 MPa*m 1 / 2 , at least 2.8 MPa*m 1 / 2 , up to 3.5 MPa*m 1 / 2 , up to 3.3MPa*m 1 / 2 or up to 3.2 MPa*m 1 / 2 , or between 2.5 and 3.5 MPa*m 1 / 2 , 2.7 to 3.3 MPa*m 1 / 2 or 2.8 to 3.2 MPa*m 1 / 2 The fracture toughness K in the range IC .

[0976]

[117] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[116] , characterised in that a test cross section of the bottom layer is provided, and when fully sintered by a rapid sintering method, a representative test cross section of the bottom layer has a strength of at least 3.6 MPa*m 1 / 2 , at least 3.8 MPa*m 1 / 2 , at least 4.0 MPa*m 1 / 2 , up to 5.5 MPa*m 1 / 2 , up to 4.8MPa*m 1 / 2 , up to 4.6 MPa*m 1 / 2 or up to 4.4 MPa*m 1 / 2 , or between 3.6 and 5.5 MPa*m 1 / 2 , 3.8 to 4.8 MPa*m 1 / 2 , 4.0 to 4.6 MPa*m 1 / 2 or 4.0 to 4.4 MPa*m 1 / 2 The fracture toughness K in the rangeIC .

[0977]

[118] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[117] , comprising or consisting of a top layer L4, an intermediate layer L3, an intermediate layer L2, a bottom layer L1, wherein a representative test section of the layer, when fully sintered by a rapid sintering method, may have a fracture toughness K IC :

[0978] 2.5 to 3.5 MPa*m measured with a load of 2.5 kg 1 / 2 , 2.7 to 3.3 MPa*m 1 / 2 or 2.8 to 3.2 MPa*m 1 / 2 The top layer L4 within the range,

[0979] 2.6 to 3.6 MPa*m measured with a 5 kg load 1 / 2 , 2.8 to 3.4 MPa*m 1 / 2 or 2.9 to 3.3 MPa*m 1 / 2 The range of the middle layer L3,

[0980] 3.1 to 4.2 MPa*m measured with a 5 kg load 1 / 2 , 3.3 to 4.0 MPa*m 1 / 2 or 3.4 to 3.8 MPa*m 1 / 2 The range of the middle layer L2,

[0981] 3.6 to 4.8 MPa*m measured with a 10 kg load 1 / 2 , 3.8 to 4.6 MPa*m 1 / 2 or 3.9 to 4.4 MPa*m 1 / 2 within the scope of the bottom layer.

[0982]

[119] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[118] , wherein the rapid sintering method is a sintering method having a total duration of less than 25 minutes and a maximum sintering temperature in the range of 1350°C to 1650°C.

[0983]

[120] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[119] , wherein the rapid sintering method is a sintering method consisting of the following steps:

[0984] - a first heating step starting from 25 °C at a heating rate of 200 K / min and ending at 1050 °C,

[0985] - a second heating step starting at 1050 °C and ending at 1450 °C at a heating rate of 100 K / min,

[0986] - a hold step where the temperature is kept at 1450°C for 2 minutes,

[0987] - a first cooling step starting from 1450°C and ending at 1350°C at a cooling rate of 130 K / min,

[0988] - a second cooling step starting from 1350°C and ending at 1200°C at a cooling rate of 70 K / min, followed by cooling, and

[0989] wherein the first heating step and the second heating step are performed by applying a vacuum at a pressure in the range of 50 mbar to 100 mbar (e.g. 80 mbar) until a temperature of 1400°C is reached, and once the temperature of 1400°C is reached, the vacuum is exchanged with air.

[0990]

[121] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[120] , comprising at least two intermediate layers, and

[0991] Optionally composed of a top layer L4, a middle layer L3, a middle layer L2 and a bottom layer L1.

[0992]

[122] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[121] , wherein the bottom layer has a height of at least 30%, at least 40%, at least 45%, at least 50% or at least 52% relative to the total height of the pre-sintered multi-layer dental mill blank, and / or a height of at most 75%, at most 70%, at most 68% or at most 66% relative to the total height of the pre-sintered multi-layer dental mill blank,

[0993] Or the bottom layer has a height in the range of 30% to 75%, 40% to 75%, 45% to 70%, 50% to 68% or 52% to 66% relative to the total height of the pre-sintered multi-layer dental mill blank.

[0994]

[123] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[122] , wherein the top layer has a height in the range of 8% to 35%, 10% to 30%, 12% to 28%, 15% to 25% or 17% to 23% relative to the total height of the pre-sintered multi-layer dental mill blank, or

[0995] The top layer has a height of at least 8%, at least 10%, at least 12%, at least 15% or at least 17% relative to the total height of the pre-sintered multi-layer dental mill blank and / or the top layer has a height of at most 35%, at most 30%, at most 28%, at most 25%, at most 23% relative to the total height of the pre-sintered multi-layer dental mill blank.

[0996]

[124] The pre-sintered multi-layer dental mill blank according to any one of items [1] to

[123] , wherein each of the at least one intermediate layer has a height in the range of 2 to 25%, 4 to 20%, 6 to 15% or 8 to 12% relative to the total height of the pre-sintered multi-layer dental mill blank, and / or the combined intermediate layer has a height in the range of 5 to 40%, 10 to 30%, 14 to 26% or 16 to 25% relative to the total height of the pre-sintered multi-layer dental mill blank.

[0997]

[125] A pre-sintered multilayer dental mill blank according to any one of items [1] to

[124] , having a density of at least 45%, at least 50%, at least 52%, at most 70%, at most 60%, at most 55%, such as in the range of 45% to 70%, 50% to 60% or 52% to 55% relative to its theoretical density.

[0998]

[126] A pre-sintered multi-layer dental mill blank according to any one of items [1] to

[125] , which can be obtained by pre-sintering a green body of the pre-sintered multi-layer dental mill blank at a maximum pre-sintering temperature of at least 700°C, at least 750°C, at least 800°C, at least 825°C, 1100°C, at most 1000°C, at most 950°C, at most 900°C, such as in the range of 700°C to 1100°C, in the range of 750°C to 1000°C, in the range of 800°C to 950°C or in the range of 825°C to 900°C.

[0999]

[127] A pre-sintered multi-layer dental mill blank, which can be obtained by a method according to any one of items

[128] to

[147] .

[1000]

[128] A method for preparing a pre-sintered multi-layer dental mill blank, the method comprising the following steps:

[1001] a) providing three yttria-stabilized zirconium oxide powders P1 to P3, powder P1 having an yttria content in the range of 4.5% to 6.1% by weight, powder P2 having an yttria content in the range of 6.2% to 7.9% by weight, and powder P3 having an yttria content in the range of 8.0% to 11.0% by weight,

[1002] b) preparing a green body comprising or consisting of:

[1003] The top powder layer of powder P3,

[1004] at least one intermediate powder layer of a powder mixture chosen from a mixture of powders P2 / P3 and a mixture of powders P1 / P2,

[1005] a bottom powder layer of powder P1 or a mixture of powders P1 / P2,

[1006] c) pre-sintering the green body to provide a pre-sintered multi-layer dental mill blank.

[1007]

[129] The method according to item

[128] , wherein the green body comprises or consists of:

[1008] The top powder layer of powder P3,

[1009] An intermediate powder layer of a mixture of powders P2 / P3,

[1010] An intermediate powder layer of a mixture of powders P1 / P2,

[1011] Bottom powder layer of powder P1.

[1012]

[130] According to the method described in any of items

[128] and

[129] , the yttrium oxide content of powders P1 and P2 differs by at least 0.7 percentage points, at least 1.0 percentage points, at least 1.2 percentage points, at most 3.0 percentage points, at most 2.8 percentage points, at most 2.5 percentage points, in the range of 0.7 percentage points to 3.0 percentage points, in the range of 1.0 percentage points to 2.8 percentage points or in the range of 1.2 percentage points to 2.5 percentage points, and the yttrium oxide content of powders P2 and P3 differs by at least 0.7 percentage points, at least 1.0 percentage points, at least 1.2 percentage points, at most 3.0 percentage points, at most 2.8 percentage points, at most 2.5 percentage points, in the range of 0.7 percentage points to 3.0 percentage points, in the range of 1.0 percentage points to 2.8 percentage points or in the range of 1.2 percentage points to 2.5 percentage points.

[1013]

[131] The method according to any one of items

[128] to

[130] , wherein the powder P1 has an yttrium oxide content in the range of 4.9 wt% to 6.0 wt%, or the powder P2 has an yttrium oxide content in the range of 6.5 wt% to 7.6 wt%, or the powder P3 has an yttrium oxide content in the range of 9.0 wt% to 10.5 wt%, optionally the powder P1 has an yttrium oxide content in the range of 4.9 wt% to 6.0 wt%, the powder P2 has an yttrium oxide content in the range of 6.5 wt% to 7.6 wt%, and the powder P3 has an yttrium oxide content in the range of 9.0 wt% to 10.5 wt%.

[1014]

[132] The method according to any one of items

[128] to

[132] , wherein the mixture of powders P2 / P3 contains powders P2 and P3 in a weight ratio [powder P2:powder P3] in the range of 10:90 to 40:60, in the range of 15:85 to 35:65 or in the range of 20:80 to 30:70, and / or

[1015] The mixture of powders P1 / P2 contains powders P1 and P2 in a weight ratio [powder P1:powder P2] within a range of 10:90 to 40:60, within a range of 15:85 to 35:65, or within a range of 20:80 to 30:70.

[1016]

[133] A method according to any one of items

[128] to

[133] , comprising adding one or more additives to the powders P1 to P3 or a mixture thereof, the additives being selected from the group consisting of: a sintering inhibitor precursor, a sintering inhibitor precursor and a coloring additive.

[1017]

[134] According to the method described in item

[120] , the one or more additives are added to the powders P1 to P3 before preparing the powder mixtures of powders P1 / P2 and powders P2 / P3.

[1018]

[135] A method according to any one of items

[128] to

[134] , comprising adding a sintering activator precursor to at least powder P3 or a mixture thereof, optionally to the powders P1 to P3 or a mixture thereof.

[1019]

[136] According to the method described in item

[135] , the top powder layer has a weight content of the sintering activator precursor that is higher than the weight content of the sintering activator precursor in the bottom layer, and optionally, the weight content of the sintering activator precursor increases layer by layer from the bottom powder layer to the top powder layer.

[1020]

[137] According to the method described in any one of items

[135] and

[136] , the sintering activator precursor is a zinc salt, a gallium salt or a combination thereof.

[1021]

[138] The method according to any one of items

[128] to

[137] , comprising adding at least a sintering inhibitor precursor to the powder P1 or a mixture thereof,

[1022] Optionally added to the powders P1 and P2 or their mixture.

[1023]

[139] According to the method of item

[138] , the bottom powder layer has a weight content of the sintering inhibitor precursor higher than the weight content of the sintering inhibitor precursor in the top layer, and optionally, the weight content of the sintering inhibitor precursor decreases layer by layer from the bottom powder layer to the top powder layer.

[1024]

[140] According to the method of any one of items

[138] and

[139] , the sintering inhibitor precursor is a yttrium salt, an erbium salt, a lanthanum salt, a ytterbium salt, a thulium salt or any combination thereof, optionally the sintering inhibitor precursor is a yttrium salt, an erbium salt, a lanthanum salt or any combination thereof, optionally the sintering inhibitor precursor is a yttrium salt, an erbium salt or any combination thereof.

[1025]

[141] A method according to any one of items

[138] to

[140] , wherein the sintering inhibitor precursor is a yttrium salt, optionally in combination with an erbium salt.

[1026]

[142] A method according to any one of items

[128] to

[141] , wherein the method does not include adding yttrium salt to the powder P3.

[1027]

[143] The method according to any one of items

[128] to

[142] , comprising adding a coloring additive to the powders P1 to P3 or their mixture.

[1028]

[144] The method according to item

[143] , wherein the coloring additive comprises an erbium compound and an iron compound.

[1029]

[145] According to the method of any one of items

[128] to

[144] , the preparation of the green body comprises compacting (e.g., pressing) the powder layer, optionally at a pressure in the range of 200 MPa to 400 MPa, such as in the range of 250 MPa to 350 MPa.

[1030]

[146] According to the method of any one of items

[128] to

[145] , the pre-sintering has a maximum temperature of at least 700°C, at least 750°C, at least 800°C, at least 825°C, at most 1100°C, at most 1000°C, at most 950°C, at most 900°C, or in the range of 700°C to 1100°C, in the range of 750°C to 1000°C, in the range of 800°C to 950°C, or in the range of 825°C to 900°C.

[1031]

[147] A method according to any one of items

[128] to

[146] , wherein the method is a method for preparing a pre-sintered multi-layer dental mill blank according to any one of items [1] to

[126] .

[1032]

[148] A method for preparing a dental restoration, the method comprising the following steps:

[1033] - machining the pre-sintered multilayer dental mill blank according to any one of items [1] to

[127] to provide a dental restoration precursor;

[1034] - optionally surface treating the dental restoration precursor; and

[1035] - sintering the dental restoration precursor to provide a dental restoration.

[1036]

[149] According to the method described in item

[148] , the machining is performed using a CAD / CAM method.

[1037]

[150] A dental restoration obtainable by the method for preparing a dental restoration according to item

[148] or item

[149] .

[1038]

[151] A method for sintering a dental restoration precursor,

[1039] The method has a total duration of less than 25 minutes and a maximum sintering temperature in the range of 1350° C. to 1650° C.,

[1040] The method comprises subjecting the dental restoration precursor to

[1041] (i) heat treatment, and

[1042] (ii) cooling treatment,

[1043] The cooling process comprises a cooling step A,

[1044] The cooling step A starts and ends in a temperature range between 1100° C. and the maximum sintering temperature and has a cooling rate A of at least 75 K / min.

[1045]

[152] The method of item

[151] , having a total duration of less than 20 minutes, less than 18 minutes, less than 16 minutes or less than 15 minutes, such as in the range of 5 minutes to less than 20 minutes, 8 minutes to less than 18 minutes, 10 minutes to less than 16 minutes or 12 minutes to less than 15 minutes.

[1046]

[153] The method according to item

[151] or

[152] , which has a maximum sintering temperature in the range of 1400°C to 1600°C, in the range of 1400°C to 1560°C, in the range of 1400°C to 1500°C, or in the range of 1425°C to 1475°C.

[1047]

[154] According to the method of any one of items

[151] to

[153] , the cooling rate A is at least 100 K / min, at least 110 K / min, at least 120 K / min, at most 250 K / min, at most 200 K / min, at most 160 K / min, in the range of 100 K / min to 250 K / min, in the range of 110 K / min to 180 K / min or in the range of 120 K / min to 160 K / min.

[1048]

[155] According to the method described in any one of items

[151] to

[154] , the cooling step A starts and ends within a temperature range between 1200°C and the maximum sintering temperature, or within a temperature range between 1250°C and the maximum sintering temperature, or within a temperature range between 1300°C and the maximum sintering temperature.

[1049]

[156] According to the method described in any one of items

[151] to

[155] , the cooling treatment includes a cooling step B after the cooling step A, and the cooling step B has a cooling rate B lower than that of the cooling step A.

[1050]

[157] The method according to item

[156] , wherein the cooling rate B is at least 30 K / min, at least 50 K / min, at least 60 K / min, at most 110 K / min, at most 90 K / min, at most 80 K / min, in the range of 30 K / min to 110 K / min, in the range of 50 K / min to 90 K / min or in the range of 60 K / min to 80 K / min.

[1051]

[158] According to the method described in any one of items

[156] and

[157] , the cooling step B starts and ends within a temperature range between 1000°C and the end temperature of the cooling step A, or within a temperature range between 1100°C and the end temperature of the cooling step A, or within a temperature range between 1150°C and the end temperature of the cooling step A, or within a temperature range between 1200°C and the end temperature of the cooling step A.

[1052]

[159] According to the method described in any one of items

[151] to

[158] , the cooling treatment includes a cooling step C after the cooling step A or after the cooling step B, wherein the cooling step C has a cooling rate C of at most 20 K / min, at most 10 K / min, at most 5 K / min or about 0 K / min (i.e., the cooling step C is a holding step).

[1053]

[160] According to the method of any one of items

[151] to

[159] , the cooling treatment ends at a final temperature and is subsequently cooled, and the final temperature of the cooling treatment is at least 1000°C, at least 1100°C, at least 1150°C, at most 1300°C, at most 1280°C, at most 1250°C, in the range of 1000°C to 1300°C, in the range of 1100°C to 1280°C or in the range of 1150°C to 1250°C.

[1054]

[161] According to the method described in any one of items

[151] to

[160] , the heating treatment includes a heating step A, wherein the heating step A has a heating rate A of at least 150 K / min, at least 170 K / min, at least 190 K / min, at most 300 K / min, at most 250 K / min, at most 220 K / min, in the range of 150 K / min to 300 K / min, in the range of 170 K / min to 250 K / min, or in the range of 190 K / min to 220 K / min.

[1055]

[162] The method according to item

[161] , wherein the heating treatment includes a heating step B after the heating step A, the heating step B having a heating rate B lower than the heating rate A, and the heating rate B is at least 50 K / min, at least 70 K / min, at least 90 K / min, at most 200 K / min, at most 150 K / min, at most 120 K / min, in the range of 50 K / min to 200 K / min, in the range of 70 K / min to 150 K / min or in the range of 90 K / min to 120 K / min.

[1056]

[163] According to the method described in any one of items

[151] to

[162] , the heating treatment includes a heating step C carried out at the maximum sintering temperature and having a heating rate of about 0 K / min (i.e., the heating step C is a holding step at the maximum sintering speed), and optionally, the maximum sintering temperature is maintained in the heating step C for at least 30 seconds, at least 1 minute, at most 5 minutes, at most 3 minutes, in the range of 30 seconds to 5 minutes or in the range of 1 minute to 3 minutes.

[1057]

[164] According to the method of any one of items

[151] to

[163] , the heat treatment is at least partially carried out at a pressure of 500 mbar or less, 200 mbar or less, 150 mbar or less, 100 mbar or less, such as in the range of 0.1 mbar to 500 mbar, 1 mbar to 200 mbar, 10 mbar to 150 mbar or 50 mbar to 100 mbar.

[1058]

[165] The method according to any one of items

[151] to

[164] , wherein the dental restoration precursor is pre-sintered and / or has a density of at least 45%, at least 50%, at least 52%, at most 70%, at most 60%, at most 55%, such as in the range of 45% to 70%, 50% to 60% or 52% to 55% relative to its theoretical density.

[1059]

[166] The method according to any one of items

[151] to

[165] , wherein the dental restoration precursor comprises zirconium oxide and yttrium oxide, and optionally, the dental restoration precursor comprises at least three sections, and each section comprises zirconium oxide and yttrium oxide, and each section has a different yttrium oxide content.

[1060]

[167] A method according to any one of items

[151] to

[166] , wherein the dental restoration precursor comprises a colouring oxide, and optionally the colouring oxide comprises iron oxide.

[1061]

[168] According to the method of any one of items [151...

Claims

1. A pre-sintered multi-layer dental grinding blank comprising Top floor, bottom layer, and At least one intermediate layer, Each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, and The top layer comprises a sintering activator, which is zinc oxide, gallium oxide, or a combination thereof.

2. The pre-sintered multi-layer dental mill blank of claim 1 , wherein the yttria content of the layers increases such that the bottom layer has a lower yttria content than the at least one intermediate layer, and the at least one intermediate layer has a lower yttria content than the top layer.

3. The pre-sintered multi-layer dental mill blank according to claim 1 or 2, wherein the yttrium oxide content of the layers increases layer by layer from the bottom layer to the top layer.

4. The pre-sintered multilayer dental mill blank according to any one of claims 1 to 3, wherein the top layer comprises aluminum oxide in an amount of less than 0.05 wt%, or less than 0.02 wt%, or less than 0.01 wt%, based on the total weight of the top layer.

5. A pre-sintered multi-layer dental grinding blank comprising Top floor, bottom layer, and At least one intermediate layer, Each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, and The top layer comprises aluminum oxide in an amount less than 0.01 wt %, based on the total weight of the top layer.

6. The pre-sintered multi-layer dental mill blank of claim 5, wherein the yttria content of the layers increases such that the bottom layer has a lower yttria content than the at least one intermediate layer, and the at least one intermediate layer has a lower yttria content than the top layer.

7. The pre-sintered multi-layer dental mill blank according to claim 5 or 6, wherein the yttrium oxide content of the layers increases layer by layer from the bottom layer to the top layer.

8. The pre-sintered multi-layer dental mill blank according to any one of claims 5 to 7, wherein the top layer comprises a sintering activator selected from the group consisting of zinc oxide, gallium oxide, and combinations thereof.

9. The pre-sintered multilayer dental mill blank according to any one of claims 1 to 8, each layer comprising a sintering activator selected from the group consisting of zinc oxide, gallium oxide, and combinations thereof.

10. The pre-sintered multi-layer dental mill blank according to any one of claims 1 to 9, wherein the bottom layer comprises a sintering inhibitor, which is yttrium oxide obtainable by converting a sintering inhibitor precursor, which is an yttrium salt, into the sintering inhibitor during pre-sintering of the green body of the multi-layer dental mill blank.

11. The pre-sintered multi-layer dental mill blank according to any one of claims 1 to 10, comprising the following layers: Top floor L4, Middle layer L3, Middle layer L2, Bottom layer L1, the top layer L4 comprises yttrium oxide in an amount by weight ranging from 7.0 wt% to 13.0 wt%, from 8.0 wt% to 12.0 wt%, from 9.0 wt% to 11.0 wt%, or from 9.5 wt% to 10.5 wt%, based on the total weight of the top layer, the intermediate layer L3 contains yttrium oxide in an amount by weight ranging from 6.0 wt % to 11.0 wt %, from 7.5 wt % to 10.5 wt %, from 8.5 wt % to 10.0 wt %, or from 9.0 wt % to 9.5 wt %, based on the total weight of the intermediate layer L3, The intermediate layer L2 contains yttrium oxide in an amount by weight ranging from 4.5 wt% to 9.0 wt%, 5.5 wt% to 8.0 wt%, 6.0 wt% to 7.5 wt%, or 6.5 wt% to 7.3 wt%, based on the total weight of the intermediate layer L2, and The underlayer L1 includes yttrium oxide in an amount by weight ranging from 4.0 wt% to 9.0 wt%, 5.0 wt% to 8.0 wt%, 5.5 wt% to 7.5 wt%, or 6.0 wt% to 6.8 wt%, based on the total weight of the underlayer L1.

12. The pre-sintered multilayer dental mill blank according to any one of claims 1 to 11, the top layer comprising yttrium oxide in an amount by weight ranging from 9.0 wt.-% to 12.0 wt.-%, based on the total weight of the top layer, The base layer includes yttrium oxide in an amount ranging from 5.5 wt % to 7.5 wt % based on the total weight of the base layer.

13. The pre-sintered multi-layer dental mill blank according to any one of claims 1 to 12, comprising: a top layer L4, which can be obtained from yttria-stabilized zirconia powder P3, an intermediate layer L3, which may be obtained from a mixture of yttria-stabilized zirconium oxide powders P2 and P3, an intermediate layer L2, which may be obtained from a mixture of yttria-stabilized zirconium oxide powders P1 and P2, a bottom layer L1, which is obtainable from yttria-stabilized zirconia powder P1, and The powder P1 has an yttrium oxide content ranging from 4.5 wt % to 6.1 wt %, the powder P2 has an yttrium oxide content ranging from 6.2 wt % to 7.9 wt %, and the powder P3 has an yttrium oxide content ranging from 8.0 wt % to 11.0 wt %.

14. The pre-sintered multi-layer dental mill blank according to any one of claims 1 to 13, which is pre-colored.

15. The pre-sintered multi-layer dental mill blank according to any one of claims 1 to 14, wherein the top layer comprises 80% to 92% by weight, such as in the range of 85% to 91% by weight, such as in the range of 87% to 90% by weight of zirconium oxide, ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide, 7.0 to 13.0 wt%, such as in the range of 8.0 to 12.0 wt%, such as in the range of 9.0 to 11.0 wt% yttrium oxide, <0.01 wt.% aluminum oxide, 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide, 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.10 wt% to 0.30 wt% of a sintering activator which is zinc oxide, gallium oxide, or a combination thereof, All are based on the total weight of the top layer.

16. The pre-sintered multi-layer dental mill blank according to any one of claims 1 to 15, wherein the bottom layer comprises 85 to 94 wt%, such as in the range of 88 to 94 wt%, such as in the range of 90 to 92 wt% zirconium oxide, ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide, 0.01 to 0.50 wt%, such as in the range of 0.02 to 0.40 wt%, such as in the range of 0.05 to 0.20 wt% alumina, 4.0 to 9.0 wt%, such as in the range of 5.0 to 8.0 wt%, such as in the range of 5.5 to 7.5 wt% yttrium oxide, 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide, 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.05 wt% to 0.30 wt% of a sintering activator which is zinc oxide, gallium oxide, or a combination thereof, All are based on the total weight of the substrate.

17. The pre-sintered multi-layer dental mill blank according to any one of claims 1 to 16, each of the at least one intermediate layer comprising 82 to 94 wt%, such as in the range of 85 to 93 wt%, such as in the range of 87 to 92 wt% zirconium oxide, ≤5.0 wt%, such as ≤3.0 wt%, such as in the range of 0.5 wt% to 3.0 wt% hafnium dioxide, 0.01 to 0.50 wt%, such as in the range of 0.02 to 0.20 wt%, such as in the range of 0.02 to 0.15 wt% alumina, 5.0 to 11.0 wt%, such as in the range of 6.0 to 10.5 wt%, such as in the range of 6.5 to 10.0 wt% yttrium oxide, 0.01 to 1.5 wt%, such as in the range of 0.02 to 1.2 wt%, such as in the range of 0.05 to 1.0 wt% of colored metal oxide, 0.02 wt% to 0.80 wt%, such as in the range of 0.02 wt% to 0.50 wt%, such as in the range of 0.05 wt% to 0.30 wt% of a sintering activator which is zinc oxide, gallium oxide, or a combination thereof, Each is based on the total weight of the corresponding layer of the at least one intermediate layer.

18. The pre-sintered multi-layer dental mill blank according to any one of claims 1 to 17, consisting of: Top floor L4, Middle layer L3, the middle layer L2, and Bottom layer L1, And said layers L4 to L1 comprise the components as defined in Table 1b, wherein the indicated weight amounts are based on the total weight of the corresponding layer: Table Ib: 。 19. A pre-sintered multi-layer dental grinding blank comprising Top floor, bottom layer, and At least one intermediate layer, The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer, When fully sintered by the flash sintering method, the representative test cross section has increasing contrast from the top layer to the bottom layer.

20. The pre-sintered multi-layer dental mill blank of claim 19, wherein the contrast increases from the top layer to the bottom layer such that the contrast of the top layer is lower than the contrast of the at least one intermediate layer, and the contrast of the at least one intermediate layer is lower than the contrast of the bottom layer.

21. The pre-sintered multi-layer dental mill blank according to claim 19 or 20, wherein the contrast increases layer by layer from the top layer to the bottom layer.

22. The pre-sintered multi-layer dental mill blank according to any one of claims 19 to 21, wherein the contrast [%] of the bottom layer differs from the contrast [%] of the top layer by at least 5 percentage points when measured at a sample thickness of 0.8 mm.

23. The pre-sintered multi-layer dental mill blank according to any one of claims 19 to 22, comprising the following layers: a top layer L4, a middle layer L3, a middle layer L2, a bottom layer L1, and the contrast of said layers satisfies one or more of the contrast profiles A1.1 to J1.1 as defined in Table A1 herein Table A1: 。 24. A pre-sintered multi-layer dental mill blank comprising Top floor, bottom layer, and At least one intermediate layer, The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer, When fully sintered by the flash sintering method, the representative test cross-section has a CIE lightness L* that increases from the bottom layer to the top layer.

25. The pre-sintered multi-layer dental mill blank according to claim 24, wherein the CIE brightness L* increases from the bottom layer to the top layer, such that the CIE brightness L* of the bottom layer is lower than the CIE brightness L* of the at least one intermediate layer, and the CIE brightness L* of the at least one intermediate layer is lower than the CIE brightness L* of the bottom layer.

26. The pre-sintered multi-layer dental mill blank according to claim 24 or 25, wherein the CIE brightness L* increases layer by layer from the top layer to the bottom layer.

27. A pre-sintered multilayer dental mill blank according to any one of claims 19 to 26, each layer comprising zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer.

28. The pre-sintered multi-layer dental mill blank of claim 27, the yttria content of the layers increasing from a bottom layer to a top layer, such that the bottom layer has a lower yttria content than the at least one intermediate layer, and the at least one intermediate layer has a lower yttria content than the top layer.

29. The pre-sintered multi-layer dental mill blank according to claim 27 or 28, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer.

30. A pre-sintered multi-layer dental mill blank comprising Top floor, bottom layer, and At least one intermediate layer, each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, The pre-sintered multi-layer dental mill blank is characterized by providing a representative test cross-section of each layer, and A representative tested cross section of the top layer and / or an intermediate layer adjacent to the top layer has a pore count per grain of less than 0.25 when fully sintered by a flash sintering process.

31. The pre-sintered multi-layer dental mill blank of claim 30, wherein the yttria content of the layers increases such that the bottom layer has a lower yttria content than the at least one intermediate layer, and the at least one intermediate layer has a lower yttria content than the top layer.

32. A pre-sintered multi-layer dental mill blank according to claim 30 or 31, wherein the yttria content of the layers increases from the bottom layer to the top layer.

33. The pre-sintered multi-layer dental mill blank according to any one of claims 20 to 32, each layer comprises zirconium oxide and yttrium oxide, wherein the yttrium oxide content of the layers increases from the bottom layer to the top layer, preferably from layer to layer, Each layer contains a sintering activator (e.g., zinc oxide, gallium oxide, or a combination thereof), Optionally, each layer comprises a colored metal oxide, and The base layer, and optionally each of the at least one intermediate layer, comprises a sintering inhibitor (eg, type II yttrium oxide).

34. The pre-sintered multilayer dental mill blank according to any one of claims 27 to 33, wherein the top layer comprises aluminum oxide in an amount of less than 0.05 wt%, or less than 0.02 wt%, or less than 0.01 wt%, based on the total weight of the top layer.

35. The pre-sintered multi-layer dental mill blank according to any one of claims 27 to 34, each layer comprising a sintering activator selected from the group consisting of zinc oxide, gallium oxide, or combinations thereof.

36. The pre-sintered multilayer dental mill blank according to any one of claims 27 to 35, wherein the bottom layer comprises a sintering inhibitor, which is yttrium oxide obtainable by converting a sintering inhibitor precursor, which is a yttrium salt, into the sintering inhibitor during pre-sintering of the green body of the multilayer dental mill blank.

37. The pre-sintered multilayer dental mill blank according to any one of claims 27 to 36, said top layer comprising yttrium oxide in an amount by weight ranging from 9.0 wt.% to 12.0 wt.%, based on the total weight of said top layer, The base layer includes yttrium oxide in an amount ranging from 5.5 wt % to 7.5 wt % based on the total weight of the base layer.

38. The pre-sintered multi-layer dental mill blank according to any one of claims 19 to 37, comprising: a top layer L4, which can be obtained from yttria-stabilized zirconia powder P3, an intermediate layer L3, which may be obtained from a mixture of yttria-stabilized zirconium oxide powders P2 and P3, an intermediate layer L2, which may be obtained from a mixture of yttria-stabilized zirconium oxide powders P1 and P2, a bottom layer L1, which is obtainable from yttria-stabilized zirconia powder P1, and The powder P1 has an yttrium oxide content ranging from 4.5 wt % to 6.1 wt %, the powder P2 has an yttrium oxide content ranging from 6.2 wt % to 7.9 wt %, and the powder P3 has an yttrium oxide content ranging from 8.0 wt % to 11.0 wt %.

39. The pre-sintered multi-layer dental mill blank according to any one of claims 19 to 38, which is pre-colored.

40. A pre-sintered multi-layer dental mill blank according to any one of claims 19 to 39, characterised by providing a representative test cross section of each layer, said representative test cross section being characterised by a fracture toughness K of 0.05 when fully sintered by a rapid sintering process. Ic , and the fracture toughness K of the top layer IC 2.5 to 3.5 MPa*m 1 / 2 , 2.7 to 3.3 MPa*m 1 / 2 or 2.8 to 3.2 MPa*m 1 / 2 The fracture toughness K of the bottom layer is IC 3.6 to 5.5 MPa*m 1 / 2 , 3.8 to 4.8 MPa*m 1 / 2 or 4.0 to 4.6 MPa*m 1 / 2 or 4.0 to 4.4 MPa*m 1 / 2 within the range.

41. The pre-sintered multi-layer dental mill blank according to any one of claims 19 to 40, consisting of: Top floor L4, Middle layer L3, the middle layer L2, and Bottom layer L1, And said layers L4 to L1 comprise the components as defined in Table 1b, wherein the indicated weight amounts are based on the total weight of the corresponding layer: Table Ib: 。 42. The pre-sintered multilayer dental mill blank according to any one of claims 19 to 41, the rapid sintering process being a sintering process having a total duration of less than 25 minutes and having a maximum sintering temperature in the range of 1350°C to 1650°C.

43. The pre-sintered multi-layer dental mill blank according to any one of claims 19 to 42, wherein the rapid sintering method is a sintering method consisting of the following steps: - a first heating step starting from 25 °C at a heating rate of 200 K / min and ending at 1050 °C, - a second heating step starting at 1050 °C and ending at 1450 °C at a heating rate of 100 K / min, - a hold step where the temperature is kept at 1450°C for 2 minutes, - a first cooling step starting from 1450°C and ending at 1350°C at a cooling rate of 130 K / min, - a second cooling step starting from 1350°C and ending at 1200°C at a cooling rate of 70 K / min, followed by cooling, and Wherein the first heating step and the second heating step are performed by applying a vacuum at a pressure in the range of 50 mbar to 100 mbar until a temperature of 1400° C. is reached, and once the temperature of 1400° C. is reached, the vacuum is exchanged with air.

44. A pre-sintered multi-layer dental mill blank comprising the following layers: Top floor L4, Middle layer L3, the middle layer L2, and Bottom layer L1, and said layers L4 to L1 comprise the components as defined in Table 1 herein below, wherein the indicated weight amounts are based on the total weight of the respective layer Table I: 。 45. The pre-sintered multilayer dental mill blank according to any one of claims 1 to 44, one or more of its outer sides being attached to another part or layer, such as a fixing pin, a support layer, a protective layer, a printed layer or a sacrificial layer.

46. ​​A method for preparing a pre-sintered multi-layer dental mill blank, the method comprising the steps of: a) providing three yttria-stabilized zirconium oxide powders P1 to P3, powder P1 having an yttria content in the range of 4.5% to 6.1% by weight, powder P2 having an yttria content in the range of 6.2% to 7.9% by weight, and powder P3 having an yttria content in the range of 8.0% to 11.0% by weight, b) preparing a green body consisting of: The top powder layer of powder P3, at least one intermediate powder layer of a powder mixture chosen from a mixture of powders P2 / P3 and a mixture of powders P1 / P2, a bottom powder layer of powder P1 or a mixture of powders P1 / P2, c) pre-sintering the green body to provide a pre-sintered multi-layer dental mill blank.

47. The method of claim 46, wherein the green body consists of: The top powder layer of powder P3, An intermediate powder layer of a mixture of powders P2 / P3, An intermediate powder layer of a mixture of powders P1 / P2, Bottom powder layer of powder P1.

48. The method according to claim 46 or 47, wherein the mixture of powders P2 / P3 contains powders P2 and P3 in a weight ratio [powder P2:powder P3] in the range of 10:90 to 40:60, in the range of 15:85 to 35:65 or in the range of 20:80 to 30:70, or The mixture of powders P1 / P2 contains powders P1 and P2 in a weight ratio [powder P1:powder P2] within a range of 10:90 to 40:60, within a range of 15:85 to 35:65, or within a range of 20:80 to 30:

70.

49. The method according to any one of claims 46 to 48, comprising adding a sintering activator precursor to the powders P1 to P3 or a mixture thereof, the sintering activator precursor being a zinc salt, a gallium salt or a combination thereof.

50. The method according to any one of claims 46 to 49, comprising adding a sintering inhibitor precursor to the powders P1 and P2 or to a mixture thereof, the sintering inhibitor precursor being a yttrium salt.

51. A method for preparing a dental restoration, the method comprising the steps of: - machining the pre-sintered multilayer dental mill blank according to any one of claims 1 to 45 to provide a dental restoration precursor; - optionally surface treating the dental restoration precursor; - sintering the dental restoration precursor to provide a dental restoration.

52. A dental restoration obtainable by the method for producing a dental restoration according to claim 51.

53. A method for sintering a dental restoration precursor, The method has a total duration of less than 25 minutes and a maximum sintering temperature in the range of 1350° C. to 1650° C., The method comprises subjecting the dental restoration precursor to (i) heat treatment, and (ii) cooling treatment, The cooling process comprises a cooling step A which starts and ends in a temperature range between 1100° C. and the maximum sintering temperature and has a cooling rate A of at least 75 K / min.

54. The method according to claim 53, wherein the cooling step A starts and ends in a temperature range between 1200°C and the maximum sintering temperature and has a cooling rate A of at least 100 K / min.

55. The method according to claim 53 or 54, wherein the cooling process comprises a cooling step B after the cooling step A, the cooling step B having a cooling rate B lower than that of the cooling step A.

56. The method of any one of claims 53 to 55, wherein the heat treatment is carried out in part at a pressure of 500 mbar or less.

57. The method according to any one of claims 54 to 56, The heat treatment comprises a heating step A with a heating rate A of at least 170 K / min, and The heating step A is followed by a heating step B, which has a heating rate B of at least 70 K / min and is lower than the heating rate A.

58. The method of any one of claims 53 to 57, wherein the dental restoration precursor comprises at least three cross-sections, each cross-section comprising zirconium oxide and yttrium oxide, and each cross-section having a different yttrium oxide content.

59. A dental oven configured to carry out the method of any one of claims 53 to 58.

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