Presintered multilayer dental mill blank, process for its preparation, its uses, and sintering process

Abstract

The present invention relates to a pre-sintered multi-layer dental mill blank including a top layer, a bottom layer, and at least one intermediate layer. The pre-sintered multi-layer dental mill blank, or a part prepared therefrom, has one or more desirable properties when fully sintered by a rapid sintering process. The present invention also relates to a process for preparing a dental restoration using the pre-sintered multi-layer dental mill blank, as well as such a dental restoration. The present invention further relates to a process for sintering a dental restoration precursor.

Description

[Technical Field]

[0001] Priority application This application claims priority to U.S. Provisional Patent Application No. 63 / 485,147, filed February 15, 2023, and European Patent Application Publication No. 23156705, filed February 15, 2023. The priority applications are incorporated herein by reference in their entirety for all purposes.

[0002] The present invention relates to a pre-sintered multi-layer dental mill blank and a process for preparing the pre-sintered multi-layer dental mill blank. The present invention also relates to dental restorations obtainable from the pre-sintered multi-layer mill blank. The present invention further relates to a process for sintering a dental restoration precursor. [Background technology]

[0003] 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 several optical characteristics that can be considered common to 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 underlying dentin portion. The upper incisal or occlusal portion is typically more translucent and may be lighter than the underlying dentin portion. The portion of the tooth between these two portions often exhibits some sort of gradual change or transition in color and translucency. In addition to the aesthetics of dental restorations, dental restorations must also possess appropriate mechanical properties and be durable. Preparation of individual dental restorations must be fast and efficient to provide patients at a dental clinic or dental health care center with adequate treatment from start to finish in a short time.

[0004] In modern dentistry, dental restorations are often prepared from ceramic materials, such as zirconia ceramic materials. Ceramic dental restorations are typically prepared from dental ceramic mill blanks. Dental ceramic mill blanks are typically porous and not completely sintered to provide adequate machinability and ease of processing, similar to CAD / CAM processes. Multilayer dental mill blanks, which contain different ceramic materials in different layers from the top to the bottom of the mill blank, are available in the art. These dental mill blanks are used to provide dental restorations with a gradual change in optical appearance from the incisal region to the dentin region of the restoration. 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 does not yet have the final density and therefore the final dimensions. To provide the ceramic dental restoration with its final density and dimensions, the dental restoration precursor must be subjected to a final sintering process. The final properties, such as the optical properties, of the ceramic dental restoration are strongly influenced by the final sintering process. To obtain satisfactory results for dental restorations, it is usually necessary to carry out a relatively long final sintering process, such as a sintering process with an overall sintering time of several hours. Thus, the final sintering accounts for a large portion of the time required to prepare an individualized ceramic dental restoration, significantly increasing the time required to provide the necessary treatment to the patient.

[0005] To reduce the overall time required to prepare a dental restoration, it is desirable to shorten the final sintering process. This is particularly important when aiming for short processing times that enable so-called chairside (as opposed to laboratory) applications, in which a patient can be provided with a final dental restoration in a single visit. However, attempting to significantly shorten the final sintering time using known multilayer dental mill blanks can result in dental restorations with unsatisfactory properties, such as poor optical properties. For example, dental restorations may be obtained with an unnatural appearance, such as those that do not exhibit uniform changes in optical properties across different regions of the restoration.

[0006] There is a continuing need in the art for dental mill blanks suitable for providing dental restoration precursors that can be sintered to full density in the shortest possible time while providing dental restorations with good optical appearance. Summary of the Invention

[0007] One object of the present invention is to at least partially overcome one or more drawbacks of prior art dental mill blanks. One object of the present invention is to provide a dental mill blank that allows for improved patient convenience, such as chairside application, while providing dental restorations with attractive aesthetics. One object of the present invention is to provide a dental mill blank that is suitable for providing dental restorations with desirable properties, such as optical properties. One object of the present invention is 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 dental restorations with desirable properties, such as desirable optical properties, such as a gradual increase in translucency from the dentin region to the incisal region.

[0008] At least one of the above objectives is at least partially solved by embodiments and aspects of the present invention.

[0009] One aspect of the present invention provides a pre-sintered multi-layer dental mill blank including a top layer, a bottom layer, and at least one intermediate layer.

[0010] In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing a representative test section for each layer, which, when fully sintered by a rapid sintering process, has a contrast ratio that increases layer by layer from the top layer to the bottom layer.

[0011] In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing representative test sections for each layer, which, when fully sintered by a rapid sintering process, have CIE L* lightness values ​​that increase layer by layer from the bottom layer to the top layer.

[0012] In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing a representative test section for each layer, wherein the representative test section of the top layer and / or an intermediate layer adjacent to the top layer, when fully sintered by a rapid sintering process, has a number of pores per grain of less than 0.25.

[0013] In one embodiment, each layer of the pre-sintered multilayer dental mill blank comprises zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer, and the top layer comprises a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof).

[0014] In one embodiment, each layer of the pre-sintered multilayer dental mill blank comprises zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer, and the top layer comprises aluminum oxide in an amount of less than 0.01 wt%, based on the total weight of the top layer.

[0015] One aspect of the present invention provides a process for preparing a presintered multi-layer dental mill blank, the process comprising: a) providing three yttria-stabilized zirconia powders P1 to P3, where P1 has an yttria content in the range of 4.5 to 6.1 wt%, P2 has an yttria content in the range of 6.2 to 7.9 wt%, and P3 has an yttria content in the range of 8.0 to 11.0 wt%; b) preparing a green body, The top powder layer of powder P3, at least one intermediate powder layer of a powder mixture selected from the mixture of powders P2 / P3 and the mixture of powders P1 / P2, preparing a green body, the green body being composed of 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.

[0016] Another aspect of the present invention provides a process for preparing a dental restoration, the process comprising the steps of machining a pre-sintered multilayer 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 precursor to provide the dental restoration.

[0017] Another aspect of the present invention provides a dental restoration, which is obtainable by a process for preparing a dental restoration according to any one of the embodiments of the present invention.

[0018] Yet another aspect of the present invention provides a process for sintering a dental restoration precursor, the process having a total sintering time of less than 25 minutes and a maximum sintering temperature in the range of 1350°C to 1650°C; The process comprises: (i) heat treatment; (ii) a cooling treatment, The cooling treatment comprises a cooling step A, which starts and ends within a temperature range between 1100° C. and the maximum sintering temperature, and has a cooling rate A of at least 75 K / min.

[0019] definition Within the context of the present invention, the following terms have the following meanings:

[0020] As used herein, "sintering" means densifying a porous ceramic material into a denser, less porous material by subjecting it to heating at a temperature suitable for densification, which temperature is below the melting point of the major component of the ceramic material.

[0021] As used herein, "pre-sintered" or "pre-sintering" refers to subjecting a ceramic green body to heating to partially or completely remove or decompose organic binders, inorganic binders, or thermally unstable components. Pre-sintering generally results in at least partial formation of sintering necks at interconnected grain boundaries in the ceramic material and thermal hardening of the ceramic material, which may promote the material's workability or machinability. The relative densification from the ceramic green body to the pre-sintered ceramic material is typically 5% or less relative to the dimensions of the ceramic green body. Pre-sintered ceramic materials usually have an open porous structure that can be further densified when the material is fully sintered in a subsequent sintering step. The density of pre-sintered ceramic materials, such as pre-sintered zirconia ceramics, can range from 45 to 70% of the theoretical density of the ceramic material. For zirconia ceramic materials, pre-sintering is typically performed at temperatures of up to 700°C to 1200°C. The temperature at which the ceramic body is pre-sintered can be determined by one skilled in the art by measuring thermal expansion using, for example, a dilatometer.

[0022] As used herein, "fully sintered" or "fully sintering" means that the ceramic material has been sintered to a density of at least 98.5%, such as at least 99.5% or at least 99.8%, of the ceramic material's theoretical density. The density of a material can be determined by the Archimedes method according to DIN EN 623-2 or by weighing the material and geometrically determining its volume. The theoretical density of a fully sintered material can be determined by one skilled in the art, for example, based on the material's components. Additionally or alternatively, the theoretical density of a ceramic material can be determined by grinding the ceramic material into a powder having a volumetric median particle size in the range of 10 to 30 μm, e.g., 20 μm, and determining the density of the powder using a pycnometer. The volumetric median particle size can be determined by laser diffraction, for example, according to ISO 13320 (2009). The layers of a multilayer dental mill blank can have different theoretical densities depending on the ceramic material present in each layer. In such cases, the density and theoretical density of the ceramic material can also be determined individually for each layer.

[0023] A "green body" is a compact of ceramic powder that has not been subjected to a sintering or presintering step and typically contains organic binders, inorganic binders, or other additives. Compacts are typically prepared by compacting (e.g., pressing) the ceramic powder.

[0024] As used herein, "porous" means that a material has pores, and is intended to include both open-porous and closed-porous materials. An "open-porous" material is a material having pores that are at least partially interconnected and at least partially accessible from the outside, e.g., by gas or liquid flow. An open-porous material as defined herein may also have pores that are not accessible from the outside, e.g., by gas or liquid flow. A "closed-porous" material is a material that is not open-porous but has closed pores, i.e., pores that are not accessible from the outside, e.g., by gas or liquid flow. "Porosity" is a measure of pore-like voids in a solid material, and is the ratio of the volume of voids to the total volume of the solid material. The ratio may be expressed as a percentage from 0 to 100%.

[0025] "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.

[0026] "Dental mill blank" means a solid, geometrically defined, three-dimensional object of material, such as a block or disc, from which dental articles can be machined, e.g., by cutting, milling, grinding, drilling, etc.

[0027] As used herein, "dental restoration" refers to an article useful in the fields of dentistry or orthodontics to restore, modify, support, and / or reconstruct a tooth or portion thereof, or a group of teeth or portions thereof. A dental restoration may 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.

[0028] As used herein, "dental restoration precursor" refers to a workpiece machined from a dental mill blank that already has the shape of a dental restoration, but has not yet been fully sintered and therefore does not yet have its final dimensions.

[0029] "Layer" refers to an individual layer of a presintered multilayer dental mill blank that has one or more, typically multiple, properties that are substantially homogeneous within the dimensions of the layer. The one or more properties may be optical properties (e.g., CIE L*a*b* values ​​or contrast ratios determined as described herein) and / or amounts of one or more base components (e.g., zirconia and / or yttria) when fully sintered. In this context, "substantially homogeneous" should be understood to have substantially the same value or property within the layer regardless of measurement location, subject to tolerances due to unavoidable manufacturing variations and / or measurement deviations, as described herein.

[0030] As used herein, "contrast ratio" refers to the ratio of the illuminance (Y) of a material when placed on a black background (Yb) to the illuminance of the same material when placed on a white background (Yw) (CR = Yb / Yw). The contrast ratio can be determined in accordance with BS5612, particularly BS5612:1978. A suitable device for measuring the contrast ratio is, for example, the spectrophotometer CM3700-D (Konica-Minolta). The 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 transmitted light intensity to incident light intensity. A contrast ratio close to 0% can indicate that a given material is almost completely transparent, while a contrast ratio of 100% can indicate that the material is completely opaque.

[0031] CIE (Commission Internationale de l'Eclairage, International Commission on Illumination) L*a*b* (CIELAB) values ​​are used herein to characterize the color of a material in a three-dimensional color space. The L* of an individual color is a measure of luminance and lightness, which is represented on the vertical axis of the color space. The a* and b* coordinates are measures of chromaticity, which are represented on the horizontal axis of the color space, with positive a* representing red, negative a* representing green, positive b* representing yellow, and negative b* representing blue. CIE L*a*b* values ​​can be measured according to DIN 6174. A suitable device for measuring contrast ratio is, for example, the spectrophotometer CM3700-D (Konica-Minolta).

[0032] 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 the incisal or occlusal zone in a dental restoration obtained from the mill blank by machining and sintering.

[0033] "Intermediate layer" means a layer located between the top and bottom layers of a presintered multilayer dental mill blank. At least one intermediate layer can be used to prepare at least a portion of the transition zone of a dental restoration obtained from the mill blank by machining and sintering.

[0034] "Bottom layer" means the outermost layer of a multilayer dental mill blank that is located on the opposite side of the multilayer dental mill blank from the top layer. The bottom layer can be used to prepare at least a portion of the dentin zone of a dental restoration obtained from the mill blank by machining and sintering.

[0035] The terms "top layer," "intermediate layer," and "bottom layer" should not be construed as requiring the multilayer dental mill blank to be arranged in a particular manner or orientation. Furthermore, other parts or layers that are additionally present on the exterior of the multilayer dental mill blank (e.g., a support layer, a protective layer, a printing layer, or a sacrificial layer) and that are not intended to become part of a dental article machined from the multilayer dental mill blank are not to be understood as the top, intermediate, or bottom layer of the pre-sintered multilayer dental mill blank or as part of the dental mill blank. In one embodiment, the pre-sintered multilayer dental mill blank is attached to another part or layer, such as, but not limited to, a retaining pin, a support layer, a protective layer, a printing layer, or a sacrificial layer, on one or more of its exteriors (e.g., all of its exteriors). A sacrificial layer can be, for example, a thin ceramic layer that is removed when machining a dental article from the pre-sintered multilayer dental mill blank.

[0036] As used herein, a "rapid sintering process" refers to a sintering process for preparing a fully sintered ceramic material from a ceramic material precursor, wherein the total sintering time is less than 45 minutes.

[0037] As defined herein, a "sintering process" refers to 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. This contrasts with, for example, a "cool-down," which is uncontrolled and does not involve active adjustment of the cooling rate. The above sequence is typically programmed into the sintering furnace before the sintering process begins. As defined herein, a "cool-down" is not part of the sintering process. A "cool-down" refers to a cooling phase that begins after the final controlled temperature adjustment step (e.g., a final controlled cooling step) is completed. A cool-down can occur, at least in part, in an open sintering furnace. A cool-down typically takes several minutes (e.g., 2 to 8 minutes). A cool-down is typically considered complete at temperatures ranging from 300°C to 400°C. Of course, a cool-down can also occur at temperatures as low as room temperature. As defined herein, the "total sintering time" of a sintering process refers to the time elapsed during all controlled temperature regulation steps of the sintering process, i.e., including all controlled heating, holding, and cooling steps, but excluding the cool-down. As used herein, "room temperature" refers to a temperature within the range of 15°C to 50°C.

[0038] Unless explicitly stated otherwise, the "yttria content" or "amount of yttria" (both expressions are used interchangeably herein) of an item, such as a powder, composition, layer, or mill blank, refers to the total amount of yttria present in the item, regardless of how the yttria was introduced into the item. As defined herein, the yttria content may include type I yttria and type II yttria. As defined herein, "type I yttria" or "type I yttria content" refers to the yttria or yttria content present in the yttria-stabilized zirconia powder used to prepare at least a portion of the powder layers of the green body from which the presintered multilayer dental mill blank is obtained by presintering. Thus, when the yttria content of an yttria-stabilized zirconia powder is described herein, the yttria content is typically the type I yttria content. As defined herein, "type II yttria" or "type II yttria content" refers to yttria obtained by converting yttrium salt to yttria during pre-sintering of the green body of a multilayer dental mill blank. For example, the surfaces of particles in a powder granulation may be treated with yttrium salt. The surface-treated powder granulation may then be used to prepare the powder layer of a green body, and the yttrium salt may be at least partially located on the boundaries between different particles. When the green body is pre-sintered, the yttrium salt is converted to type II yttria. Type II yttria may segregate to grain boundaries during and / or after pre-sintering.

[0039] "Yttria-stabilized zirconia" means zirconia that exists at least partially in the tetragonal or cubic phase and that has incorporated into its crystal lattice a sufficient amount of yttria to at least partially prevent the tetragonal and cubic phases, respectively, from transforming to the monoclinic phase during cooling to room temperature. At room temperature, pure zirconia exists in the monoclinic phase, which is its most stable crystalline phase. As the temperature of zirconia increases to about 1170°C, the monoclinic phase transforms to the tetragonal phase, which then transforms to the cubic phase at about 2370°C. By incorporating an appropriate amount of yttria into the crystal lattice of zirconia, the tetragonal or cubic phase of zirconia is at least partially stabilized, i.e., the tetragonal and cubic phases, respectively, are at least partially prevented from transforming to the more stable (room temperature) monoclinic phase of zirconia. Depending on the amount of yttria incorporated into the zirconia crystal lattice, yttria-stabilized zirconia can be provided in its tetragonal phase, in the form of a mixture of the tetragonal phase and the cubic phase, or in the form of its cubic phase. For example, yttria-stabilized zirconia containing about 3 mol% yttria can be provided in its tetragonal phase without the presence of a substantial amount of cubic phase. Yttria-stabilized zirconia containing about 4 mol% or 5 mol% yttria can be provided in the form of a mixture of the tetragonal and cubic phases. Yttria-stabilized zirconia containing about 8 mol% or more yttria can be provided in its cubic phase.

[0040] As used herein, a "sintering accelerator" is a metal oxide that is added to a ceramic material (e.g., yttria-stabilized zirconia) to shift the temperature required to achieve a specific densification in the (final) sintering process of the ceramic material to a lower temperature range. The sintering accelerator may be added to the ceramic material in the form of a sintering accelerator precursor. As used herein, a "sintering accelerator precursor" refers to a metal salt that can be converted to an oxide of the metal in a heating step, e.g., a pre-sintering step, to provide the sintering accelerator metal oxide.

[0041] As used herein, a "sintering inhibitor" is a metal oxide that is added to a ceramic material (e.g., yttria-stabilized zirconia) to shift 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 may 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 an oxide of the metal in a heating step, e.g., a pre-sintering step, to provide the metal oxide that is the sintering inhibitor.

[0042] A "pre-shaded" multi-layer dental mill blank means a multi-layer dental mill blank that includes colored metal oxides in an amount and / or combination effective to impart color (e.g., a color that matches the natural color of the teeth and / or a color that matches the color of the teeth according to the VITA classical A1-D4® shade guide using VITA Bleached Shades, manufactured by Vita Zahnfabrik, or a similar dental shade guide system) to a dental restoration (or at least a portion thereof) that is machined from the mill blank and then fully sintered.

[0043] When the term "comprising" is used herein, it does not exclude the presence of additional, unspecified elements. When the term "essentially consisting of" is used herein, it does not exclude the presence of other, unspecified elements that do not materially affect the essential properties of the defined subject matter. When the term "consisting of" is used herein, it excludes the presence of additional, unspecified elements. However, it does not exclude the presence of unavoidable components, such as unavoidable trace impurities (e.g., SiO2, CaO, TiO2, or Na2O) totaling less than 0.1 wt% when a composition is defined. For purposes of the present invention, the terms "essentially consisting of" and "consisting of" are considered to be specific embodiments of the term "comprising of." Whenever the terms "including" or "having" are used, these terms are intended to be equivalent to "comprising" as defined above.

[0044] The term "obtained" does not necessarily mean, for example, that an embodiment must be obtained by the sequence of steps that follow the term "obtained," even though such a restrictive understanding is always included by the term "obtained" as a preferred embodiment.

[0045] When a layer is described herein as including, having, or being a weight content of a component, the weight content of the component is based on the total weight of its respective layer (unless expressly stated otherwise). Furthermore, when a pre-sintered multilayer dental mill blank is described herein as including, having, or being a weight content of a component, the weight content of the component is based on the total weight of the pre-sintered multilayer dental mill blank (unless expressly stated otherwise). Furthermore, when a pre-sintered multilayer dental mill blank or one of its layers is described herein as including a specific weight of a metal or metal cation, and the metal or metal cation is not defined as a metal oxide, it will be understood that the weight of the metal or metal cation is calculated based on the (most abundant) oxide of that metal or metal cation.

[0046] Numerical values ​​defined herein are meant to be rounded to the nearest digit and encompass a range 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, etc. [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 10 is a graphical representation of the contrast ratio values ​​of layers L1 through L4 provided in Tables 8A and 8B in the Examples section. [Figure 2] FIG. 1 is a graphical representation of the CIE L* values ​​of layers L1 through L4 provided in Tables 8A and 8B of the Examples section. [Figure 3] 1 shows a test cross-sectional section of a dental mill blank according to mill blank number 7 fully sintered by a rapid sintering process according to Table 5 on the left, and a test cross-sectional section of a dental mill blank according to a comparative example fully sintered by a rapid sintering process according to Table 5 on the right. The top layer L4 of each cross-sectional section is located at the top of the image, and the bottom layer L1 is located at the bottom of the image. [Figure 4]FIG. 4 shows an overview of the microstructure of the intermediate layer L3 of the fully sintered test cross-sectional section of mill blank number 7 shown in FIG. 3. [Figure 5] FIG. 5 shows a portion of the surface of FIG. 4 at a higher magnification. [Figure 6] FIG. 4 shows a region of interest (ROI) selected from a portion of the surface of the top layer L4 of a fully sintered test cross-sectional section of mill blank number 7 shown in FIG. 3. [Figure 7] FIG. 4 shows an overview of the microstructure of the intermediate layer L3 of a fully sintered test cross-sectional section of the comparative mill blank shown in FIG. 3. [Figure 8] FIG. 8 shows a portion of the surface of FIG. 7 at a higher magnification. [Figure 9] FIG. 4 shows a region of interest (ROI) selected from a portion of the surface of the top layer L4 of a fully sintered test cross-sectional section of the comparative mill blank shown in FIG. 3. [Figure 10] FIG. 1 shows the sintering curve of an untreated 5 mol% yttria-stabilized zirconia material (right-most curve, "Undoped") compared to the sintering curves of 5 mol% yttria-stabilized zirconia materials containing different weight amounts of zinc oxide or gallium oxide as a sintering promoter. [Figure 11] FIG. 1 shows a comparison of the sintering curves of an untreated 3 mol% yttria-stabilized zirconia material (right curve "3Y"), a 3 mol% yttria-stabilized zirconia material containing a colorant and zinc oxide as a sintering aid (left curve "colored and doped with ZnO"), and a 3 mol% yttria-stabilized zirconia material containing a colorant, zinc oxide as a sintering aid, and type II yttria as a sintering inhibitor (middle curve "colored and doped with ZnO / YO"). [Figure 12]FIG. 12 shows the sintering curves of an untreated 3 mol% yttria-stabilized zirconia material (left dashed line "Undoped 3Y"), an untreated 4 mol% yttria-stabilized zirconia material (middle dashed line "Undoped 4Y"), and an untreated 5 mol% yttria-stabilized zirconia material (right dashed line "Undoped 5Y"). The sintering curves are compared with those of a material containing a colorant (A3.5 shade), zinc oxide as a sintering accelerator, and optionally type II yttria as a sintering inhibitor. FIG. 12 shows the sintering kinetics adjustment after doping with sintering accelerators and inhibitors, e.g., by a shift to lower temperatures in the sintering curves. DETAILED DESCRIPTION OF THE INVENTION

[0048] I. Pre-sintered multilayer dental mill blanks 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 may be further defined by its composition, its morphology, structure, and / or layers, by the properties of a representative test section sintered by a rapid sintering process.

[0049] 1. Properties of a representative test section when fully sintered by the rapid sintering process Pre-sintered multi-layer dental mill blanks according to the present invention can be characterized by providing representative test sections for each layer, which when fully sintered by a rapid sintering process can have specific properties such as contrast ratio, CIE L*a*b* values, porosity, and / or mechanical properties.

[0050] 1.1 Representative test section Presintered multilayer dental mill blanks according to the present invention can be characterized by providing representative test sections for each layer, which can be fully sintered by a rapid sintering process to provide fully sintered representative test sections having one or more particular properties. The fully sintered representative test sections can be obtained by preparing representative test sections for each layer from the presintered multilayer dental mill blank by a subtractive process (e.g., cutting, milling, sawing), and then fully sintering the representative test sections by a rapid sintering process.

[0051] There are various options for preparing representative test sections for each layer. Representative test sections can be cut (e.g., using a precision saw) from each one of the layers of the pre-sintered multilayer dental mill blank. For example, the representative test sections can be cut substantially parallel to adjacent layers and have a substantially planar shape. Representative test sections cut separately for each layer in this manner can be used when determining the contrast ratios and / or CIE L*a*b* values ​​described herein. Accordingly, in certain embodiments of the present invention, the pre-sintered multilayer dental mill blank is characterized by providing a representative test section for each layer, each one of the representative test sections being prepared (e.g., cut) from a respective 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 by providing a representative test section for each layer, each one of the representative test sections being cut from a respective one of the layers of the pre-sintered multilayer dental mill blank, each one of the representative test sections having a substantially planar shape and being substantially parallel to the adjacent layers.

[0052] Instead of cutting out 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-sectional section from a pre-sintered multilayer dental mill blank containing all layers. The representative test section for each layer in the form of a cross-sectional section can be used to determine the number of pores per grain, as described herein. Therefore, in certain embodiments of the present invention, a pre-sintered multilayer dental mill blank is characterized by providing a representative test section for each layer, the representative test section being prepared (e.g., cut) in the form of a cross-sectional section of a pre-sintered multilayer dental mill blank containing all layers. Therefore, in certain embodiments of the present invention, a pre-sintered multilayer dental mill blank is characterized by providing a representative test section for each layer, the representative test section being prepared (e.g., cut) in the form of a cross-sectional section of a pre-sintered multilayer dental mill blank containing all layers, the cross-sectional section having a substantially planar shape and cut substantially perpendicular to the outer surface of the top layer.

[0053] The representative section may be prepared from a portion of the pre-sintered dental mill blank that is at least 1 mm from the outer surface of the pre-sintered dental mill blank. This may ensure that the representative test section is free of defects that may necessarily be present on or near the surface of the mill blank. The representative test section may be processed, such as ground and / or polished, before being subjected to full sintering via a rapid sintering process. The fully sintered representative test section may be processed to a specific thickness, such as polished and / or surface polished, before being subjected to a measurement method.

[0054] In this specification, even if a specific thickness (e.g., 0.8 mm) is specified for measuring a characteristic of a fully sintered representative test section (e.g., contrast ratio or CIE L*a*b* values), this should not be interpreted as meaning that each layer of a pre-sintered dental mill blank must necessarily have that specific thickness as a minimum thickness (although this is possible). If a layer of a pre-sintered multilayer dental mill blank is not thick enough to prepare a fully sintered representative test section having a specific thickness (e.g., 0.8 mm), a fully sintered representative test section of that layer can be prepared from an equivalent pre-sintered multilayer dental mill blank having layers of the same composition and sufficient thickness. Similarly, even if a specific measurement method, such as a standardized measurement method (e.g., ISO or ASTM standard), is followed to measure a characteristic of a fully sintered representative test section (e.g., flexural strength or fracture toughness), this should not be interpreted as meaning that each layer of a pre-sintered dental mill blank must necessarily have the test specimen dimensions necessary to perform that specific measurement method (although this is possible). If a layer of a pre-sintered multi-layer dental mill blank does not have sufficient specimen dimensions to perform a particular measurement method, a fully sintered representative test section of that layer can be prepared from an equivalent pre-sintered multi-layer dental mill blank having layers of the same composition and sufficient dimensions.

[0055] 1.2 Rapid sintering process As defined herein, a rapid sintering process may be a sintering process having a total sintering time of less than 25 minutes or less than 20 minutes (e.g., 14, 15, or 16 minutes), such as in the range of 12 to 25 minutes or 12 to 20 minutes, and a maximum sintering temperature in the range of at least 1350°C, at least 1400°C, up to 1650°C, or up to 1600°C, or up to 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, a rapid sintering process is a sintering process having a total sintering time of less than 20 minutes and a maximum sintering temperature in the range of 1400°C to 1500°C. For example, a rapid sintering process may be a sintering process having a total sintering time in the range of 12 to 20 minutes and a maximum sintering temperature of 1450°C. A suitable sintering furnace for carrying out such a sintering process is the Programat CS6 sintering furnace, which is commercially available from Ivoclar Vivadent AG.

[0056] The rapid sintering process as defined herein comprises the following steps: a first heating step starting at -25°C and ending at 1050°C with a heating rate of 200 K / min; a second heating step starting at -1050°C and ending at 1450°C with a heating rate of 100 K / min; a holding step at -1450°C for 2 minutes; a first cooling step starting at -1450°C and ending at 1350°C with a cooling rate of 130 K / min; a second cooling step starting at -1350°C and ending at 1200°C with a cooling rate of 70 K / min, which is followed by a cool down; and The first and second heating steps are carried out at a pressure in the range of 50 mbar to 100 mbar (e.g., 80 mbar) by applying a vacuum until a temperature of 1400°C is reached, at which point the vacuum is replaced with air.

[0057] A rapid sintering process, as defined herein, can be a sintering process described in Table 5. A cool-down, which is not considered part of the sintering process, may be completed in less than 10 minutes, less than 5 minutes, or less than 3 minutes (e.g., when a temperature of 400°C is reached).

[0058] 1.3 contrast ratio One embodiment of the present invention is a pre-sintered multi-layer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; The pre-sintered multi-layer dental mill blank is characterized by providing a representative test section for each layer, which, when fully sintered by a rapid sintering process, provides a pre-sintered multi-layer dental mill blank having a contrast ratio that increases from the top layer to the bottom layer.

[0059] The contrast ratio can increase from the top layer to the bottom layer, such that the contrast ratio of the top layer is lower than the contrast ratio of at least one intermediate layer, and the contrast ratio of at least one intermediate layer is lower than the contrast ratio of the bottom layer. In one embodiment, the pre-sintered multi-layer dental mill blank includes multiple intermediate layers, and the contrast ratio does not increase from layer to layer for each intermediate layer in the direction from the top layer to the bottom layer. However, it is preferred that the contrast ratio of each layer increases from layer to layer from the top layer to the bottom layer.

[0060] One embodiment of the present invention is a pre-sintered multi-layer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; The pre-sintered multi-layer dental mill blank is characterized by providing a representative test section for each layer, which, when fully sintered by a rapid sintering process, provides a pre-sintered multi-layer dental mill blank having a contrast ratio that increases layer by layer from the top layer to the bottom layer.

[0061] As described herein, when the contrast ratio increases from layer to layer, the pre-sintered multi-layer dental mill blank is suitable for preparing dental restorations with a natural and highly aesthetic appearance by a rapid sintering process. For example, the mill blank can be used to prepare a dental restoration with increasing translucency from its bottom portion (e.g., a portion of the dentin zone of the restoration) over a transitional portion to its top portion (e.g., a portion of the incisal zone of the restoration) by a rapid sintering step.

[0062] The representative test sections are fully sintered by a rapid sintering process to obtain fully sintered representative test sections, each having a specific contrast ratio. The contrast ratio preferably increases layer by layer from the fully sintered representative test section of the top layer to the fully sintered representative test section of the bottom layer. For example, when a pre-sintered multi-layer dental mill blank is composed of a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1, the contrast ratio preferably increases layer by layer from the fully sintered representative test section of the top layer L4 to the fully sintered representative test section of the intermediate layer L3 to the fully sintered representative test section of the intermediate layer L2 to the fully sintered representative test section of the bottom layer L1.

[0063] Unless otherwise specified, contrast ratios defined herein refer to the contrast ratio of a representative test section that has been fully sintered by a rapid sintering process. The contrast ratio may be subject to tolerances due to unavoidable manufacturing variations and / or measurement deviations, and is no greater than about ±1.0%.

[0064] The contrast ratio of a fully sintered representative test section typically depends on the thickness of the fully sintered representative test section, with the contrast ratio increasing as the thickness increases. Therefore, the contrast ratio of a fully sintered representative test section is determined relative to a test section having the same or substantially the same thickness. Unless otherwise specified, the contrast ratio defined herein preferably refers to the contrast ratio determined relative to a fully sintered representative test section having a thickness of 0.8 mm, particularly 0.80±0.02 mm. The contrast ratio may be determined in accordance with BS5612, particularly BS5612:1978. A suitable device for measuring the contrast ratio is, for example, the spectrophotometer CM3700-D (Konica-Minolta).

[0065] 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 up to 88%, up to 83%, up to 82%, or up to 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%.

[0066] The contrast ratios of the layers may differ by a particular number of percentage points. 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, for example, in the range of 5 to 19 percentage points.

[0067] The contrast ratio of the top layer and the contrast ratio of the bottom layer can satisfy the following formula (I), (II), (III) or (IV): CR(TL) / CR(BL) ≥ 75.0% (I), CR(TL) / CR(BL) ≥ 77.0% (II), CR(TL) / CR(BL) ≥ 82.0% (III), CR(TL) / CR(BL) ≥ 85.0% (IV), In the formula, CR(TL) is the contrast ratio of the top layer [%], and CR(BL) is the contrast ratio of the top layer [%].

[0068] The contrast ratio of the bottom layer may be at least 66%, at least 70%, at least 71%, or at least 74%. The contrast ratio of the bottom layer may be up to 88%, up to 83%, up to 81%, or up to 80%. The contrast ratio of the bottom layer may be in the range of 66-88%, 70-83%, 71-81%, or 74-80%. In one embodiment, the contrast ratio of the bottom layer is in the range of 70-83%.

[0069] The contrast ratio of the top layer may be at least 56%, at least 61%, at least 62%, or at least 64%. The contrast ratio of the top layer may be up to 72%, up to 68%, up to 67%, or up to 66%. The contrast ratio of the top layer may be in the range of 56-72%, 61-68%, 62-67%, or 64-66%. In one embodiment, the contrast ratio of the top layer is in the range of 61-68%.

[0070] 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 up to 83%, up to 79%, up to 78%, or up to 76%. The contrast ratio of the at least one intermediate layer may be in the range of 62-83%, 66-79%, 67-78%, or 68-76%.

[0071] The contrast ratio [%] of each pair of two 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 two 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 two adjacent layers may differ in the range of 0.3 to 7.0 percentage points, 0.5 to 7.0 percentage points, 1.0 to 7.0 percentage points, 1.5 to 7.0 percentage points, 2.0 to 6.0 percentage points, 2.5 to 6.0 percentage points, or 3.0 to 6.0 percentage points. In one embodiment, the contrast ratio [%] of each pair of two adjacent layers differs by at least 2.0 percentage points, such as in the range of 2.0 to 6.0 percentage points.

[0072] The contrast ratio of the intermediate layer adjacent to the top layer may be at least 62%, at least 66%, or at least 67%. The contrast ratio of the intermediate layer adjacent to the top layer may be up to 74%, up to 72%, up to 71%, or up to 70%. The contrast ratio of the intermediate layer adjacent to the top layer may be in the range of 63-74%, 66-72%, 67-71%, or 67-70%. The contrast ratio [%] of the intermediate layer adjacent to the top layer may differ from the contrast ratio of the top layer by 0.2-9.0 percentage points, 0.5-7.0 percentage points, 1.0-6.0 percentage points, or 1.5-5.0 percentage points.

[0073] The contrast ratio of the intermediate layer adjacent to the bottom layer may 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 may be up to 82%, up to 79%, up to 78%, or up to 77%. The contrast ratio of the intermediate layer adjacent to the bottom layer may be in the range of 64-82%, 68-79%, 69-78%, or 70-77%. The contrast ratio [%] of the intermediate layer adjacent to the bottom layer may differ from the contrast ratio of the bottom layer by 0.5-12.0 percentage points, 1.5-7.0 percentage points, 2.0-5.5 percentage points, or 3.0-4.5 percentage points.

[0074] The pre-sintered multi-layer dental mill blank can include at least two intermediate layers, where the contrast ratio [%] of one intermediate layer can differ from the contrast ratio 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 by up to 12 percentage points, up to 10.0 percentage points, up to 9.0 percentage points, or up to 8.0 percentage points. The pre-sintered multi-layer dental mill blank can include at least two intermediate layers, where the contrast ratio [%] of one intermediate layer can differ from the contrast ratio of the other intermediate layer by 0.2 to 12 percentage points, 0.5 to 10.0 percentage points, 3.0 to 9.0 percentage points, or 4.0 to 8.0 percentage points.

[0075] The presintered multilayer dental mill blank may include the following layers: top layer L4, middle layer L3, middle layer L2, and bottom layer L1, where the contrast ratios of the layers satisfy one or more of the contrast ratio profiles A1.1-J1.1 defined in Table A1 herein. A set of such contrast ratio profiles A1.1-J1.1 (or A1.2-J1.2) is advantageous in that it provides a suitable selection of aesthetic appearances that match the appearance of natural teeth, e.g., in terms of translucency, for most patients. A set of contrast ratio profiles C1.1-H1.1 (or C1.2-H1.2), e.g., F1.1 or G1.1 (or F1.2 or G1.2), is considered particularly advantageous in that it provides a suitable selection of aesthetic appearances that match the appearance of natural teeth, e.g., in terms of translucency, for a large subgroup of all patients.

[0076] [Table 1]

[0077] The pre-sintered multilayer dental mill blank may include the following layers: top layer L4, middle layer L3, middle layer L2, bottom layer L1, where the contrast ratios of the layers satisfy one or more of the contrast ratio profiles A1.2 to J1.2 defined in Table A2 herein.

[0078] [Table 2]

[0079] In one embodiment, the pre-sintered multi-layer dental mill blank is comprised of the following layers: top layer L4, middle layer L3, middle layer L2, and bottom layer L1, with contrast ratios of the layers satisfying one or more of contrast ratio profiles A1.1-J1.1 as defined in Table A1 herein or contrast ratio profiles A1.2-J1.2 as defined in Table A2 herein. In one embodiment, the pre-sintered multi-layer dental mill blank is comprised of the following layers: top layer L4, middle layer L3, middle layer L2, and bottom layer L1, with contrast ratios of the layers satisfying one or more of contrast ratio profiles C1.1-H1.1 as defined in Table A1 herein (e.g., profiles F1.1 or G1.1), or contrast ratio profiles C1.2-H1.2 as defined in Table A2 herein (e.g., F1.2 or G1.2).

[0080] In addition to or instead of the contrast ratios described herein, the representative test sections, when fully sintered by a rapid sintering process, may have further properties, such as CIE L*a*b* values, number of pores per grain, or mechanical properties, as described herein.

[0081] 1.4 CIE L*a*b* values One embodiment of the present invention is a pre-sintered multi-layer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; The pre-sintered multi-layer dental mill blank is characterized by providing representative test sections for each layer, which, when fully sintered by a rapid sintering process, provide a pre-sintered multi-layer dental mill blank having a CIE L* lightness that increases from the bottom layer to the top layer.

[0082] The CIE L* color value can increase from the bottom layer to the top layer such that the CIE L* color value of the bottom layer is lower than the CIE L* color value of at least one intermediate layer, and the CIE L* color value of at least one intermediate layer is lower than the CIE L* color value of the bottom layer. In one embodiment, the pre-sintered multi-layer dental mill blank includes multiple intermediate layers, and the CIE L* color value does not increase from layer to layer for each intermediate layer in the direction from the bottom layer to the top layer. However, it is preferred that the CIE L* color value of each layer increases from layer to layer from the bottom layer to the top layer.

[0083] One embodiment of the present invention is a pre-sintered multi-layer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; The pre-sintered multi-layer dental mill blank is characterized by providing a representative test section for each layer, which, when fully sintered by a rapid sintering process, provides a pre-sintered multi-layer dental mill blank having a CIE L* lightness that increases layer by layer from the bottom layer to the top layer.

[0084] As described herein, when the CIE L* lightness increases with each layer, the pre-sintered multi-layer dental mill blank is suitable for preparing, by a rapid sintering process, dental restorations having desirable optical properties, such as a natural and aesthetic appearance. For example, the mill blank may be suitable for preparing, by a rapid sintering step, dental restorations having a more uniform color transition from its bottom portion (e.g., a portion of the dentin zone of the restoration) over the transitional portion to its top portion (e.g., a portion of the incisal zone of the restoration).

[0085] The representative test sections are fully sintered by a rapid sintering process to obtain fully sintered representative test sections, each having a CIE L*a*b* value. The CIE L* lightness preferably increases layer by layer from the fully sintered representative test section of the bottom layer to the fully sintered representative test section of the top layer. For example, if a pre-sintered multi-layer dental mill blank is composed of a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1, the CIE L* lightness 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 to the fully sintered representative test section of the top layer L4.

[0086] Unless otherwise specified, the CIE L*a*b* values ​​defined herein refer to the CIE L*a*b* values ​​of a representative test section that has been fully sintered by a rapid sintering process. The CIE L* lightness values ​​(and optionally the CIE a* and b* values) may be subject to a tolerance due to unavoidable manufacturing variations and / or measurement deviations, which is approximately ±0.5.

[0087] The CIE L*a*b* values ​​of a fully sintered representative test section typically depend on its thickness. Therefore, the CIE L*a*b* values ​​of a fully sintered representative test section are determined relative to a test section having the same or substantially the same thickness. Unless otherwise specified, the CIE L*a*b* values ​​defined herein preferably refer to CIE L*a*b* values ​​determined relative to a fully sintered representative test section having a thickness of 0.8 mm, particularly 0.80±0.02 mm. The CIE L*a*b* values ​​may be measured according to DIN 6174. Measurements can be performed using a spectrophotometer CM3700-D (Konica-Minolta). Measurements can be performed against a background of, for example, L*=93.1, a*=(-0.64), and b*=4.22.

[0088] The CIE L* lightness of each layer may be at least 72, at least 76, at least 78, or at least 79. The CIE L* lightness of each layer may be up to 98, up to 94, up to 92, or up to 91. The CIE L* lightness of each layer may range from 72 to 98, 76 to 94, 78 to 92, or 79 to 91. In one embodiment, the CIE L* lightness of each layer is in the range of 78 to 92.

[0089] The CIE L* lightness 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 L* lightness 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 L* lightness of each pair of two adjacent layers may differ by a value ranging from 0.05 to 3.0, from 0.4 to 3.0, from 0.6 to 2.5, or from 0.8 to 2.0. In one embodiment, the CIE L* lightness 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.

[0090] The CIE L* lightness 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 L* lightness of the bottom layer may be up to 94, up to 92, up to 90, up to 88, up to 86, or up to 84. The CIE L* lightness of the bottom layer may be in the range of 72-94, 76-92, 78-90, 80-88, or 80-86. In one embodiment, the CIE L* lightness of the bottom layer is in the range of 76-92.

[0091] The CIE L* lightness of the top layer may be at least 80, at least 84, at least 86, at least 88, or at least 90. The CIE L* lightness of the top layer may be up to 98, up to 96, up to 94, up to 92, or up to 90. The CIE L* lightness of the top layer may be in the range of 80-98, 84-94, 86-92, or 86-90. In one embodiment, the CIE L* lightness of the top layer is in the range of 84-94. The CIE L* lightness 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 L* lightness of the bottom layer. The CIE L* lightness 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 L* lightness of the bottom layer. The CIE L* lightness of the top layer may be greater 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 L* lightness of the top layer is greater than the CIE lightness of the bottom layer by a value in the range of 2.0 to 9.0.

[0092] 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 range from -3.5 to 7.5, from -2.2 to 6.6, from -1.8 to 5.6, or from -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.

[0093] In one embodiment, the representative test section has a CIE a* value that increases layer by layer from the top layer to the bottom layer when fully sintered by a rapid sintering process.

[0094] 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 up to 30, up to 26, up to 24, or up to 22. The CIE b* value of each layer may range from 1 to 30, 3 to 26, 4 to 24, or 11 to 22. In one embodiment, the CIE b* value of each layer may range from 3 to 26.

[0095] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1; and The representative test section, when fully sintered by the rapid sintering process, has a CIE L* lightness, and the CIE L* lightness of the layer meets one or more of the CIE L* lightness profiles A2.1 to J2.1 defined in Table B1 herein.

[0096] Such a set of CIE L* lightness profiles A2.1-J2.1 (or A2.2-J2.2), optionally in combination with other sets of profiles as described herein, is advantageous in that it provides for most patients a suitable selection of aesthetic appearances that match the appearance of natural teeth, e.g., in terms of lightness. A set of CIE L* lightness profiles C2.1-H2.1 (or C2.2-H2.2), e.g., F1.1 or G1.1 (or F1.2 or G1.2), is believed to be particularly advantageous in that it provides for a large subgroup of all patients a suitable selection of aesthetic appearances that match the appearance of natural teeth, e.g., in terms of lightness.

[0097] [Table 3]

[0098] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1; and The representative test section, when fully sintered by a rapid sintering process, has a CIE L* lightness, and the CIE L* lightness of the layer satisfies one or more CIE L* lightness profiles A2.2 to J2.2 defined in Table B2 herein.

[0099] [Table 4]

[0100] In one embodiment, the pre-sintered multi-layer dental mill blank is comprised of the following layers: a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1, wherein the CIE L* lightness of the layers meets one or more of the CIE L* lightness profiles A.2.1 to J2.1 defined in Table B1 herein or A2.2 to J2.2 defined in Table B2 herein. In one embodiment, the pre-sintered multi-layer dental mill blank is comprised of the following layers: a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1, wherein the CIE L* lightness of the layers meets one or more of the CIE L* lightness profiles C2.1 to H2.1 (e.g., profiles F2.1 or G2.1) defined in Table B1 herein or C2.2 to H2.2 (e.g., F2.2 or G2.2) defined in Table B2 herein.

[0101] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1; and The representative test section, when fully sintered by the rapid sintering process, has a CIE a* value, and the CIE a* value of the layer satisfies one or more of the CIE a* value profiles A3.1 to J3.1 defined in Table C1 herein.

[0102] [Table 5]

[0103] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1; and The representative test section, when fully sintered by the rapid sintering process, has a CIE a* value, and the CIE a* value of the layer satisfies one or more of the CIE a* value profiles A3.2 to J3.2 defined in Table C2 herein.

[0104] [Table 6]

[0105] In one embodiment, the pre-sintered multi-layer dental mill blank is composed of the following layers: top layer L4, middle layer L3, middle layer L2, bottom layer L1, and the CIE a* values ​​of the layers satisfy one or more of the CIE a* value profiles A3.1 to J3.1 defined in Table C1 herein or A3.2 to J3.2 defined in Table C2 herein.

[0106] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1; and The representative test section, when fully sintered by a rapid sintering process, has a CIE b* value, and the CIE b* value of the layer satisfies one or more of the CIE b* value profiles A4.1 to J4.1 defined in Table D1 herein.

[0107] [Table 7]

[0108] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1; and The representative test section, when fully sintered by a rapid sintering process, has a CIE b* value where the CIE b* value of the layer satisfies one or more of the CIE b* value profiles A4.2 to J4.2 of Table D2.

[0109] [Table 8]

[0110] In one embodiment, the pre-sintered multi-layer dental mill blank is comprised of the following layers: top layer L4, middle layer L3, middle layer L2, bottom layer L1, and the CIE b* values ​​of the layers satisfy one or more of the CIE b* value profiles A4.1 to J4.1 as defined in Table D1 herein or A4.2 to J4.2 as defined in Table D2 herein.

[0111] The CIE L*a*b* values ​​of the layers may satisfy a specific combination of the CIE L*a*b* value profile defined herein. The presintered multi-layer dental mill blank may comprise the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1; and The representative test section, when fully sintered by the rapid sintering process, has CIE L*a*b* values, and the CIE L*a*b* values ​​of the layer satisfy one or more of the optical property profiles a to j defined in Table E1 herein.

[0112] [Table 9]

[0113] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1; and The representative test section, when fully sintered by the rapid sintering process, has CIE L*a*b* values, and the CIE L*a*b* values ​​of the layer satisfy one or more of the optical property profiles aa to jj defined in Table E2 herein.

[0114] [Table 10] The CIE L* lightness profiles A2.2 to J2.2, the CIE a* value profiles A3.2 to J3.2, and the CIE b* value profiles A4.2 to J4.2 are as defined in Tables B2 to D2 herein.

[0115] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1; and The representative test section, when fully sintered by the rapid sintering process, has CIE L*a*b* values ​​and contrast ratios of the layer that satisfy one or more of the optical property profiles A-J in Table F1.

[0116] Such a set of optical property profiles A-J (or Aa-Jj) is advantageous in that it offers a suitable selection of aesthetic appearances that match the appearance of natural teeth, e.g., in terms of translucency and color, for most patients. A set of optical property profiles C-H (or Cc-Hh), e.g., F or G (or Ff or Gg), is considered to be particularly advantageous in that it offers a suitable selection of aesthetic appearances that match the appearance of natural teeth, e.g., in terms of translucency and color, for a large subgroup of all patients.

[0117] [Table 11] The contrast ratio profiles A1.1 to J1.1, the CIE L* lightness profiles A2.1 to J2.1, the CIE a* value profiles A3.1 to J3.1, and the CIE b* value profiles A4.1 to J4.1 are as defined in Tables A1 to D1 herein.

[0118] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1; and The representative test section, when fully sintered by the rapid sintering process, has CIE L*a*b* values ​​and contrast ratios of the layer that satisfy one or more of the optical property profiles Aa to Jj in Table F2.

[0119] [Table 12] The contrast ratio profiles A1.2 to J1.2, the CIE L* lightness profiles A2.2 to J2.2, the CIE a* value profiles A3.2 to J3.2, and the CIE b* value profiles A4.2 to J4.2 are as defined in Tables A2 to D2 herein.

[0120] In one embodiment, the pre-sintered multi-layer dental mill blank is comprised of the following layers: a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1, wherein the CIE L*a*b* values ​​and contrast ratios of the layers satisfy one or more of optical property profiles A-J defined in Table F1 herein or Aa-Jj defined in Table F2 herein. In one embodiment, the pre-sintered multi-layer dental mill blank is comprised of the following layers: a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1, wherein the CIE L*a*b* values ​​and contrast ratios of the layers satisfy one or more of optical property profiles C-H defined in Table F1 herein (e.g., F or G), or Cc-Hh defined in Table F2 herein (e.g., Ff or Gg).

[0121] In addition to or instead of the CIE L*a*b* values ​​described herein, the representative test sections, when fully sintered by a rapid sintering process, may have further properties, such as contrast ratio, number of pores per grain, or mechanical properties, as described herein.

[0122] 1.5 Number of pores per grain One embodiment of the present invention is a pre-sintered multi-layer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; each layer comprising zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; The presintered multi-layer dental mill blank is characterized by providing a representative test section in each layer, and a representative test section of the top layer and / or an intermediate layer adjacent to the top layer, when fully sintered by a rapid sintering process, has a number of pores per grain of less than 0.25.

[0123] The yttria content of the layers can increase from the bottom layer to the top layer, such that the bottom layer has a lower yttria content than at least one intermediate layer, which in turn has a lower yttria content than the top layer. In one embodiment, the pre-sintered multi-layer dental mill blank includes multiple intermediate layers, and the yttria content of each intermediate layer does not increase from layer to layer in the direction from bottom to top layer. However, the yttria content of each layer preferably increases from bottom to top layer.

[0124] One embodiment of the present invention is a pre-sintered multi-layer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; each layer comprising zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; The presintered multi-layer dental mill blank is characterized by providing a representative test section in each layer, and a representative test section of the top layer and / or an intermediate layer adjacent to the top layer, when fully sintered by a rapid sintering process, has a number of pores per grain of less than 0.25.

[0125] In one embodiment, a representative test section of the top layer, when fully sintered by a rapid sintering process, has less than 0.25 pores per grain. In one embodiment, a representative test section of the intermediate layer adjacent to the top layer, when fully sintered by a rapid sintering process, has less than 0.25 pores per grain. In one embodiment, a representative test section of the top layer and the intermediate layer adjacent to the top layer, when fully sintered by a rapid sintering process, has less than 0.25 pores per grain.

[0126] Representative test sections of the top layer and / or intermediate layer adjacent to the top layer are fully sintered by a rapid sintering process 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(s) having a number of pores per grain as defined herein.

[0127] 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 with desirable optical properties by a rapid sintering process. In particular, the mill blank may be suitable for preparing dental restorations with a more translucent incisal or occlusal zone (especially the portion of the incisal zone prepared from the top layer) by a rapid sintering process, which is highly desirable from an aesthetic point of view. While not wishing to be bound by theory, it is believed that residual pores in a fully sintered dental restoration (e.g., the pores seen in Figures 7-9) may diffract or scatter light in undesirable ways. Therefore, it is believed that the optical properties of a fully sintered dental restoration, such as its translucency, may be detrimental.

[0128] As used herein, the number of "pores" per crystal grain refers to the number of pores having a diameter in the range of 2 to 1000 nm. The pores may be intergranular or intragranular. An "intergranular pore" is a pore located between two or more different crystal grains, for example, a pore located at the boundary between two or more different crystal grains. An "intragranular pore" is a pore located within a crystal grain.

[0129] The number of pores per grain, or the number of intragranular pores per grain, is preferably determined by microstructural analysis of the surface (also referred to herein as a "region of interest (ROI)") of a fully sintered representative test section using a scanning electron microscope (SEM), as described in the "Measurement Methods" section below. The surface of a fully sintered representative test section preferably has a diameter of at least 50 μm. 2 , for example, 50 to 2000 μm 2の範囲 (e.g., 500 to 2000 μm 2 range), 50 to 1500 μm 2 range (e.g., 500 to 1500 μm 2 range), 50 to 1000 μm 2 Range: 50~500μm 2 range, or 50 to 300 μm 2The surface may be selected so that the surface grains 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 1.2-2.5 μm or 1.2-2.2 μm), or at least 1.4 μm (e.g., in the range of 1.4-2.5 μm or 1.4-2.2 μm). The number average grain size may be determined as described in the "Measurement Methods" section herein below. Yttria-stabilized zirconia grains having a relatively high yttria content (e.g., as in the range of 5Y-YSZ materials) are believed to grow faster during a rapid sintering process (e.g., the sintering process defined in Table 5 herein), resulting in larger grain sizes after sintering compared to yttria-stabilized zirconia grains with lower yttria contents. Additionally, multiple surfaces of a fully sintered representative test section (e.g., 50-300 μm) are measured. 2 It is also possible to select two, three, four or more surfaces (which may have surfaces in the range of 0.01, 0.1, 0.2, 0.3, 0.4 or 0.5) and determine the number of pores per grain (or the number of intragranular pores per grain) for one of each surface, and then calculate the number of pores per grain for the combined surfaces.

[0130] The number of pores per grain in the top layer may be less than 0.20, less than 0.15, less than 0.10, less than 0.05, or less than 0.02. Similarly, the number of pores per grain in an intermediate layer adjacent to the top layer may be 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 representative test sections in each layer, which, when fully sintered by a rapid sintering process, have a number of pores 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.

[0131] A representative test section of the top layer and / or intermediate layer adjacent to the top layer, when fully sintered by a rapid sintering process, may have less than 0.20, 0.15, 0.10, 0.05, or 0.02 intragranular pores per grain. In one embodiment, a representative test section of the top layer, when fully sintered by a rapid sintering process, may have less than 0.20, 0.15, 0.10, 0.05, or 0.02 intragranular pores per grain. In one embodiment, a representative test section of the intermediate layer adjacent to the top layer, when fully sintered by a rapid sintering process, has less than 0.20, 0.15, 0.10, 0.05, or 0.02 intragranular pores per grain. In one embodiment, representative test sections of the top layer and the intermediate layer adjacent to the top layer, when fully sintered by a rapid sintering process, have a number of intragranular pores per grain of less than 0.20, less than 0.15, less than 0.10, less than 0.05, or less than 0.02.

[0132] In addition to or instead of the number of pores per grain described herein, the representative test section, when fully sintered by a rapid sintering process, may have further properties, such as CIE L*a*b* values, contrast ratio, or mechanical properties, as described herein.

[0133] 1.6 Mechanical properties The representative test section may be characterized by specific mechanical properties such as flexural strength and / or fracture toughness when fully sintered by a rapid sintering process. Flexural strength and / or fracture toughness as defined herein for a layer refer to the flexural strength and fracture toughness of a representative test section where the layer has been fully sintered by a rapid sintering process, unless otherwise specified. Flexural strength may be determined in accordance with ISO 6872:2015. Fracture toughness (K Ic ) can be determined as described in the "Measuring Methods" section herein below.

[0134] A representative test section is designed to provide a specific bending strength and / or a specific fracture toughness (K) when fully sintered by a rapid sintering process. IC The 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 up to 1100 MPa, up to 1000 MPa, up to 800 MPa, or up to 750 MPa. The flexural strength of the top layer may be in the range of 500 to 1100 MPa, 550 to 1000 MPa, 575 to 800 MPa, or 600 to 750 MPa. The fracture toughness K of the top layer IC is at least 2.5MPa*m 1 / 2 , at least 2.7MPa*m 1 / 2 , or at least 2.8MPa*m 1 / 2 The fracture toughness of the top layer, K IC Maximum pressure is 3.5MPa*m 1 / 2 , maximum 3.3MPa*m 1 / 2 , or 3.2MPa*m 1 / 2 The fracture toughness of the top layer, K IC is 2.5~3.5MPa*m 1 / 2 , 2.7~3.3MPa*m 1 / 2 , or 2.8 to 3.2 MPa*m 1 / 2 Such strength and / or toughness may be desirable to provide sufficient strength and / or toughness to the incisal region of the dental restoration while preventing excessive wear on the occlusal surfaces of other teeth, such as opposing natural teeth.

[0135] The flexural strength of the bottom layer may be at least 900 MPa, at least 1000 MPa, or at least 1050 MPa. The flexural strength of the bottom layer may be up to 1500 MPa, up to 1300 MPa, or up to 1200 MPa. The flexural strength of the bottom layer may be in the range of 900 to 1500 MPa, 1000 to 1300 MPa, or 1050 to 1200 MPa. The fracture toughness K of the bottom layer IC is at least 3.6MPa*m 1 / 2 , at least 3.8MPa*m 1 / 2 , or at least 4.0 MPa*m 1 / 2The fracture toughness of the bottom layer K IC Maximum pressure is 5.5MPa*m 1 / 2 , maximum 4.8MPa*m 1 / 2 , maximum 4.6MPa*m 1 / 2 , or up to 4.4MPa*m 1 / 2 The fracture toughness of the bottom layer K IC is 3.6~5.5MPa*m 1 / 2 , 3.8~4.8MPa*m 1 / 2 , or 4.0~4.6MPa*m 1 / 2 , or 4.0 to 4.4 MPa*m 1 / 2 Such strength and / or toughness is highly desirable to provide sufficient mechanical stability in most dental restorative applications, including those requiring relatively small wall thicknesses, including but not limited to abutment-supported crowns or bridges, particularly those bridges where the connector dimensions between the different units of the bridge allow for the achievement of aesthetic clinical results.

[0136] In one embodiment, the fracture toughness K IC is at least 3.8MPa*m 1 / 2 , at least 4.0, or 3.8~4.8MPa*m 1 / 2 , or 4.0 to 4.4 MPa*m 1 / 2 and the bottom layer comprises yttria in an amount of at least 6.0 wt%, at least 6.4 wt%, or in the range of 6.0-7.5 wt%, or in the range of 6.4-7.2 wt%, based on the total weight of the bottom layer.

[0137] Fracture toughness K of at least one interlayer IC is at least 2.6MPa*m 1 / 2 , at least 2.8MPa*m 1 / 2 The fracture toughness K of at least one intermediate layer may be IC Maximum pressure is 4.4MPa*m 1 / 2 , maximum 4.2MPa*m 1 / 2 The fracture toughness K of at least one intermediate layer may be IC is 2.6~4.4MPa*m 1 / 2 , 2.8~4.2MPa*m1 / 2 The range may be:

[0138] Fracture toughness K of the intermediate layer adjacent to the top layer IC is at least 2.6MPa*m when measured with a 5kg load 1 / 2 , at least 2.8MPa*m 1 / 2、 or at least 2.9MPa*m 1 / 2 The fracture toughness K of the intermediate layer adjacent to the top layer can be IC is up to 3.6MPa*m when measured with a 5kg load 1 / 2 , maximum 3.4MPa*m 1 / 2、 or up to 3.3MPa*m 1 / 2 The fracture toughness K of the intermediate layer adjacent to the top layer can be IC is 2.6-3.6MPa*m when measured using a 5kg load 1 / 2 , 2.8~3.4MPa*m1 / 2、 or 2.9~3.3MPa*m1 / 2 The range may be:

[0139] Fracture toughness K of the intermediate layer adjacent to the bottom layer IC is at least 3.1MPa*m when measured with a 5kg load 1 / 2 , at least 3.3MPa*m 1 / 2、 or at least 3.4MPa*m 1 / 2 The fracture toughness of the intermediate layer adjacent to the bottom layer can be KIC is up to 4.2MPa*m when measured with a 5kg load 1 / 2 , maximum 4.0MPa*m 1 / 2、 or up to 3.8MPa*m 1 / 2 The fracture toughness K of the intermediate layer adjacent to the bottom layer can be IC is 3.1-4.2MPa*m when measured using a 5kg load 1 / 2 , 3.3~4.0MPa*m 1 / 2、 or 3.4~3.8MPa*m 1 / 2 The range may be:

[0140] The presintered multi-layer dental mill blank may include the following layers: top layer L4, middle layer L3, middle layer L2, bottom layer L1, where a representative test section of the layers, when fully sintered by a rapid sintering process, exhibits a fracture toughness K IC : The top layer L4 has a resistance of 2.5 to 3.5 MPa*m1 when measured using a 2.5 kg load. / 2. 2.7~3.3MPa*m1 / 2 , or 2.8 to 3.2 MPa*m 1 / 2 range, The middle layer L3 has a resistance of 2.6 to 3.6 MPa*m when measured using a load of 5 kg. 1 / 2 , 2.8~3.4MPa*m 1 / 2 , or 2.9 to 3.3 MPa*m 1 / 2 range, The intermediate layer L2 has a resistance of 3.1 to 4.2 MPa*m when measured using a 5 kg load. 1 / 2 , 3.3~4.0MPa*m 1 / 2 , or 3.4 to 3.8 MPa*m 1 / 2 range, The bottom layer L1 has a resistance of 3.6 to 4.8 MPa*m when measured using a load of 10 kg. 1 / 2 , 3.8~4.6MPa*m 1 / 2 , or 3.9 to 4.4 MPa*m 1 / 2 , and may have a range of

[0141] The representative test section, when fully sintered by a rapid sintering process, 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 the at least one middle layer, and the at least one middle layer has a higher flexural strength than the top layer. The representative test section, when fully sintered by a rapid sintering process, may have a flexural strength that decreases layer by layer from the bottom layer to the top layer.

[0142] A representative test section shows that when fully sintered by a rapid sintering process, the bottom layer has a higher fracture toughness (K) than at least one intermediate layer. ICand at least one intermediate layer has a higher fracture toughness K than the top layer. IC The fracture toughness K decreases from the bottom layer to the top layer, IC A representative test section shows that when fully sintered by a rapid sintering process, the fracture toughness K decreases layer by layer from the bottom layer to the top layer. IC may have:

[0143] In addition to, or instead of, the properties of the fully sintered representative test sections described herein, the presintered multilayer dental mill blank may be defined by its composition, as described herein, for example, in the following sections.

[0144] 2. Composition A presintered multi-layer dental mill blank according to the present invention may be defined by its components, the composition of its layers, and / or the composition of the dental mill blank as a whole, i.e., the combined composition of its layers.

[0145] 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 zirconia and yttria, with the yttria content of the layers increasing from the bottom layer to the top layer.

[0146] 2.1 Zirconia (ZrO2) and yttria (Y2O3) The pre-sintered multilayer dental mill blank may be a pre-sintered multilayer zirconia ceramic dental mill blank. Therefore, the pre-sintered multilayer dental mill blank may contain zirconia as a primary component. The pre-sintered multilayer dental mill blank may contain at least 80 wt%, at least 85 wt%, at least 89 wt%, up to 95 wt%, up to 93 wt%, or up to 91 wt%, or in a range of 80-95 wt%, 85-93 wt%, or 89-91 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0147] Each layer may comprise at least 80 wt%, at least 85 wt%, at least 87 wt%, or at least 88 wt% zirconia by weight, based on the total weight of the respective layer of the pre-sintered multilayer dental mill blank. Each layer may comprise up to 95 wt%, up to 94 wt%, up to 93 wt%, or up to 92 wt% zirconia by weight, based on the total weight of the respective layer of the pre-sintered multilayer dental mill blank. Each layer may comprise 80-95 wt%, 85-94 wt%, 87-93 wt%, or 88-92 wt% zirconia by weight, based on the total weight of the respective layer of the pre-sintered multilayer dental mill blank. For example, the top layer may comprise 80-92 wt% zirconia by weight, such as in the range of 85-91 wt%, e.g., 87-90 wt%. The bottom layer can include 85-94 wt% zirconia, such as in the range of 88-94 wt%, e.g., in the range of 90-92 wt%, based on the total weight of the bottom layer. Each of the at least one intermediate layer can include 82-94 wt% zirconia, such as in the range of 85-93 wt%, e.g., in the range of 87-92 wt%, based on the total weight of the respective layer of the at least one intermediate layer.

[0148] The zirconia is typically present in the form of yttria-stabilized zirconia. The pre-sintered multilayer dental mill blank may comprise at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 97 wt%, or in the range of 80-99.5 wt%, 90-99.5 wt%, 95-99.0 wt%, or 97-98.5 wt% yttria-stabilized zirconia by weight, based on the total weight of the pre-sintered multilayer dental mill blank. The pre-sintered multi-layer dental mill blank can include a combined weight 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 90-99.8 wt%, 95-99.5 wt%, or 98-99.2 wt% zirconia, yttria, and hafnium dioxide, based on the total weight of the pre-sintered multi-layer dental mill blank. Each layer can include a combined amount of at least 80 wt%, at least 90 wt%, at least 95 wt%, or at least 96 wt% zirconia and yttria, based on the total weight of the respective layer of the pre-sintered multi-layer dental mill blank. Each layer can include a combined amount of zirconia and yttria of up to 99.8 wt%, up to 99.5 wt%, up to 99.0 wt%, or up to 98.5 wt%, based on the total weight of the respective layer of the pre-sintered multi-layer dental mill blank. Each layer can include a combined amount of zirconia and yttria of 80-99.8 wt%, 90-99.5 wt%, 95-99.0 wt%, or 96-98.5 wt%, based on the total weight of the respective layer of the pre-sintered multi-layer dental mill blank.

[0149] Each layer of a pre-sintered multilayer dental mill blank typically contains zirconia and yttria. The yttria content of the layers may increase from the bottom layer to the top layer. The yttria content of the layers may increase from the bottom layer to the top layer, such that the bottom layer has a lower yttria content than at least one intermediate layer, and the at least one intermediate layer has a lower yttria content than the top layer. Accordingly, one embodiment of the present invention provides a pre-sintered multilayer dental mill blank including a top layer, a bottom layer, and at least one intermediate layer, each layer containing zirconia and yttria, and the yttria content of the layers increasing from the bottom layer to the 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. In one embodiment, the pre-sintered multilayer dental mill blank includes multiple intermediate layers, and the yttria content of each intermediate layer does not increase from the bottom layer to the top layer.

[0150] However, the yttria content of each layer preferably increases from the bottom layer to the top layer. The yttria content of the layers typically increases from the bottom layer to the top layer. Thus, yttria is typically present in different weight amounts in different layers of the presintered mill blank. Without wishing to be bound by theory, it is believed that the increasing yttria content from layer to layer contributes to a final dental restoration having a natural appearance with a gradual change in translucency from bottom to top.

[0151] The top layer may include at least 7.0 wt%, at least 8.0 wt%, at least 9.0 wt%, or at least 9.5 wt% yttria, based on the total weight of the top layer. The top layer may include up to 13.0 wt%, up to 12.0 wt%, up to 11.0 wt%, or up to 10.5 wt% yttria, based on the total weight of the top layer. The top layer may include a weight range of 7.0-13.0 wt%, 8.0-12.0 wt%, 9.0-11.0 wt%, or 9.5-10.5 wt% yttria, based on the total weight of the top layer.

[0152] The bottom layer may include at least 4.0 wt%, at least 5.0 wt%, at least 5.5 wt%, or at least 6.0 wt% yttria, based on the total weight of the bottom layer. The bottom layer may include up to 8.0 wt%, up to 7.5 wt%, up to 7.0 wt%, or up to 6.8 wt% yttria, based on the total weight of the bottom layer. The bottom layer may include 4.0-8.0 wt%, 5.0-7.5 wt%, 5.5-7.0 wt%, or 6.0-6.8 wt% yttria, based on the total weight of the bottom layer. In one embodiment, the top layer comprises yttria in a weight range of at least 9.0 wt%, e.g., at least 9.5 wt%, e.g., in the range of 9.5-10.5 wt%, based on the total weight of the top layer, and the bottom layer comprises yttria in a weight range of at most 7.0 wt%, e.g., in the range of 5.5-7.5 wt%, based on the total weight of the bottom layer. In one embodiment, the top layer comprises yttria in a weight range of 9.0-12.0 wt%, based on the total weight of the top layer, and the bottom layer comprises yttria in a weight range of 5.5-7.5 wt%, based on the total weight of the bottom layer.

[0153] Each of the at least one intermediate layer may include yttria 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 respective at least one intermediate layer. Each of the at least one intermediate layer may include yttria in an amount of up to 11.0 wt%, up to 10.5 wt%, up to 10.0 wt%, or 9.5 wt%, based on the total weight of the respective at least one intermediate layer. Each of the at least one intermediate layer may include yttria in an amount ranging from 5.0 to 11.0 wt%, 6.0 to 10.5 wt%, 6.5 to 10.0 wt%, or 7.0 to 9.5 wt%, based on the total weight of the respective at least one intermediate layer.

[0154] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1, which may comprise or consist of: the top layer L4 comprises yttria in an amount ranging from 7.0 to 13.0 wt%, 8.0 to 12.0 wt%, 9.0 to 11.0 wt%, or 9.5 to 10.5 wt%, based on the total weight of the top layer; the intermediate layer (L3) comprises yttria in a weight range of 6.0 to 11.0 wt%, 7.5 to 10.5 wt%, or 8.5 to 10.0 wt%, or 9.0 to 9.5 wt%, based on the total weight of the intermediate layer (L3); The intermediate layer (L2) comprises yttria in an amount ranging from 4.5 to 9.0 wt%, 5.5 to 8.0 wt%, 6.0 to 7.5 wt%, or 6.5 to 7.3 wt%, based on the total weight of the intermediate layer (L2); and The bottom layer L1 includes yttria by weight in the range of 4.0 to 9.0 wt%, 5.0 to 8.0 wt%, 5.5 to 7.5 wt%, or 6.0 to 6.8 wt%, based on the total weight of the bottom layer.

[0155] The yttria content of a layer can be defined by the difference in weight of the two layers, expressed as a percentage point(s). For example, the top layer can have an yttria content (in wt%), based on the total weight of the top layer, that is at least 1.0 percentage points, at least 2.0 percentage points, at least 2.5 percentage points, or at least 3.0 percentage points higher than the yttria content (in wt%) of the bottom layer, based on the total weight of the bottom layer. The top layer can have an yttria content (in wt%), based on the total weight of the top layer, that is up to 8.0 percentage points, up to 6.0 percentage points, up to 5.0 percentage points, or up to 4.0 percentage points higher than the yttria content (in wt%) of the bottom layer, based on the total weight of the bottom layer. The top layer can have an yttria content (in wt%), based on the total weight of the top layer, that is 1.0 to 8.0 percentage points, 2.0 to 6.0 percentage points, 2.5 to 5.0 percentage points, or 3.0 to 4.0 percentage points higher than the yttria content of the bottom layer, based on the total weight of the bottom layer.

[0156] Each layer can have a yttria content (wt%) that differs from the yttria content (wt%) 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 in the range of 0.3 to 3.0 percentage points, or 0.5 to 2.5 percentage points, where the yttria content of a layer is based on the total weight of that layer.

[0157] The yttria present in a layer of the pre-sintered multilayer dental mill blank, or throughout the pre-sintered multilayer dental mill blank, can be a composite yttria of type I and type II yttria. Similarly, the yttria content of a layer of the pre-sintered multilayer dental mill blank, or the yttria content of the pre-sintered multilayer dental mill blank as a whole, can be a composite yttria content of type I and type II yttria. In one embodiment, the top layer comprises yttria that is type I yttria, at least one middle layer comprises yttria that is a combination of type I and type II yttria, and the bottom layer comprises yttria that is a combination of type I and type II yttria.

[0158] Each layer of the pre-sintered multi-layer dental mill blank is preferably obtained from a yttria-stabilized zirconia powder or a mixture of different yttria-stabilized zirconia powders. Each layer of the pre-sintered multi-layer dental mill blank may be obtained 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% or more yttria-stabilized zirconia powder (5Y-YSZ). In one embodiment, each layer of the pre-sintered multi-layer dental mill blank can be made from a different yttria-stabilized zirconia powder or a different mixture selected from the group consisting of 3 mol% yttria-stabilized zirconia powder (3Y-YSZ), 4 mol% yttria-stabilized zirconia powder (4Y-YSZ), 5 mol% or greater yttria-stabilized zirconia powder (5Y-YSZ), and mixtures thereof. Such powders are commercially available, for example, from Daiichi Kigenso Kagaku Kogyo Co., Ltd. under the trade names HSY-3FSD-103, HSY-0250, and HSY-0451, respectively.

[0159] In one embodiment, the presintered multilayer dental mill blank comprises: a top layer L4 obtained from powder P3, an intermediate layer L3 obtained from a mixture of powders P2 and P3, an intermediate layer L2 obtained from a mixture of powders P1 and P2, a bottom layer L1 obtained from powder P1, and Powders P1 to P3 are three types of yttria-stabilized zirconia powders, with Powder P1 having an yttria content of 4.5 to 6.1 wt% (e.g., 4.9 to 6.0 wt%), Powder P2 having an yttria content of 6.2 to 7.9 wt% (e.g., 6.5 to 7.6 wt%), and Powder P3 having an yttria content of 8.0 to 11.0 wt% (e.g., 9.0 to 10.5 wt%).

[0160] Layers L4 to L1 may be obtainable 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, where each of powders P1 to P3 may optionally be treated with one or more additives (e.g., color additives, sintering accelerator precursors, and / or sintering inhibitor precursors).

[0161] In one embodiment, the presintered multilayer dental mill blank comprises: a top layer L4, which is a pre-sintered top powder layer of powder P3; an intermediate layer L3, which is a pre-sintered intermediate powder layer of a mixture of powders P2 / P3; an intermediate layer L2, which is a pre-sintered intermediate powder layer of the mixture of powders P1 / P2; a bottom layer L1, which is a pre-sintered bottom powder layer of powder P1; and Powders P1 to P3 are three types of yttria-stabilized zirconia powders, with Powder P1 having an yttria content in the range of 4.5 to 6.1 wt% (e.g., 4.9 to 6.0 wt%), Powder P2 having an yttria content in the range of 6.2 to 7.9 wt% (e.g., 6.5 to 7.6 wt%), and Powder P3 having an yttria content in the range of 8.0 to 11.0 wt% (e.g., 9.0 to 10.5 wt%).

[0162] The yttria contents (wt%) of Powders P1 and P2 and the yttria contents (wt%) of Powders P2 and P3 may 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, or at most 2.5 percentage points, for example, in the range of 0.7 to 3.0 percentage points, in the range of 1.0 to 2.8 percentage points, or in the range of 1.2 to 2.5 percentage points.

[0163] The mixture of powders P1 / P2 may contain powders P1 and P2 in a weight ratio of powder P1 to powder P2 ranging from 10:90 to 40:60, from 15:85 to 35:65, from 20:80 to 30:70, or from 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 ranging from 10:90 to 40:60, from 15:85 to 35:65, from 20:80 to 30:70, or from 22:78 to 28:72. In one embodiment, the powder P1 / P2 mixture contains powder P1 and powder P2 in a weight ratio of powder P1 to powder P2 ranging from 10:90 to 40:60, from 15:85 to 35:65, from 20:80 to 30:70, or from 22:78 to 28:72, and the powder P2 / P3 mixture contains powder P2 and powder P3 in a weight ratio of powder P2 to powder P3 ranging from 10:90 to 40:60, from 15:85 to 35:65, from 20:80 to 30:70, or from 22:78 to 28:72.

[0164] 2.2 Hafnium dioxide (HfO2) The pre-sintered multilayer dental mill blank can include hafnium dioxide. The hafnium dioxide can be part of or derived from a ceramic base 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 multilayer dental mill blank. For example, the hafnium dioxide can be part of the yttria-stabilized zirconia powder.

[0165] The pre-sintered multi-layer dental mill blank can contain hafnium dioxide in an amount of at least 0.5 wt%, at least 1.0 wt%, at least 1.2 wt%, up to 5.0 wt%, up to 3.0 wt%, or up to 2.0 wt%, or in a range of 0.5-5.0 wt%, 1.0-3.0 wt%, or 1.2-2.0 wt%, based on the total weight of the pre-sintered multi-layer dental mill blank.

[0166] Each layer of the pre-sintered multilayer dental mill blank can contain hafnium dioxide. The hafnium dioxide can be present in a specific weight ratio to zirconia. Each layer can contain hafnium dioxide to zirconia in a weight ratio ranging from 0:100 to 5:95, 1:99 to 4:96, 2:98 to 3:97, or 2:98, based on the total weight of the hafnium dioxide and zirconia in the respective layer of the pre-sintered multilayer 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%, up to 5.0 wt%, up to 3.0 wt%, or up to 2.0 wt%, for example, in the range of 0.1 to 5.0 wt%, for example, in the range of 0.5 to 3.0 wt%, for example, in the range of 1.5 to 2.0 wt%, based on the total weight of the respective layer.

[0167] Each layer may be defined by a combined amount of zirconia, yttria, and hafnium dioxide. Each layer may contain a combined amount of zirconia, yttria, 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 mill blank. Each layer may contain a combined amount of zirconia, yttria, and hafnium dioxide of up to 99.8 wt%, up to 99.6 wt%, up to 99.4 wt%, or up to 99.2 wt%, based on the total weight of the respective layer of the pre-sintered multilayer dental mill blank. Each layer may contain a combined amount of zirconia, yttria, and hafnium dioxide of 80-99.8 wt%, 90-99.6 wt%, 95-99.4 wt%, or 98-99.2 wt%, based on the total weight of the respective layer of the pre-sintered multilayer dental mill blank.

[0168] 2.3 Aluminum oxide (Al2O3) The pre-sintered multi-layer dental mill blank can include aluminum oxide, which may be part of or derived from the ceramic base 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.

[0169] The pre-sintered multilayer dental mill blank may contain at least 0.005 wt%, at least 0.02 wt%, or at least 0.05 wt%, up to 0.4 wt%, up to 0.2 wt%, or up to 0.1 wt%, or in the range of 0.005-0.4 wt% (e.g., 0.005-0.1 wt%), 0.02-0.2 wt%, or 0.05-0.1 wt%, aluminum oxide, based on the total weight of the pre-sintered multilayer dental mill blank.

[0170] The layers of the pre-sintered multilayer dental mill blank can have different aluminum oxide weight contents. The top layer can contain 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 contains a particularly low amount of aluminum oxide, the top layer or a portion thereof (e.g., a zone of a dental restoration at least partially obtained from the top layer) 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 reduced number of pores (i.e., intragranular and intergranular pores) present in the fully sintered top layer or a portion thereof. Pores are believed to diffract or scatter light in an undesirable manner in the fully sintered dental restoration and therefore may be detrimental to the optical properties of the fully sintered dental restoration, such as its translucency.

[0171] In one embodiment, the presintered multilayer dental mill blank comprises: The top layer and A bottom layer; at least one intermediate layer; Each layer comprises zirconia and yttria, the yttria content of the layers increasing 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.

[0172] The yttria content can increase from the bottom layer to the 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. Preferably, the yttria content of the layers increases from bottom to top.

[0173] In one embodiment, the presintered multilayer dental mill blank comprises: The top layer and A bottom layer; at least one intermediate layer; each layer comprises zirconia and yttria, the yttria content of the layers increasing 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.

[0174] The top layer may have a weight content of aluminum oxide that is less than the weight content of aluminum oxide of 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 to the bottom layer for at least two layers.

[0175] The bottom layer may have a weight content of aluminum oxide that is higher than the weight content of aluminum oxide of the top layer and the weight content of aluminum oxide of the intermediate layer adjacent to the top layer.

[0176] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1, which may comprise or consist of: Here, the aluminum oxide weight content in each of layers L1 and L2 is higher than the aluminum oxide weight content in layer L3, which is higher than the aluminum oxide weight content in layer L4.

[0177] The top layer may comprise aluminum oxide 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 aluminum oxide.

[0178] 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 up to 0.50 wt%, up to 0.40 wt%, up to 0.20 wt%, or up to 0.15 wt% aluminum oxide, based on the total weight of the bottom layer. The bottom layer may comprise 0.01-0.50 wt%, 0.02-0.40 wt%, 0.05-0.20 wt%, or 0.05-0.15 wt% aluminum oxide, based on the total weight of the bottom layer.

[0179] Each of the at least one intermediate layer may include 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 respective at least one intermediate layer. Each of the at least one intermediate layer may include up to 0.5 wt%, up to 0.20 wt%, or up to 0.15 wt% aluminum oxide based on the total weight of the respective at least one intermediate layer. Each of the at least one intermediate layer may include 0.01-0.5 wt%, 0.02-0.20 wt%, or 0.02-0.15 wt% aluminum oxide based on the total weight of the respective at least one intermediate layer.

[0180] The intermediate layer adjacent to 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 intermediate layer. The intermediate layer adjacent to the bottom layer may comprise up to 0.5 wt%, up to 0.20 wt%, or up to 0.15 wt% aluminum oxide, based on the total weight of the intermediate layer. The intermediate layer adjacent to the bottom layer may comprise 0.01-0.5 wt%, 0.02-0.20 wt%, or 0.05-0.15 wt% aluminum oxide, based on the total weight of the intermediate layer.

[0181] 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 up to 0.20 wt%, or up to 0.10 wt%, aluminum oxide, based on the total weight of the intermediate layer. The intermediate layer adjacent to the top layer may comprise 0.01-0.20 wt%, or 0.02-0.10 wt%, aluminum oxide, based on the total weight of the intermediate layer.

[0182] 2.4 Sintering accelerator The pre-sintered multilayer dental mill blank may contain a sintering accelerator. The sintering accelerator may be obtainable from a sintering accelerator precursor. The sintering accelerator may be obtained by converting the sintering accelerator precursor into a sintering accelerator during pre-sintering of the green body of the multilayer dental mill blank. The sintering accelerator precursor may be present in the powder layer of the green body. For example, the sintering accelerator precursor may be present on the surface of the powder particles in the powder layer. The sintering accelerator precursor may be added to the yttria-stabilized zirconia powder or a mixture of yttria-stabilized zirconia powders as a surface treatment agent (e.g., by treating the surfaces of the particles of the powder or powder mixture) prior to the pre-sintering step.

[0183] The pre-sintered multilayer dental mill blank can include 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% by weight of a sintering accelerator, or in the range of 0.02-0.8 wt%, 0.05-0.45 wt%, 0.10-0.30 wt%, or 0.15-0.25 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0184] The top layer of the pre-sintered multi-layer dental mill blank may include a sintering accelerator. In one embodiment, the pre-sintered multi-layer dental mill blank comprises: The top layer and A bottom layer; at least one intermediate layer; Each layer comprises zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; and The top layer includes a sintering aid.

[0185] The yttria content can increase from the bottom layer to the 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. Preferably, the yttria content of the layers increases from bottom to top.

[0186] In one embodiment, the presintered multilayer dental mill blank comprises: The top layer and A bottom layer; at least one intermediate layer; each layer comprises zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; and The top layer includes a sintering aid.

[0187] As the yttria content of the layers increases from bottom to top, the top layer has the highest yttria content of all layers. Generally, the time and / or temperature required to sinter a material containing zirconia and yttria to full density increases as the yttria content increases. Therefore, when a sintering promoter is included in the top layer, densification of the top layer or a prepared portion thereof (e.g., at least a portion of the incisal zone of a dental restoration precursor) can be achieved at a lower maximum sintering temperature and / or within a shorter sintering time. The sintering curve of the top layer or a prepared portion thereof can be shifted to a lower temperature. When a sintering promoter is present, the top layer of the prepared portion can be fully sintered in a shorter time while achieving very good optical properties.

[0188] Each layer of the pre-sintered multilayer dental mill blank can also contain a sintering accelerator. When a sintering accelerator is included in each layer, densification of each layer or its prepared portion (e.g., dental restoration precursor) can be achieved at a lower maximum sintering temperature and / or within a shorter sintering time. The sintering curve of each layer or its prepared portion can be shifted to a lower temperature. When a sintering accelerator is present in each layer, the layers of the prepared portion can be fully sintered in a short time while achieving very good optical properties.

[0189] Furthermore, it has been found that sintering accelerators (e.g., zinc oxide or gallium oxide) can be used in combination (e.g., in the bottom layer) with sintering inhibitors (e.g., type II yttria). This allows the sintering curve to be shifted to lower temperatures and still achieve good optical properties in the product despite the presence of the sintering inhibitor. While not wishing to be bound by theory, it is believed that sintering accelerators may be compatible with sintering inhibitors because sintering accelerators may have a more pronounced effect on the higher temperature range of the sintering curve (e.g., temperatures above 1100°C), while sintering inhibitors may have a more pronounced effect on the lower temperature range of the sintering curve (e.g., 900-1100°C).

[0190] The sintering aid is a metal oxide. The sintering aid may be zinc oxide (ZnO), gallium oxide (Ga2O3), or a combination thereof. It has been found that zinc oxide or gallium oxide, particularly zinc oxide, may be particularly useful as a sintering aid in the context of the present invention. In one embodiment, the sintering aid is zinc oxide, gallium oxide, or a combination thereof. In a preferred embodiment, the sintering aid is zinc oxide. In one embodiment, the top layer comprises a sintering aid that is zinc oxide, gallium oxide, or a combination thereof. In a preferred embodiment, the top layer comprises a sintering aid that is zinc oxide. In one embodiment, the top layer comprises a sintering aid that is not aluminum oxide.

[0191] Each of the layers of the presintered multi-layer dental mill blank can include a sintering aid (e.g., zinc oxide, gallium oxide, or a combination thereof). In one embodiment, each of the layers includes a sintering aid that is zinc oxide, gallium oxide, or a combination thereof (e.g., zinc oxide).

[0192] The top layer may contain a sintering promoter in a greater amount by weight than the bottom layer. For example, the weight [wt%] of the sintering promoter in the top layer and the weight [wt%] of the sintering promoter in the bottom layer may satisfy the following formula (A) or (B): w(SA-BL) / w(SA-TL) ≤ 0.85(A); w(SA-BL) / w(SA-TL) ≤ 0.80 (B); where w(SA-BL) is the weight of the sintering aid in the bottom layer based on the total weight of the bottom layer, and w(SA-TL) is the weight of the sintering aid in the top layer based on the total weight of the top layer.

[0193] In one embodiment, the weight of the sintering aid decreases from layer to layer from the top layer to the bottom layer.

[0194] The weight of the sintering accelerator in each layer can be adjusted so that at least a portion of the sintering curve, for example, the portion of the sintering curve associated with the maximum sintering rate, is aligned with one another. The maximum sintering rate can be calculated from the sintering curve of a rapid sintering process. The sintering curve can be obtained by plotting the relative compactness of the material as a function of sintering temperature. As used herein, the maximum sintering rate is the point on the sintering curve where the tangent to the curve has the greatest negative slope. The maximum sintering rate can be achieved at a temperature T of the rapid sintering process.

[0195] In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing a representative test section for each layer, and the weight of sintering accelerator 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 process, and the temperatures T of the representative test sections differ by no more than 40°C or no more than 25°C.

[0196] The layers of the presintered dental mill blank may contain a specific amount of sintering accelerator. The top layer may contain 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 may contain up to 0.8 wt%, up to 0.50 wt%, up to 0.30 wt%, or up to 0.20 wt%, based on the total weight of the top layer. The top layer may contain an amount of sintering accelerator ranging from 0.02 to 0.8 wt%, 0.05 to 0.50 wt%, 0.10 to 0.30 wt%, or 0.15 to 0.20 wt%, based on the total weight of the top layer.

[0197] The bottom layer may include the sintering accelerator 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 include the sintering accelerator in an amount of up to 0.80 wt%, up to 0.50 wt%, up to 0.30 wt%, or up to 0.17 wt%, based on the total weight of the bottom layer. The bottom layer may include the sintering accelerator in an amount ranging from 0.02-0.80 wt%, 0.02-0.50 wt%, 0.05-0.30 wt%, or 0.10-0.17 wt%, based on the total weight of the bottom layer.

[0198] Each layer may include the sintering accelerator 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 respective layer. Each layer may include the sintering accelerator in an amount of up to 0.8 wt%, up to 0.50 wt%, or up to 0.30 wt%, based on the total weight of the respective layer. Each layer may include the sintering accelerator in an amount ranging from 0.02-0.8 wt%, 0.05-0.50 wt%, or 0.10-0.30 wt%, based on the total weight of the respective layer.

[0199] The top layer may include a weight [wt%] of sintering accelerator, based on the total weight of the top layer, that is at least 0.010 percentage points, at least 0.020 percentage points, or at least 0.030 percentage points higher than the weight [wt%] of sintering accelerator present in the bottom layer, based on the total weight of the bottom layer. The top layer may include a weight [wt%] of sintering accelerator, based on the total weight of the top layer, that is up to 0.50 percentage points, up to 0.20 percentage points, or up to 0.10 percentage points higher than the weight [wt%] of sintering accelerator present in the bottom layer, based on the total weight of the bottom layer. The top layer may include a weight [wt%] of sintering accelerator, based on the total weight of the top layer, that is 0.010 to 0.5 percentage points, 0.020 to 0.20 percentage points, or 0.030 to 0.10 percentage points higher than the weight [wt%] of sintering accelerator present in the bottom layer, based on the total weight of the bottom layer.

[0200] It should be understood that when a pre-sintered multilayer dental mill blank according to an embodiment of the present invention, or any one of its layers, is described herein as including a particular type of sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof), this does not exclude that further, additional sintering promoters may be present (unless so expressly stated).

[0201] 2.5 Sintering inhibitors The pre-sintered multilayer dental mill blank may contain a sintering inhibitor. The sintering inhibitor may be derived from a sintering inhibitor precursor. The sintering inhibitor may be obtained by converting a sintering inhibitor precursor into a sintering inhibitor during pre-sintering of the green body of the multilayer 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 in the powder layer. The sintering inhibitor precursor may be added to the yttria-stabilized zirconia powder or a mixture of yttria-stabilized zirconia powders as a surface treatment agent (e.g., by treating the surfaces of the crystal grains of the powder or powder mixture) prior to the pre-sintering step.

[0202] The presintered multilayer dental mill blank can include 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 the range of 0.1-2.5 wt%, 0.2-2.0 wt%, 0.3-1.5 wt%, or 0.5-1.2 wt%, based on its total weight.

[0203] Sintering inhibitors may be present in one or more specific layers of a presintered dental mill blank. Sintering inhibitors may affect the sintering curve of a layer or prepared portion thereof primarily in the low temperature range (e.g., 900-1100°C), but also in the maximum shrinkage range. When a sintering inhibitor is present, the sintering curve of the ceramic material of a layer may be adjusted in the lower temperature range, thereby more closely matching the sintering curve of the ceramic material(s) of one or more other layers in that temperature range.

[0204] In one embodiment, the bottom layer includes a sintering inhibitor. In one embodiment, the bottom layer includes a sintering inhibitor, and each of the at least one intermediate layer includes a sintering inhibitor. It is also possible for each of the layers to include a sintering inhibitor. In one embodiment, the weight content of the sintering inhibitor decreases from the bottom layer to the top layer.

[0205] The bottom layer can include 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 an amount ranging from 0.4 to 2.5 wt%, 0.6 to 2.0 wt%, or 0.8 to 1.5 wt%, based on the total weight of the bottom layer.

[0206] Each of the at least one intermediate layer may include 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 an amount in the range of 0.02-2.0 wt%, 0.05-1.5 wt%, or 0.05-1.2 wt%, based on the total weight of the respective layer of the at least one intermediate layer.

[0207] The top layer can include a weight of sintering inhibitor in a range 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%, 0.01-1.0 wt%, 0.02-0.8 wt%, or 0.05-0.5 wt%, based on the total weight of the top layer.

[0208] The sintering inhibitor is a metal oxide. Examples of sintering inhibitors include La2O3, Yb2O3, Tm2O3, type II yttria, erbium oxide (Er2O 3)、 or any combination thereof. In one embodiment, the sintering inhibitor is La2O3, type II yttria, erbium oxide (Er2O3), or any combination thereof, and optionally the sintering inhibitor is type II yttria, erbium oxide, or a combination thereof. Preferably, the sintering inhibitor is type II yttria, optionally in combination with erbium oxide. In one preferred embodiment, the sintering inhibitor is a combination of type II yttria and erbium oxide.

[0209] Erbium oxide is also a coloring metal oxide. The weight of erbium oxide in the presintered multilayer dental mill blank or in any one of its layers may vary depending on the preshading of the dental mill blank. A layer of a dental mill blank that is more lightly preshaded may have a lower erbium oxide content than a layer of a dental mill blank that is more heavily preshaded. When the sintering inhibitor is a combination of type II yttria and erbium oxide, the weight of type II yttria in a layer (e.g., the bottom layer and / or each of at least one intermediate layer) can be adjusted to the weight of erbium oxide. This allows the sintering behavior of a layer, particularly the bottom layer, to be advantageously matched with the sintering behavior of one or more other layers of the mill blank.

[0210] In one embodiment, the bottom layer comprises a sintering inhibitor, which is a combination of type II yttria and erbium oxide, based on the total weight of the bottom layer, and the amount of type II yttria in the bottom layer is defined by the following formula: A II-Y-BL =A BL -(A E-BL -A E-TL ) In the formula, A II-Y-BLは、 is the molar amount of type II yttria in the bottom layer, and A BL is the molar amount of type II yttria in the bottom layer required to achieve the desired adjustment of the sintering curve in the absence of erbium oxide (i.e., in the case of a non-preshaded mill blank), and 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.

[0211] A BL A can be a molar amount equivalent to the weight of type II yttria in the range of 0.4 to 1.5 wt%, 0.6 to 1.2 wt%, or 0.8 to 1.1 wt%, based on the total weight of the bottom layer. E-BL and A E-TLmay be selected to match a dental shade, for example, a dental shade of the VITA classical A1-D4® shade guide using VITA Bleached Shades or a similar dental shade guide system manufactured by VITA Zahnfabrik. E-BL and A E-TL may be selected such that when fully sintered by a rapid sintering process, representative test sections of the bottom and top layers have CIE L*a*b* values ​​as described herein.

[0212] The bottom layer may include a sintering inhibitor that is type II yttria, optionally in combination with erbium oxide, and the bottom layer may include type II yttria 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 the ranges of 0.4-1.5 wt%, 0.6-1.2 wt%, or 0.8-1.1 wt%, based on the total weight of the bottom layer.

[0213] Each of the at least one intermediate layer may include a sintering inhibitor, type II yttria, optionally in combination with erbium oxide, and each of the at least one intermediate layer may include type II yttria in an amount of at least 0.02 wt%, at least 0.05 wt%, up to 1.0 wt%, up to 0.6 wt%, or 0.02-1.0 wt%, 0.05-1.0 wt%, or 0.05-0.6 wt%, based on the total weight of each of the at least one intermediate layer.

[0214] The top layer may include a sintering inhibitor that is type II yttria and / or erbium oxide, and the top layer may include type II yttria in a weight range of 0.00-0.03 wt%, 0.00-0.02 wt%, or 0.00-0.01 wt%, based on the total weight of the top layer. The top layer may be substantially free of type II yttria.

[0215] Pre-sintered multi-layer dental mill blanks consist of the following layers: Top tier L4, middle layer L3, A middle layer L2, a bottom layer L1, which may comprise or consist of: wherein each of layers L3-L1 comprises a sintering inhibitor that is type II yttria, optionally combined with erbium oxide; the intermediate layer (L3) comprises type II yttria in an amount ranging from 0.02 to 0.6 wt%, 0.05 to 0.4 wt%, or 0.06 to 0.2 wt%, based on the total weight of the intermediate layer (L3); the intermediate layer (L2) contains type II yttria in an amount ranging from 0.1 to 1.0 wt%, 0.2 to 0.8 wt%, or 0.4 to 0.6 wt%, based on the total weight of the intermediate layer (L2); the bottom layer L1 comprises type II yttria in an amount ranging from 0.4 to 1.5 wt%, 0.6 to 1.2 wt%, or 0.8 to 1.1 wt%, based on the total weight of the bottom layer; And optionally, the top layer L4 contains type II yttria in a weight range of 0.00 to 0.03 wt%, 0.00 to 0.02 wt%, or 0.00 to 0.01 wt%, based on the total weight of the top layer, or is substantially free of type II yttria.

[0216] Layers of presintered multilayer dental mill blanks containing specific amounts of type I yttria and type II yttria may be fully sintered, for example, by the rapid sintering process described herein, and the fracture toughness (e.g., fracture toughness K IC ) can be distinguished from comparable layers containing the same specific amount of yttria in the form of only type I yttria. For example, the bottom layer of a presintered multilayer dental mill blank may contain 5.6 wt% type I yttria and 0.9 wt% type II yttria. A representative test section of that bottom layer, when fully sintered by a rapid sintering process, exhibited a fracture toughness K ICA comparative bottom layer of a comparative presintered multilayer dental mill blank may contain 6.5 wt% type I yttria and no type II yttria. A representative test section of that comparative bottom layer, when fully sintered by the same rapid sintering process, may have a fracture toughness K IC The bottom layer may have a fracture toughness of -B. KIC -A is the fracture toughness KIC -B, it may be distinguishable from the bottom layer to which it is compared.

[0217] It should be understood that when a pre-sintered multilayer dental mill blank according to one embodiment of the present invention, or any one of its layers, is described herein as including a particular sintering inhibitor (e.g., type II yttria, erbium oxide, or a combination thereof), this does not exclude that further, additional sintering inhibitors may be present (unless so expressly stated).

[0218] 2.6 Colorants The pre-sintered multi-layer dental mill blank is typically pre-shaded. In one embodiment, the pre-sintered multi-layer dental mill blank is a pre-sintered, pre-shaded multi-layer dental mill blank. The dental mill blank, or a layer thereof, may be pre-shaded to match (or impart to at least a portion of) a tooth shade in a Vita Zahnfabrik VITA classical A1-D4® shade guide (and VITA Bleached Shades), or similar dental shade guide system. The dental 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 dental shade may also be a dental shade, such as a light dental shade, that is not part of a Vita Zahnfabrik VITA classical A1-D4® shade guide with VITA Bleached Shades, or similar dental shade guide system. The dental shade may be a laboratory light shade.

[0219] The pre-sintered multilayer dental mill blank can include a coloring metal oxide. Suitable coloring metal oxides 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 coloring metal oxide can be present 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 a range of 0.01-1.5 wt%, 0.02-1.0 wt%, or 0.05-0.8 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0220] The coloring metal oxide can include iron oxide. The pre-sintered multilayer dental mill blank can include 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 0.001-0.4 wt%, 0.005-0.2 wt%, or 0.02-0.1 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0221] The coloring metal oxide can include erbium oxide. The pre-sintered multilayer dental mill blank can include 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 0.01-1.2 wt%, 0.05-1.0 wt%, or 0.05-0.7 wt% erbium oxide by weight, based on the total weight of the pre-sintered multilayer dental mill blank.

[0222] Each layer of the presintered multilayer dental mill blank can include a coloring metal oxide, including erbium oxide and optionally iron oxide, 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 1.2 wt%, at most 1.0 wt%, or in a range of 0.01-1.5 wt%, 0.02-1.2 wt%, or 0.05-1.0 wt%, based on the total weight of the respective layer.

[0223] 2.7 Composition of combined layers As described herein, the presintered multilayer dental mill blank may include different components in different weight amounts. It is understood that the different components described herein are also disclosed herein in combination, including their weight amounts.

[0224] In one embodiment, the pre-sintered multi-layer dental mill blank comprises, based on a total weight of the pre-sintered multi-layer dental mill blank, 80-95 wt% zirconia, for example in the range of 85-93 wt%, e.g., in the range of 89-91 wt%, hafnium oxide, e.g., 5 wt% or less, e.g., 3 wt% or less, e.g., in the range 0.5-3.0 wt%, 5.0-10.0 wt% yttria, for example in the range of 6.0-9.0 wt%, for example in the range of 6.5-8.5 wt%; 0.4 wt% or less of aluminum oxide, for example in the range of 0.02-0.2 wt%, for example in the range of 0.05-0.1 wt%, 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.0 wt %, for example in the range of 0.05 to 0.8 wt %; 0.02-0.8 wt%, 0.05-0.45 wt%, 0.10-0.30 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof); wherein the weights of these components are optionally selected to total 100 wt %.

[0225] In one embodiment, the pre-sintered multi-layer dental mill blank comprises, based on a total weight of the pre-sintered multi-layer dental mill blank, 80-95 wt% zirconia, for example in the range of 85-93 wt%, e.g., in the range of 89-91 wt%, hafnium oxide, e.g., 5 wt% or less, e.g., 3 wt% or less, e.g., in the range 0.5-3.0 wt%, 5.0-10.0 wt% yttria, for example in the range of 6.0-9.0 wt%, for example in the range of 6.5-8.5 wt%; 0.4 wt% or less of aluminum oxide, for example in the range of 0.02-0.2 wt%, for example in the range of 0.05-0.1 wt%, 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.0 wt %, for example in the range of 0.05 to 0.8 wt %; 0.02-0.8 wt%, 0.05-0.45 wt%, 0.10-0.30 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof); 0.1-2.0 wt% sintering inhibitor, for example in the range of 0.2-1.5 wt%, for example in the range of 0.4-1.2 wt%, wherein the weights of these components are optionally selected to total 100 wt %.

[0226] In one embodiment, the pre-sintered multi-layer dental mill blank comprises, based on a total weight of the pre-sintered multi-layer dental mill blank, 80-95 wt% zirconia, for example in the range of 85-93 wt%, e.g., in the range of 89-91 wt%, hafnium oxide, e.g., 5 wt% or less, e.g., 3 wt% or less, e.g., in the range 0.5-3.0 wt%, 5.0-10.0 wt% yttria, for example in the range of 6.0-9.0 wt%, for example in the range of 6.5-8.5 wt%; 0.4 wt% or less of aluminum oxide, for example in the range of 0.02-0.2 wt%, for example in the range of 0.05-0.1 wt%, 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.0 wt %, for example in the range of 0.05 to 0.8 wt %; 0.02-0.8 wt%, 0.05-0.45 wt%, 0.10-0.30 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof); comprising (optionally consisting essentially of or consisting of) Here, yttria includes type II yttria, which is a sintering inhibitor; the pre-sintered multilayer dental mill blank comprises type II yttria in an amount ranging from 0.1 to 1.5 wt%, for example in the range of 0.2 to 1.2 wt%, for example in the range of 0.4 to 1.0 wt%, based on the total weight of the pre-sintered multilayer dental mill blank; The weights of these components are optionally selected to total 100 wt %.

[0227] In one embodiment, the pre-sintered multi-layer dental mill blank comprises, based on a total weight of the pre-sintered multi-layer dental mill blank, 80-94 wt% zirconia, for example in the range of 85-93 wt%, e.g., in the range of 89-91 wt%, hafnium oxide, e.g., 5 wt% or less, e.g., 3 wt% or less, e.g., in the range 0.5-3.0 wt%, 5.0-10.0 wt% yttria, for example in the range of 6.0-9.0 wt%, for example in the range of 6.5-8.5 wt%; 0.4 wt% or less of aluminum oxide, for example in the range of 0.02-0.2 wt%, for example in the range of 0.05-0.1 wt%, 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.0 wt %, for example in the range of 0.05 to 0.8 wt %; 0.02-0.8 wt%, 0.05-0.45 wt%, 0.10-0.30 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof); comprising (optionally consisting essentially of or consisting of) wherein the yttria comprises type II yttria as a sintering inhibitor, the coloring metal oxide comprises erbium oxide as a sintering inhibitor, and the pre-sintered multilayer dental mill blank comprises 0.1-2.0 wt% of a combination of type II yttria and erbium dioxide, for example in the range of 0.2-1.5 wt%, e.g., 0.4-1.2 wt%, based on the total weight of the pre-sintered multilayer dental mill blank; The weights of these components are optionally selected to total 100 wt %.

[0228] In one embodiment, the pre-sintered multi-layer dental mill blank comprises, based on a total weight of the pre-sintered multi-layer dental mill blank, 80-94 wt% zirconia, for example, in the range of 85-93 wt%, for example, in the range of 89-91 wt% zirconia; hafnium oxide, e.g., 5 wt% or less, e.g., 3 wt% or less, e.g., in the range 0.5-3.0 wt%, 5.0-10.0 wt% type I yttria, for example in the range of 5.5-8.5 wt%, e.g., in the range of 6.0-8.0 wt%; 0.4 wt% or less of aluminum oxide, for example in the range of 0.02-0.2 wt%, for example in the range of 0.05-0.1 wt%, 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.0 wt %, for example in the range of 0.05 to 0.8 wt %; 0.02-0.8 wt%, 0.05-0.45 wt%, 0.10-0.30 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof); 0.1-2.0 wt % of a sintering inhibitor (e.g., a combination of type II yttria and erbium oxide), for example in the range of 0.2-1.5 wt %, e.g., in the range of 0.4-1.2 wt %; comprising (optionally consisting essentially of or consisting of) The weights of these components are optionally selected to total 100 wt %.

[0229] 2.8 Layer-by-layer configuration As described herein, each of the layers may include different weights of different components. It is understood that the different components of each of the layers described herein, including their weights, are also disclosed herein in combination. It is further understood that the different layers as described herein are also disclosed herein in combination.

[0230] As noted above, sintering accelerators may be combined with sintering inhibitors in selected layers of the pre-sintered dental mill blank. By combining sintering accelerators and sintering inhibitors, the sintering curve of a ceramic material in one layer may be adjusted so that different portions of the sintering curve (associated with different temperature ranges of sintering) are more closely aligned with respective portions of the sintering curve of one or more ceramic materials in other layers.

[0231] In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing a representative test section for each layer, wherein the representative test section for the top layer and the representative test section for the bottom layer, when fully sintered by the rapid sintering process defined hereinabove, are each at a maximum sintering rate at a temperature T of the rapid sintering process and at a temperature T of the top layer (T TL ) and the temperature of the bottom layer (T BL ) differ by no more than 40° C. or no more than 25° C. In one embodiment, the pre-sintered multi-layer dental mill blank is characterized by providing a representative test section for each layer, each of the representative test sections, when fully sintered by a rapid sintering process as defined herein above, being at a maximum sintering rate at a temperature T of the rapid sintering process, the temperatures T for each of the layers differing by no more than 40° C. or no more than 25° C.

[0232] In one embodiment, the presintered multilayer dental mill blank comprises: The top layer and A bottom layer; at least one intermediate layer; each layer includes a sintering aid (e.g., zinc oxide, gallium oxide, or a combination thereof); and The bottom layer and, optionally, each of the at least one intermediate layer, includes a sintering inhibitor (eg, type II yttria).

[0233] In one embodiment, the presintered multilayer dental mill blank comprises: The top layer and A bottom layer; at least one intermediate layer; each layer comprising zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; each layer includes a sintering aid (e.g., zinc oxide, gallium oxide, or a combination thereof); Optionally, each layer comprises a colored metal oxide; and The bottom layer and, optionally, each of the at least one intermediate layer, includes a sintering inhibitor (eg, type II yttria).

[0234] The yttria content can increase from the bottom layer to the 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. Preferably, the yttria content of the layers increases from bottom to top.

[0235] In one embodiment, the presintered multilayer dental mill blank comprises: The top layer and A bottom layer; at least one intermediate layer; each layer comprising zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; each layer includes a sintering aid (e.g., zinc oxide, gallium oxide, or a combination thereof); Optionally, each layer comprises a colored metal oxide; and The bottom layer and, optionally, each of the at least one intermediate layer, includes a sintering inhibitor (eg, type II yttria).

[0236] In one embodiment, the top layer comprises, based on the total weight of the top layer: 80-92 wt% zirconia, for example in the range of 85-91 wt%, e.g., in the range of 87-90 wt%, hafnium dioxide, e.g., 3.0 wt% or less, e.g., in the range 0.5-3.0 wt%, but 5.0 wt% or less; 7.0-13.0 wt% yttria, for example in the range of 8.0-12.0 wt%, e.g., in the range of 9.0-11.0 wt%; less than 0.01 wt% aluminum oxide; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %; 0.02-0.80 wt % of a sintering promoter, for example, in the range of 0.02-0.50 wt %, e.g., in the range of 0.10-0.30 wt %, zinc oxide, gallium oxide, or a combination thereof; wherein the weight amounts of said components are optionally selected to total 100 wt %.

[0237] In one embodiment, the top layer comprises, based on the total weight of the top layer: 80-92 wt% zirconia, for example in the range of 85-91 wt%, e.g., in the range of 87-90 wt%, hafnium dioxide, e.g., 3.0 wt% or less, e.g., in the range 0.5-3.0 wt%, but 5.0 wt% or less; 7.0-13.0 wt% yttria, for example in the range of 8.0-12.0 wt%, e.g., in the range of 9.0-11.0 wt%; less than 0.01 wt% aluminum oxide; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %; 0.02-0.80 wt % of a sintering promoter, for example, in the range of 0.02-0.50 wt %, e.g., in the range of 0.10-0.30 wt %, zinc oxide, gallium oxide, or a combination thereof; wherein the weight amounts of said components are optionally selected to total 100 wt %.

[0238] In one embodiment, the bottom layer comprises, based on the total weight of the bottom layer: 85-94 wt% zirconia, for example in the range 88-94 wt%, e.g., in the range 90-92 wt%, hafnium dioxide, e.g., 3.0 wt% or less, e.g., in the range 0.5-3.0 wt%, but 5.0 wt% or less; 0.01-0.50 wt% aluminum oxide, for example in the range of 0.02-0.40 wt%, for example in the range of 0.05-0.20 wt%, 4.0-9.0 wt% yttria, for example in the range of 5.0-8.0 wt%, e.g., in the range of 5.5-7.5 wt%; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %; 0.02-0.80 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof), for example in the range of 0.02-0.50 wt%, e.g., in the range of 0.05-0.30 wt%, wherein the weight amounts of said components are optionally selected to total 100 wt %.

[0239] In one embodiment, the bottom layer comprises, based on the total weight of the bottom layer: 85-94 wt% zirconia, for example in the range 88-94 wt%, e.g., in the range 90-92 wt%, hafnium dioxide, e.g., 3.0 wt% or less, e.g., in the range 0.5-3.0 wt%, but 5.0 wt% or less; 0.01-0.50 wt% aluminum oxide, for example in the range of 0.02-0.40 wt%, for example in the range of 0.05-0.20 wt%, 4.0-9.0 wt% yttria, for example in the range of 5.0-8.0 wt%, e.g., in the range of 5.5-7.5 wt%; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %; 0.02-0.80 wt % of a sintering promoter, for example, in the range of 0.02-0.50 wt %, e.g., in the range of 0.05-0.30 wt %, zinc oxide, gallium oxide, or a combination thereof; wherein the weight amounts of said components are optionally selected to total 100 wt %.

[0240] The yttria in the bottom layer may include type II yttria, which is a sintering inhibitor, and the bottom layer may include type II yttria in an amount in the range of 0.4 to 1.5 wt%, for example, in the range of 0.6 to 1.2 wt%, for example, in the range of 0.8 to 1.1 wt%, based on the total weight of the bottom layer.

[0241] In one embodiment, each of the at least one intermediate layer comprises, based on the total layer weight of the respective layer of the at least one intermediate layer: 82-94 wt% zirconia, for example in the range of 85-93 wt%, e.g., in the range of 87-92 wt%, hafnium dioxide, e.g., 3.0 wt% or less, e.g., in the range 0.5-3.0 wt%, but 5.0 wt% or less; 0.01-0.50 wt% aluminum oxide, for example in the range of 0.02-0.20 wt%, for example in the range of 0.02-0.15 wt%, 5.0-11.0 wt% yttria, for example in the range of 6.0-10.5 wt%, e.g., in the range of 6.5-10.0 wt%; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %; 0.02-0.80 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof), for example in the range of 0.02-0.50 wt%, e.g., in the range of 0.05-0.30 wt%, wherein the weights of these components are optionally selected to total 100 wt %.

[0242] In one embodiment, each of the at least one intermediate layer comprises, based on the total layer weight of the respective layer of the at least one intermediate layer: 82-94 wt% zirconia, for example in the range of 85-93 wt%, e.g., in the range of 87-92 wt%, hafnium dioxide, e.g., 3.0 wt% or less, e.g., in the range 0.5-3.0 wt%, but 5.0 wt% or less; 0.01-0.50 wt% aluminum oxide, for example in the range of 0.02-0.20 wt%, for example in the range of 0.02-0.15 wt%, 5.0-11.0 wt% yttria, for example in the range of 6.0-10.5 wt%, e.g., in the range of 6.5-10.0 wt%; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %; 0.02-0.80 wt% zinc oxide, gallium oxide, or a combination thereof, for example in the range of 0.02-0.50 wt%, e.g., in the range of 0.05-0.30 wt%, wherein the weights of these components are optionally selected to total 100 wt %.

[0243] The yttria in each of the at least one intermediate layer may include type II yttria, which is a sintering inhibitor, and each of the at least one intermediate layer may include type II yttria in an amount in the range of 0.02 to 1.0 wt%, for example, in the range of 0.05 to 1.0 wt%, for example, in the range of 0.05 to 0.6 wt%, based on the total weight of the respective layer of the at least one intermediate layer.

[0244] In one embodiment, the presintered multi-layer dental mill blank comprises the following layers: The top layer L4, The middle layer L3, A middle layer L2, a bottom layer L1; Layers L4 through L1 comprise the ingredients defined in Table I herein below, the weights given being based on the total weight of the respective layer.

[0245] [Table 13]

[0246] In one embodiment, the presintered multi-layer dental mill blank comprises the following layers: The top layer L4, The middle layer L3, A middle layer L2, a bottom layer L1; Layers L4 through L1 comprise the ingredients defined in Table Ib herein below, the weights given being based on the total weight of the respective layer.

[0247] [Table 14]

[0248] In one embodiment, the presintered multi-layer dental mill blank comprises the following layers: The top layer L4, The middle layer L3, A middle layer L2, a bottom layer L1; Layers L4 through L1 comprise the ingredients defined in Table II herein below, the weights given being based on the total weight of the respective layer.

[0249] [Table 15]

[0250] In one embodiment, the presintered multi-layer dental mill blank comprises the following layers: The top layer L4, The middle layer L3, A middle layer L2, a bottom layer L1; Layers L4 through L1 comprise the ingredients defined in Table III herein below, the weights given being based on the total weight of the respective layer.

[0251] [Table 16]

[0252] In one embodiment, the presintered multi-layer dental mill blank comprises the following layers: The top layer L4, The middle layer L3, A middle layer L2, a bottom layer L1; Layers L4 through L1 comprise the ingredients defined in Table IV herein below, the weights given being based on the total weight of the respective layer.

[0253] [Table 17]

[0254] The weights of the components present in each of layers L1 through L4 defined in any one of Tables I, Ib, II, III and IV may be selected to total 100 wt %.

[0255] Layers L4 through L1 defined in any one of Tables I through IV may have an increasing yttria content from layer L1 to layer L4, such that layer L1 has a lower yttria content than layers L2 and L3, which in turn have a lower yttria content than layer L4. Layers L4 through L1 defined in any one of Tables I, Ib, II, III, and IV may have an increasing yttria content from layer L1 to layer L4.

[0256] Layers L4 through L1 defined in any one of Tables I, Ib, II, III and IV can consist essentially of or consist of the components defined in the respective table.

[0257] The coloring metal oxide present in each of layers L4 through L1 defined in any one of Tables I, Ib, II, III, and IV may include erbium oxide, which is a sintering inhibitor.

[0258] The yttria present in each of layers L3 through L1 as defined in any one of Tables I, Ib, II, III, and IV may include type II yttria, which is a sintering inhibitor, and optionally: the intermediate layer (L3) comprises type II yttria in an amount ranging from 0.02 to 0.6 wt%, 0.05 to 0.4 wt%, or 0.06 to 0.2 wt%, based on the total weight of the intermediate layer (L3); the intermediate layer (L2) contains type II yttria in an amount ranging from 0.1 to 1.0 wt%, 0.2 to 0.8 wt%, or 0.4 to 0.6 wt%, based on the total weight of the intermediate layer (L2); The bottom layer L1 includes type II yttria in an amount ranging from 0.4 to 1.5 wt%, 0.6 to 1.2 wt%, or 0.8 to 1.1 wt%, based on the total weight of the bottom layer L1; and The type II yttria content decreases from layer L3 to layer L1.

[0259] Any layer may contain unavoidable impurities (eg, SiO 2 , CaO, TiO 2 , or Na 2 O), for example, in a total amount of less than 0.1 wt %, based on the total weight of the respective layer.

[0260] 3. Morphology, Structure, and Lamination The presintered multi-layer dental mill blank according to the present invention comprises a top layer, a bottom layer and at least one intermediate layer.

[0261] The number of the at least one intermediate layer can range from 1 to 10 intermediate layers, such as from 1 to 5 intermediate layers. For example, the pre-sintered multi-layer dental mill blank can include 1, 2, or 3 intermediate layers. In one embodiment, the pre-sintered multi-layer dental mill blank includes 2 intermediate layers.

[0262] For example, a pre-sintered multilayer dental mill blank may include the following layers: a top layer L4, a middle layer L3, a middle layer L2, and a bottom layer L1. The numbering of layers L4 through L1 should be understood to define the stacking order of the layers in the pre-sintered multilayer dental mill blank (i.e., the order of layers L4 through L1 is L4, L3, L2, L1). The term "comprise" in this context should be understood to mean that the pre-sintered multilayer dental mill blank may include one or more additional middle layers, for example, located between layers L4 and L3, between layers L3 and L2, etc. The pre-sintered multilayer dental mill blank may be composed of the following layers: a top layer L4, a middle layer L3, a middle layer L2, and a bottom layer L1. The term "composed of" in this context should be understood to mean that the pre-sintered multilayer dental mill blank contains only the above-mentioned layers L4 through L1.

[0263] The layers of the presintered multilayer dental mill blank are not particularly limited in terms of their size and shape, so long as the dental mill blank is suitable for use in preparing a dental restoration precursor (e.g., using a CAD / CAM process). One or more of the layers may be non-planar. For example, one or more layers may have one or two surfaces (e.g., the interface between two layers or an outer surface, depending on the position of the layer within the mill blank) that are curved, e.g., have a positive or negative curvature (e.g., are convex or concave). It is also possible for one or more layers to have a height that increases uniformly or non-uniformly across at least a portion of the layer (e.g., conical).

[0264] One or more, and optionally all, of the layers can be substantially planar. In this context, "substantially planar" means that the layer is planar, subject to a 5% tolerance of the layer's average thickness. One or more, and optionally all, of the layers can be substantially planar over at least 70%, at least 80%, at least 90%, or at least 95% of the width and length of the layer (x and y directions). Due to unavoidable imperfect pressing of the green body, a layer that is substantially planar over a major portion of its width and length can exhibit curvature in the outer portion located at the surface of the dental mill blank. Such curvature can be seen in the comparative mill blank on the left side of Figure 2.

[0265] The layers of the presintered multi-layer dental mill blank may be arranged so that the boundaries of the layers are substantially parallel to one another.

[0266] Each layer of the presintered multilayer dental mill blank may have a specific height relative to the overall height of the dental mill blank. The overall height of the dental mill blank may be understood as the dimension of the dental mill blank in the layer stacking direction (z-direction). For example, in the case of a rectangular or disc-shaped dental mill blank, the overall height may be determined as the distance of a perpendicular line between the outer surface of the top layer and the opposing outer surface of the bottom layer, where the perpendicular line intersects all layers of the dental mill blank. The layer height may be understood as the maximum height of the layer in the layer stacking direction (z-direction). This is regardless of whether a relative height or an absolute height is defined herein. Therefore, the definition of layer height (e.g., relative height or absolute height) used herein does not necessarily imply that the layer height is constant, although this is possible.

[0267] Each of the layers may have a substantially constant height, where "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.

[0268] The bottom layer may have a height of at least 30%, at least 40%, at least 45%, at least 50%, or at least 52% of the total height of the pre-sintered multilayer dental mill blank. The bottom layer may have a height of up to 75%, up to 70%, up to 68%, or up to 66% of the total height of the pre-sintered multilayer dental mill blank. The bottom layer may have a height in the range of 30-75%, 40-75%, 45-70%, 50-68%, or 52-66% of the total height of the pre-sintered multilayer dental mill blank. In one embodiment, the bottom layer has a height of 52-66% of the total height of the pre-sintered multilayer dental mill blank.

[0269] The total height of the bottom layer and adjacent intermediate layer may be at least 55%, at least 60%, or at least 65% of the total height of the pre-sintered multilayer dental mill blank. The total height of the bottom layer and adjacent intermediate layer may be up to 85%, up to 80%, or up to 75% of the total height of the pre-sintered multilayer dental mill blank. The total height of the bottom layer and adjacent intermediate layer may be within a range of 55-85%, 60-80%, or 65-75% of the total height of the pre-sintered multilayer dental mill blank. In one embodiment, the total height of the bottom layer and adjacent intermediate layer may be within a range of 60-80% of the total height of the pre-sintered multilayer dental mill blank.

[0270] The top layer may have a height of at least 8%, at least 10%, at least 12%, at least 15%, or at least 17% of the total height of the pre-sintered multilayer dental mill blank. The top layer may have a height of up to 35%, up to 30%, up to 28%, up to 25%, or up to 23% of the total height of the pre-sintered multilayer dental mill blank. The top layer may have a height in the range of 8-35%, 10-30%, 12-28%, 15-25%, or 17-23% of the total height of the pre-sintered multilayer dental mill blank. In one embodiment, the top layer has a height in the range of 17-23% of the total height of the pre-sintered multilayer dental mill blank.

[0271] 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% of the total height of the pre-sintered multilayer dental mill blank. Each of the at least one intermediate layer may have a height of up to 25%, up to 20%, up to 15%, or up to 12% of the total height of the pre-sintered multilayer dental mill blank. Each of the at least one intermediate layer may have a height in the range of 2-25%, 4-20%, 6-15%, or 8-12% of the total height of the pre-sintered multilayer dental mill blank. In one embodiment, each of the at least one intermediate layer has a height in the range of 8-12% of the total height of the pre-sintered multilayer dental mill blank.

[0272] The combined intermediate layers may have a height of at least 5%, at least 10%, at least 14%, or at least 16% of the total height of the pre-sintered multilayer dental mill blank. The combined intermediate layers may have a height of up to 40%, up to 30%, up to 26%, or up to 25% of the total height of the pre-sintered multilayer dental mill blank. The combined intermediate layers may have a height in the range of 5-40%, 10-30%, 14-26%, or 16-25% of the total height of the pre-sintered multilayer dental mill blank. In one embodiment, the combined intermediate layers have a height in the range of 16-25% of the total height of the pre-sintered multilayer dental mill blank.

[0273] In one embodiment, the presintered multi-layer dental mill blank comprises the following layers: a top layer L4 having a height in the range of 12-28%, for example in the range of 15-25%, for example in the range of 17.5-23.5%; an intermediate layer L3 having a height in the range of 4 to 20%, for example in the range of 6 to 15%, for example in the range of 8.5 to 12%; an intermediate layer L2 having a height in the range of 4 to 20%, for example in the range of 6 to 15%, for example in the range of 8.5 to 12%; a bottom layer L1 having a height in the range of 45 to 70%, for example in the range of 50 to 68%, for example in the range of 52.5 to 65.5%, Here, all layer heights are relative to the total height of the pre-sintered multi-layer dental mill blank and are selected to add up to 100%.

[0274] 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.

[0275] The bottom layer may have a height of at least 1 mm, at least 5 mm, at least 7 mm, or at least 9 mm. The bottom layer may have a height of up to 20 mm, up to 15 mm, up to 12 mm, or up to 3 mm. The bottom layer may have a height in the range of 1-20 mm, 5-20 mm, 7-15 mm, or 9-12 mm. The top layer may have a height of at least 1 mm, at least 2 mm, or at least 3 mm. The top layer may have a height of up to 8 mm, up to 5 mm, or up to 4 mm. The top layer may have a height in the range of 1-8 mm, 2-5 mm, or 3-4 mm. Each of the at least one intermediate layer may have a height in the range of 1-3 mm, for example, in the range of 1.5-2.0 mm. The combined intermediate layers may have a height of at least 2 mm, at least 3 mm, up to 6 mm, or up to 4 mm, for example, in the range of 2-6 mm or 3-4 mm.

[0276] In one embodiment, the presintered multi-layer dental mill blank comprises the following layers: a top layer L4 having a height in the range of 2 to 5 mm (for example, 3 to 4 mm); an intermediate layer L3 having a height in the range of 1 to 3 mm (for example, about 1.5 mm or about 2 mm); an intermediate layer L2 having a height in the range of 1 to 3 mm (for example, about 1.5 mm or about 2 mm); It comprises or consists of a bottom layer L1 having a height in the range of 1 to 20 mm (for example, in the range of 1 to 3 mm or in the range of 7 to 15 mm).

[0277] In one embodiment, the presintered multi-layer dental mill blank comprises the following layers: a top layer L4 having a height in the range of 2 to 5 mm (for example, 3 to 4 mm); an intermediate layer L3 having a height in the range of 1 to 3 mm (for example, about 1.5 mm or about 2 mm); an intermediate layer L2 having a height in the range of 1 to 3 mm (for example, about 1.5 mm or about 2 mm); a bottom layer L1 having a height in the range of 5 to 20 mm (for example in the range of 7 to 15 mm).

[0278] The pre-sintered multilayer dental mill blank is not particularly limited in terms of its size and shape, so long as it is suitable for use in preparing a dental restoration precursor (e.g., using a CAD / CAM process). The pre-sintered multilayer dental mill blank can have the form of, but is not limited to, a rectangular block, a disk, a cylinder, a dental preform (e.g., an abutment preform or tooth sector), a cone, a cone segment, a pyramid, or a pyramid segment. In one embodiment, the pre-sintered multilayer dental mill blank has the shape of a disk, a cylinder, or a rectangular block. For example, the pre-sintered multilayer dental mill blank can be, but is not limited to, a disk having a height in the range of 8 to 30 mm (e.g., about 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, 25 mm), e.g., in the range of 14 to 22 mm, and a diameter in the range of 70 to 150 mm, e.g., in the range of 90 to 110 mm, e.g., 98 mm.

[0279] The pre-sintered multilayer dental mill blank may be porous or have a porous structure, particularly an open-porous structure. The density of the pre-sintered multilayer dental mill blank may be at least 45%, at least 50%, at least 52%, up to 70%, up to 60%, or up to 55% of its theoretical density, such as in the range of 45-70% (e.g., 45-55%), 50-60%, or 52-55% (e.g., about 52% or about 53%). In one embodiment, the density of the pre-sintered multilayer dental mill blank is in the range of 45-55% of its theoretical density. In one embodiment, the density of the pre-sintered multilayer dental mill blank is equal to or less than 53% of its theoretical density (e.g., 45-53% or 45-52%).

[0280] The pre-sintered multilayer dental mill blank can be obtained by pre-sintering a green body of a pre-sintered multilayer 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, up to 1100°C, up to 1000°C, up to 950°C, or up to 900°C, such as, for example, in the range of 700-1100°C, 750-1000°C, 800-950°C, or 825-900°C. In one embodiment, the pre-sintered multilayer dental mill blank can be obtained by pre-sintering a green body of a pre-sintered multilayer dental mill blank at a maximum pre-sintering temperature in the range of 800-950°C, such as, for example, in the range of 825-900°C. The maximum pre-sintering temperature can be achieved by heating the green body for, for example, 40-50 hours, at least 30 hours, or at least 40 hours. Thus, heating is typically carried out using a low heating rate, for example, in the range of 0.05-2 K / min, or in the range of 0.1-1.5 K / min. Heating may also be carried out stepwise using different heating steps with different heating rates in the range of 0.05-2 K / min, or in the range of 0.1-1.5 K / min. The maximum pre-sintering temperature may be held for a period in the range of 1 hour to 5 hours, for example, in the range of 2 hours to 3 hours.

[0281] The green body may be a shaped green body, such as a pressed green body (e.g., a uniaxially pressed green body), which may be obtained using a molding pressure in the range of 200 to 400 MPa, for example in the range of 250 to 350 MPa.

[0282] According to one embodiment of the present invention, there is provided a pre-sintered multi-layer dental mill blank obtainable by a process for preparing a pre-sintered multi-layer dental mill blank according to one embodiment of the present invention, which process is described in more detail in the following section.

[0283] II. Preparation process of pre-sintered multilayer dental mill blanks One aspect of the present invention provides a process for preparing a presintered multi-layer dental mill blank, the process comprising: a) providing three yttria-stabilized zirconia powders P1 to P3, where P1 has an yttria content in the range of 4.5 to 6.1 wt%, P2 has an yttria content in the range of 6.2 to 7.9 wt%, and P3 has an yttria content in the range of 8.0 to 11.0 wt%; b) preparing a green body, The top powder layer of powder P3, at least one intermediate powder layer of a powder mixture selected from the mixture of powders P2 / P3 and the mixture of powders P1 / P2, preparing a green body comprising 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.

[0284] It has been found that pre-sintered multilayer dental mill blanks based on the mixed pattern of Powders P1 to P3 of a process according to an embodiment of the present invention may be particularly suitable for preparing dental restorations having a desirable optical appearance and having a relatively large difference in one or more properties between the incisal or occlusal zone and the dentin zone of the dental restoration.

[0285] The expression "top powder layer of powder P3" should be understood to mean that the top powder layer does not contain an yttria-stabilized zirconia powder having a different yttria content than powder P3. This does not exclude that powder P3 can be a blend of different yttria-stabilized zirconia powders having an yttria content in the range of 8.0 to 11.0 wt%. Expressions such as "middle powder layer of a mixture of powders P2 / P3," "bottom powder layer of powder P1," etc., should be understood mutatis mutandis.

[0286] In one embodiment, the green body comprises: The top powder layer of powder P3, at least one intermediate powder layer of a powder mixture selected from the mixture of powders P2 / P3 and the mixture of powders P1 / P2, The bottom powder layer is made up of powder P1 or a mixture of powders P1 / P2.

[0287] In one embodiment, the green body comprises: 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; It comprises or consists of a bottom powder layer of powder P1.

[0288] Each of Powders P1 through P3 may have a combined amount of zirconia, yttria, and hafnium dioxide of at least 95 wt%, at least 98 wt%, at least 99 wt%, or in the range of 95-99.9 wt%, 98-99.9 wt%, or 99-99.8 wt%, based on the total weight of the respective powder. Powder P1 and / or Powder P2 may contain aluminum oxide in an amount of up to 0.40 wt%, up to 0.30 wt%, or up to 0.20 wt%, based on the total weight of the respective powder, or in the range of 0.01-0.40 wt%, 0.02-0.30 wt%, or 0.04-0.20 wt%, based on the total weight of the respective powder. Powder P3 may contain aluminum oxide in an amount of less than 0.05 wt%, e.g., less than 0.02 wt%, e.g., less than 0.01 wt%, based on the total weight of Powder P3.

[0289] The yttria content (wt%) of Powders P1 and P2 may differ from the yttria content (wt%) of Powders P2 and P3 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 0.7-3.0 percentage points, in the range of 1.0-2.8 percentage points, or in the range of 1.2-2.5 percentage points. Powder P1 may have an yttria content in the range of 4.9-6.0 wt%. Powder P2 may have an yttria content in the range of 6.5-7.6 wt%. Powder P3 may have an yttria content in the range of 9.0-10.5 wt%.

[0290] The mixture of powders P2 / P3 may contain powders P2 and P3 in a weight ratio of powder P2:powder P3 ranging from 10:90 to 40:60, from 15:85 to 35:65, or from 20:80 to 30:70. The mixture of powders P1 / P2 may contain powders P1 and P2 in a weight ratio of powder P1:powder P2 ranging from 10:90 to 40:60, from 15:85 to 35:65, or from 20:80 to 30:70. In one embodiment, the mixture of powders P2 / P3 may contain powders P2 and P3 in a weight ratio of powder P2:powder P3 ranging from 10:90 to 40:60, from 15:85 to 35:65, or from 20:80 to 30:70, and the mixture of powders P1 / P2 may contain powders P1 and P2 in a weight ratio of powder P1:powder P2 ranging from 10:90 to 40:60, from 15:85 to 35:65, or from 20:80 to 30:70.

[0291] The process may include adding one or more additives selected from the group consisting of sintering inhibitor precursors, sintering inhibitor precursors, and color additives to Powders P1 to P3 or mixtures thereof. Thus, Powders P1 to P3 or mixtures thereof present in different powder layers of the green body may be or have already been treated, for example by surface treatment, with one or more additives selected from the group consisting of sintering inhibitor precursors, sintering inhibitor precursors, and color additives. The one or more additives may be added in the form of an aqueous suspension, typically in the form of an aqueous solution.

[0292] The one or more additives may be added at different stages of the process. For example, one or more additives may be added to powders P1 through P3 before preparing a powder mixture of powders P1 / P2 and P2 / P3. However, it is also possible to first prepare a powder mixture of powders P1 / P2 and P2 / P3, and then add one or more additives to the powder mixture of powders P1 / P2 and P2 / P3, as well as to powder P1 and / or P3. In one embodiment, one or more additives are added to powders P1 through P3 before preparing a powder mixture of powders P1 / P2 and P2 / P3.

[0293] The process may include adding a sintering accelerator precursor to at least powder P3 or a mixture thereof. The process may typically include adding a sintering accelerator precursor to powders P1 to P3 or a mixture thereof before preparing the green body. Thus, powders P1 to P3, or a mixture thereof, present in different powder layers of the green body may already have been treated with a sintering accelerator precursor, for example by surface treatment. The sintering accelerator precursor may be added to the powder in the form of an aqueous suspension, typically an aqueous solution.

[0294] Thus, each of the powder layers of the green body may contain a sintering accelerator precursor. The sintering accelerator precursor may be added so that the powder layers have different weight contents of sintering accelerator precursor. For example, the top powder layer may have a higher weight content of sintering accelerator precursor than the bottom layer. The weight content of sintering accelerator precursor may increase from the bottom powder layer to the top powder layer. Thus, the weight of sintering accelerator precursor added to the powder may increase from P1 to P2 to P3.

[0295] Each powder layer of the green body can contain a sintering accelerator precursor. The sintering accelerator precursor is added in an appropriate amount by weight to each pre-sintered multilayer dental mill blank prepared by the process to provide a sintering accelerator content 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 a range of 0.02-0.8 wt%, 0.05-0.50 wt%, or 0.10-0.30 wt%, based on the total weight of each layer of the pre-sintered multilayer dental mill blank. Based on the target amount of sintering accelerator, one skilled in the art can calculate the amount of sintering accelerator precursor needed in a powder layer for a given sintering accelerator precursor and sintering accelerator combination (e.g., zinc nitrate as the sintering accelerator precursor and zinc oxide as the sintering accelerator) to achieve the desired sintering accelerator content.

[0296] The sintering promoter precursor can be a metal salt that can be converted to an oxide of the metal in the pre-sintering step of the process to provide the metal oxide that is the sintering promoter. 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 include, but are not limited to, metal phosphates, metal nitrates, metal sulfates, or metal halides.

[0297] In one embodiment, the sintering aid precursor is a zinc salt, a gallium salt, or a combination thereof. Thus, the sintering aid precursor may be a zinc salt, a gallium salt, or a combination thereof, which may be converted to a sintering aid that is zinc oxide, gallium oxide, or a combination thereof during the pre-sintering step of the process. In one embodiment, the process includes adding a sintering aid precursor to Powders P1 through P3 or a mixture thereof, wherein the sintering aid precursor is a zinc salt, a gallium salt, or a combination thereof.

[0298] In a preferred embodiment, the sintering accelerator precursor is a zinc salt. The zinc salt may be an inorganic zinc salt, such as zinc nitrate. The zinc salt may be water-soluble.

[0299] Each powder layer of the green body may contain a sintering promoter precursor, which may be a zinc salt, a gallium salt, or a combination thereof. The sintering promoter precursor may be present in each pre-sintered multilayer dental mill blank prepared by the process in an amount appropriate to provide 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 a range of 0.02-0.8 wt%, 0.05-0.50 wt%, or 0.10-0.30 wt%, based on the total weight of each layer of the pre-sintered multilayer dental mill blank.

[0300] The process may include adding a sintering inhibitor precursor to at least powder P1 or a mixture thereof. The process typically includes adding a sintering inhibitor precursor to powder P1 and powder P2, or a mixture thereof, before preparing the green body. Thus, powder P1 and powder P2, or a mixture thereof, present in different powder layers of the green body, may be or have already been treated with a sintering inhibitor precursor, for example, by surface treatment. The phrase "adding a sintering inhibitor precursor to powder P1 and powder P2, or a mixture thereof" should be understood broadly to encompass the option of adding one or more additives to powder P1 and powder P2 individually, or to any mixture containing either powder P1 or powder P2 (including a mixture of powder P2 / P3). The sintering inhibitor precursor may be added to the powder in the form of an aqueous suspension, typically an aqueous solution.

[0301] Thus, the bottom powder layer of the green body, and optionally the intermediate powder layer adjacent to the bottom layer, may contain a sintering inhibitor precursor. The sintering inhibitor precursor may be added so that the powder layers have different weight contents of sintering inhibitor precursor. For example, the bottom powder layer may have a higher weight content of sintering inhibitor precursor than the weight content of sintering inhibitor precursor in the top powder layer. The weight content of the sintering inhibitor precursor may decrease from the bottom powder layer to the top powder layer. Thus, the weight of sintering inhibitor precursor added to the powder may decrease from P1 to P2 to P3.

[0302] The bottom powder layer of green body powder P1 can contain a sintering inhibitor precursor in an amount appropriate to provide a sintering inhibitor in the bottom layer of the pre-sintered multi-layer dental mill blank prepared by the process, with a sintering inhibitor content 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 0.4-2.5 wt%, 0.6-2.0 wt%, or 0.8-1.5 wt%, based on the total weight of the bottom layer of the pre-sintered multi-layer dental mill blank.

[0303] The intermediate powder layer of the green body powder P1 / P2 mixture may contain a sintering inhibitor precursor in an amount appropriate to provide 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 the range of 0.02-2.0 wt%, 0.05-1.5 wt%, or 0.05-1.2 wt%, based on the total weight of each intermediate layer of the pre-sintered multilayer dental mill blank.

[0304] The intermediate powder layer of the green body powder P2 / P3 mixture may contain a sintering inhibitor precursor in an amount appropriate to provide 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 the range of 0.02-2.0 wt%, 0.05-1.5 wt%, or 0.05-1.2 wt%, based on the total weight of each intermediate layer of the pre-sintered multilayer dental mill blank.

[0305] The sintering inhibitor precursor can be a metal salt that can be converted to a metal oxide in the pre-sintering step of the process to provide the sintering inhibitor metal oxide. The metal salt can be a water-soluble metal salt. The metal salt can be an organic metal salt or an inorganic metal salt. Suitable inorganic metal salts include, but are not limited to, metal phosphates, metal nitrates, metal sulfates, or metal halides. The metal salt can be an yttrium salt, an erbium salt, a lanthanum salt, an ytterbium salt, a thulium salt, or any combination thereof. In one embodiment, the sintering inhibitor is an yttrium salt, an erbium salt, a lanthanum salt, or any combination thereof; optionally, the sintering inhibitor is an yttrium salt, an erbium salt, or a combination thereof.

[0306] In a preferred embodiment, the sintering inhibitor precursor is an yttrium salt, optionally in combination with an erbium salt. Thus, the sintering inhibitor precursor can be an yttrium salt that can be converted to the sintering inhibitor, type II yttria, during the pre-sintering step of the process. In one embodiment, the process includes adding a sintering inhibitor precursor to powder P1 and powder P2, or a mixture thereof, wherein the sintering inhibitor precursor is an yttrium salt. The yttrium salt can be an inorganic yttrium salt, such as yttrium nitrate. The yttrium salt can be water-soluble.

[0307] The bottom powder layer of green body powder P1 can contain a sintering inhibitor precursor, which is an yttrium salt, in an amount appropriate for providing a bottom layer of a pre-sintered multilayer dental mill blank prepared by the process with 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 0.4-1.5 wt %, 0.6-1.2 wt %, or 0.8-1.1 wt %, based on the total weight of the bottom layer of the pre-sintered multilayer dental mill blank.

[0308] The intermediate powder layer of the mixture of powders P1 / P2 of the green body can contain a sintering inhibitor precursor, which is an yttrium salt, in an amount appropriate for providing 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 0.1-1.2 wt %, 0.2-0.8 wt %, or 0.2-0.6 wt %, based on the total weight of each intermediate layer of the pre-sintered multilayer dental mill blank.

[0309] The intermediate powder layer of the green body powder P2 / P3 mixture may contain a sintering inhibitor precursor, which is an yttrium salt, in an amount appropriate for providing 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 0.02-0.5 wt %, or in the range of 0.05-0.2 wt %, based on the total weight of each intermediate layer of the pre-sintered multilayer dental mill blank.

[0310] The process may include not adding yttrium salt as a sintering inhibitor precursor to powder P3, and therefore the top powder layer may be substantially free of yttrium salt as a sintering inhibitor precursor.

[0311] The process may include adding a particular combination of a sintering accelerator precursor and a sintering inhibitor precursor to Powders P1 through P3 or a mixture thereof. In one embodiment, the process includes adding a sintering accelerator precursor (e.g., a zinc salt, a gallium salt, or a combination thereof) to Powders P1 through P3 or a mixture thereof, and adding a sintering inhibitor precursor (e.g., an yttrium salt) to Powder P1 or a mixture thereof. In one embodiment, the process includes adding a sintering accelerator precursor (e.g., a zinc salt, a gallium salt, or a combination thereof) to Powders P1 through P3 or a mixture thereof, and adding a sintering inhibitor precursor (e.g., an yttrium salt) to Powders P1 and P2 or a mixture thereof.

[0312] The process may include adding a color additive to powders P1 to P3 or a mixture thereof. The color additive may be added in the form of an aqueous solution. Suitable color additives include, for example, Fe 3+ , Mn 2+ , Pr 3+ , Tb 3+ , Cr 3+ and Er 3+The color additive may be a polyvalent ion of a 3d element and / or a 4f element in different valence states, such as, but not limited to, salts of these compounds, such as: In one embodiment, the color additive comprises an erbium compound and an iron compound.

[0313] 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 process may include debinding of the green body. Debinding may be performed separately from or in conjunction with pre-sintering, typically in conjunction with pre-sintering.

[0314] The preparation of the green body may include stacking powder layers in a mold. The preparation of the green body may include compressing the powder layers. Thus, the green body may be a compressed green body. Compression may be, but is not limited to, a uniaxial press. Compression may be performed at a pressure in the range of 200 to 400 MPa, for example, in the range of 250 to 350 MPa.

[0315] One or more, and optionally all, powder layers of the green body can be substantially planar. Each of the powder layers may 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 one another. In one embodiment, the powder layers are substantially planar and arranged so that the boundaries of the layers are substantially parallel to one another.

[0316] Presintering of the green body can be at least 700°C, at least 750°C, at least 800°C, at least 825°C, up to 1100°C, up to 1000°C, up to 950°C, up to 900°C, or a maximum temperature within the range of 700-1100°C, 750-1000°C, 800-950°C, or 825-900°C. The maximum temperature for presintering can be held for a period of time, such as from 1 hour to 5 hours, such as from 2 hours to 3 hours.

[0317] The pre-sintering process can be a pre-sintering process with a total sintering time in the range of 50 to 70 hours, such as in the range of 55 to 65 hours. The pre-sintering process can include one or more heating steps with a heating rate in the range of 0.05 to 2 K / min, or in the range of 0.1 to 1.5 K / min. The pre-sintering step typically includes one or more heating steps, e.g., three or more, or four or more heating steps, with different heating rates in the range of 0.05 to 2 K / min, or in the range of 0.1 to 1.5 K / min. The pre-sintering process can include heating steps with a heating rate in the range of 0.05 to 0.2 K / min, or in the range of 0.10 to 0.15 K / min, within the temperature range where debinding of the green body occurs. For example, suitable pre-sintering processes for pre-sintering the green body can be, but are not limited to, those described in Table V herein.

[0318] [Table 18]

[0319] The process may include one or more additional steps that are typical in the art, such as, but not limited to, mixing the powders in a mixing device, adjusting the particle size distribution of the powders (e.g., by sieving), and preparing the surface of the green body and / or presintered dental mill blank (e.g., by grinding or surface polishing).

[0320] The process may be a process for preparing a pre-sintered multilayer dental mill blank according to any one of the embodiments according to the present invention.

[0321] III. Dental restorations and processes for preparing dental restorations One aspect of the present invention provides a process for preparing a dental restoration, the process comprising the steps of: - machining the pre-sintered multilayer 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, - sintering the dental restoration precursor to provide a dental restoration.

[0322] Machining of the presintered multilayer dental mill blank can be performed by any conventional process for machining dental mill blanks, for example, by a CAD / CAM process. Machining can include, but is not limited to, cutting, drilling, and polishing the dental mill blank. The dental restoration precursor can be open-porous.

[0323] This sintering can be carried out by any sintering process known in the art for sintering dental restoration precursors, and particularly for sintering zirconia ceramic dental restoration precursors, without limitation. Typically, sintering is complete sintering to provide a fully sintered dental restoration. Sintering can be carried out at a maximum sintering temperature in the range of 1300°C to 1650°C, e.g., in the range of 1400°C to 1600°C. The maximum sintering temperature can be held for 2 minutes to 2 hours. The total sintering time can be less than 45 minutes, e.g., in the range of 10 to 45 minutes, or in the range of 10 to 30 minutes. Sintering can be a sintering process with a total sintering time of a rapid sintering process as defined herein. Typically, short sintering times are preferred to save time in preparing the dental restoration, but sintering can also be carried out for longer times, e.g., greater than 45 minutes, e.g., in the range of 1 to 10 hours or 2 to 8 hours.

[0324] In one embodiment, the sintering is a sintering process according to any one of the embodiments of the present invention, for example, as described in the following section.

[0325] The process may include further steps known in the art, such as, but not limited to, surface treating the dental restoration precursor (e.g., by surface polishing) or surface treating the dental restoration (e.g., staining, glazing, or veneering). In one embodiment, the process includes a step of surface treating the dental restoration precursor, such as manually surface treating the dental restoration precursor (e.g., manually surface polishing with a rotary dental surface polishing tool).

[0326] In one embodiment, the process comprises the following steps: - machining the pre-sintered multilayer dental mill blank according to any one of the embodiments of the present invention to provide a dental restoration precursor, - surface treating (e.g. manually surface treating) the dental restoration precursor, - sintering the surface treated dental restoration precursor to provide a dental restoration.

[0327] Another aspect of the present invention provides a dental restoration, which is obtainable by a process for preparing a dental restoration according to any one of the embodiments of the present invention.

[0328] A dental restoration may include multiple zones, such as two or more, or three or more different zones. A zone may have a different composition and / or one or more different properties (e.g., physical / mechanical properties, optical properties, or a combination thereof) from one or more of the other zones. The zones may correspond to one or more layers of a pre-sintered multi-layer dental mill blank from which the dental restoration is fabricated. The dental restoration may include an incisal zone, a transition zone, and a dentin zone. The transition zone may be located between the incisal zone and the dentin zone, and / or the incisal zone may be adjacent to the transition zone, which in turn may be adjacent to the dentin zone. The incisal zone may be made at least in part from the top layer of the pre-sintered multi-layer dental mill blank. The transition zone may be made at least in part from at least one middle layer of the pre-sintered multi-layer dental mill blank. The dentin zone may be made at least in part from the bottom layer of the pre-sintered multi-layer dental mill blank.

[0329] The dental restoration may have a desired color. At least a zone of the dental restoration or the dental restoration may have a color that matches a shade according to the VITA classical A1-D4® shade guide using VITA Bleached Shades 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 dental shade, such as a light dental shade, that is not part of the VITA classical A1-D4® shade guide using VITA Bleached Shades manufactured by Vita Zahnfabrik. The shade may be an experimental light shade.

[0330] The dental restoration may be, but is not limited to, a crown, partial crown, abutment, abutment crown, inlay, onlay, veneer, shell, or multi-unit framework, or bridge (e.g., two-unit bridge, three-unit bridge, or four-unit bridge), implant bridge, etc.

[0331] IV. Sintering Process Another aspect of the present invention provides a process for sintering a dental restoration precursor, the process having a total sintering time of less than 25 minutes and a maximum sintering temperature in the range of 1350°C to 1650°C; The process comprises: (i) heat treatment; (ii) a cooling treatment, The cooling treatment comprises a cooling step A, The cooling step A starts and ends within a temperature range between 1100° C. and the maximum sintering temperature and has a cooling rate A of at least 75 K / min.

[0332] It has been found that processes for sintering dental restoration precursors according to embodiments of the present invention (also referred to herein as "sintering processes") are suitable for preparing dental restorations having desirable properties, and in particular desirable optical properties (e.g., desirable translucency), in a short period of time.

[0333] The process may include subjecting the dental restoration precursor to a heating and cooling treatment.

[0334] The process may have a total sintering time of less than 20 minutes, less than 18 minutes, less than 16 minutes, or less than 15 minutes. The process may have a total sintering time of at least 5, 8, 10, or 12 minutes. The process may have a total sintering time ranging from 5 to less than 20 minutes, from 8 to less than 18 minutes, from 10 to less than 16 minutes, or from 12 to less than 15 minutes. "Total sintering time" is to be understood as defined in the "Definitions" section. The process may have a maximum sintering temperature in the range of 1400 to 1600°C, 1400 to 1560°C, 1400 to 1500°C, or 1425 to 1475°C. For example, the process may have a maximum sintering temperature of about 1450°C. It is believed that total sintering times as defined above allow for convenient preparation of dental restorations, and in particular, chairside preparation, allowing for the restoration to be provided to the patient in a single visit.

[0335] The sintering process includes a cooling process, which starts at a maximum sintering temperature and ends at a final temperature below the maximum sintering temperature. The cooling process includes one or more cooling steps, usually multiple cooling steps (e.g., two or three cooling steps). The cooling process may be followed by a cool-down, as defined herein. The cool-down is not part of the cooling or sintering process.

[0336] The cooling process includes a cooling step A. The cooling step A has a cooling rate A 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, up to 250 K / min, up to 200 K / min, up to 160 K / min, in the range of 100-250 K / min, in the range of 110-180 K / min, or in the range of 120-160 K / min (e.g., in the range of 125-140 K / min). For example, the cooling rate A can be about 130 K / min.

[0337] The cooling step A starts and ends within a temperature range between 1100°C and the maximum sintering temperature. This means that the cooling step A has a starting temperature and an ending temperature that fall within the temperature range between 1100°C and the maximum sintering temperature. The cooling step A may start and end in a temperature range between 1200°C and the maximum sintering temperature, or a temperature range between 1250°C and the maximum sintering temperature, or a temperature range between 1300°C and the maximum sintering temperature, or a temperature range between 1325°C and the maximum sintering temperature. In one embodiment, the cooling step A starts and ends within a temperature range between 1200°C and the maximum sintering temperature, and has a cooling rate A that is at least 100 K / min. The cooling step A may be carried out for a time period of at least 20 seconds, at least 30 seconds, at least 40 seconds, up to 3 minutes, up to 2 minutes, or up to 1 minute 30 seconds, such as in the range of 20 seconds to 3 minutes, 30 seconds to 2 minutes, or 40 seconds to 1 minute 30 seconds.

[0338] Cooling step A may be the first cooling step of the cooling process. Therefore, cooling step A may have a starting temperature that is the maximum sintering temperature. For example, cooling step A may have a starting temperature of 1450°C and an ending temperature of 1350°C.

[0339] The cooling treatment may include a cooling step B, which is carried out before or after, but usually after, cooling step A, and which has a cooling rate B that is lower than cooling rate A. It has been found that when the sintering process includes cooling step B as defined herein (optionally in addition to cooling step C as defined herein), dental restorations having advantageous optical properties are obtained. For example, cooling step B may be advantageous when sintering pre-shaded dental restoration precursors to achieve more preferred color properties, in particular when sintering pre-shaded dental restorations that contain iron oxide as the main component or one of the main components of the coloring oxide.

[0340] The cooling rate B can 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 the range of 30-110 K / min, in the range of 50-90 K / min, or in the range of 60-80 K / min.

[0341] Cooling step B can start and end in 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 end temperature that fall 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 a period of at least 45 seconds, at least 1 minute, at least 1 minute 30 seconds, up to 6 minutes, up to 4 minutes, or up to 3 minutes, such as in the range of 45 seconds to 6 minutes, 1 to 4 minutes, or 1 minute 30 seconds to 3 minutes.

[0342] Cooling step B may be performed immediately after cooling step A, i.e. the starting temperature of cooling step B may be the end temperature of cooling step A. However, it is also possible to have an intermediate cooling step between cooling steps A and B, although this is not limited to cooling step C as defined herein.

[0343] Thus, the cooling process may include a cooling step C. The cooling step C may be performed after the cooling step A and / or after the cooling step B. The cooling step C may start 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 the cooling step A (e.g., 1200°C, 1250°C, or 1300°C). The cooling step C may have a cooling rate C of up to 20 K / min, up to 10 K / min, up to 5 K / min, or about 0 K / min. Thus, the cooling step C may be a holding step (i.e., a step in which the temperature is kept substantially constant). The cooling step C may be performed for a period of at least 45 seconds, at least 1 minute, at least 1 minute 30 seconds, up to 5 minutes, up to 4 minutes, or up to 3 minutes, such as in the range of 45 seconds to 5 minutes, 1 minute to 4 minutes, or 1 minute 30 seconds to 3 minutes. It may be advantageous to perform a cooling step C when the dental restoration precursor is a pre-shaded dental restoration precursor, including, for example but not limited to, a bridge, including two or more such units.

[0344] The cooling process may include one or more additional cooling steps (including holding steps) performed before or after any one of the cooling steps A to C defined herein. In one embodiment, the cooling process includes cooling step A and cooling step B, optionally in combination with cooling step C.

[0345] The final temperature of the cooling treatment can be at least 1000°C, at least 1100°C, at least 1150°C, up to 1300°C, up to 1280°C, or up to 1250°C, such as in the range of 1000-1300°C, the range of 1100-1280°C, or the range of 1150-1250°C. For example, the final temperature of the cooling treatment can be 1200°C. The cooling treatment can be carried out for a period of at least 1 minute, at least 2 minutes, at least 2.5 minutes, up to 8 minutes, up to 6 minutes, or up to 4 minutes, such as in the range of 1 minute to 8 minutes, 2 minutes to 6 minutes, or 2.5 minutes to 4 minutes. The cooling procedure is typically followed by a cool-down, which can be carried out, at least partially, in an open sintering furnace. The cool-down can be considered complete at a temperature of about 400°C. The cool-down can be carried out in less than 10 minutes, such as less than 5 minutes, e.g., less than 3 minutes.

[0346] The sintering process involves a heat treatment, which begins at a starting temperature and ends at a maximum sintering temperature, and the starting temperature of the heat treatment can be in the range of 5°C to 30°C, for example 25°C.

[0347] The heat treatment includes one or more heating steps up to a maximum sintering temperature. The heat treatment typically includes a heating step A with a heating rate A of at least 150 K / min, at least 170 K / min, at least 190 K / min, up to 300 K / min, up to 250 K / min, or up to 220 K / min, such as in the range of 150-300 K / min, 170-250 K / min, or 190-220 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 within a temperature range between the start temperature of the heat treatment (e.g., 25°C) and the maximum sintering temperature. The heating step A can also start and end within a temperature range between the start temperature of the heat treatment and a temperature below 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 carried out for a period of at least 3 minutes, at least 4 minutes, up to 7 minutes, or up to 6 minutes, such as, for example, in the range of 3 to 7 minutes or 4 to 6 minutes.

[0348] The heat treatment may include two or more heating steps. The heat treatment may include a heating step A followed by a heating step B, where the heating step B has a heating rate B lower than the heating rate A. The heating rate B may be at least 50 K / min, at least 70 K / min, at least 90 K / min, up to 200 K / min, up to 150 K / min, up to 120 K / min, in the range of 50-200 K / min, in the range of 70-150 K / min, or in the range of 90-120 K / min. For example, the heating rate B may be 100 K / min. In one embodiment, the heat treatment includes a heating step A with a heating rate A of at least 170 K / min, followed by a heating step B, where the heating step B has a heating rate B of at least 70 K / min, lower than the heating rate A.

[0349] Heating step B may begin and end at a temperature range between the end temperature of heating step A and the maximum sintering temperature. Heating step B may begin immediately after heating step A, i.e., heating step B may have a starting temperature that is the end temperature of heating step A. Heating step B may end at the maximum sintering temperature. For example, heating step B may begin at a temperature of 1050°C and end at the maximum sintering temperature of 1450°C. Heating step B may be carried out for a period of at least 1 minute, at least 2 minutes, at least 3 minutes, up to 7 minutes, up to 6 minutes, or up to 5 minutes, such as in the range of 1 to 7 minutes, 2 to 6 minutes, or 3 to 5 minutes.

[0350] Furthermore, the heat treatment may include a heating step C after heating step B, where heating step C has a heating rate C lower than heating rate B. Heating step C may have a heating rate C of up to 40 K / min, up to 20 K / min, or up to 10 K / min. Heating step C may end at a maximum sintering temperature. Typically, heating step C is performed at the maximum sintering temperature with a heating rate C of approximately 0 K / min. Thus, heating step C is typically a holding step (i.e., a step in which the temperature is held substantially constant) at the maximum sintering temperature. The maximum sintering temperature may be held for at least 30 seconds, at least 1 minute, up to 5 minutes, up to 3 minutes, in the range of 30 seconds to 5 minutes, or in the range of 1 to 3 minutes. For example, the maximum sintering temperature may be held for approximately 2 minutes. At the end of the heat treatment, the dental restoration precursor is typically fully sintered.

[0351] The heat treatment may include one or more additional heating steps (including holding steps) performed before or after any one of heating steps A and B defined herein. The heat treatment may also include one or more additional controlled heating steps (including holding steps) performed before or after heating step C. If heating step C is a holding step at the maximum sintering temperature, there are no additional heating steps after heating step C. In one embodiment, the heat treatment consists of heating steps A through C. The heat treatment may be performed for a period of at least 5 minutes, at least 7 minutes, at least 8 minutes, up to 16 minutes, up to 14 minutes, or up to 12 minutes, such as in the ranges of 5 to 16 minutes, 7 to 14 minutes, or 8 to 12 minutes.

[0352] The heat treatment can be carried out at least in part at a pressure lower than that applied during other parts of the sintering process, such as during the cooling process. The lower pressure can be a pressure of 500 mbar or less, 200 mbar or less, 150 mbar or less, or 100 mbar or less, such as in the range of 0.1 to 500 mbar, 1 to 200 mbar, 10 to 150 mbar, or 50 to 100 mbar. The pressure can be adjusted by applying a vacuum. The vacuum can be applied before initiating the heat treatment or during the heat treatment, such as at a temperature range of 25 to 500°C or 25 to 100°C. When the heat treatment is carried out at least in part at a low pressure, as described herein, properties of the dental restoration, such as density or contrast ratio, can be further optimized.

[0353] The heat treatment may be partially carried out at a lower pressure. The low pressure may be applied in a temperature range between the starting temperature and a temperature lower than the maximum sintering temperature. The low 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 include heating step A and heating step B as defined herein, where heating step A is partially or completely, optionally completely, carried out at low pressure, and heating step B is partially carried out at low pressure. When part of the heat treatment is carried out at low pressure, the remaining part of the sintering process may be carried out at pressures above 900 mbar, as well as at ambient pressure. The heat treatment, and particularly the part(s) of the heat treatment not carried out at low pressure, may be carried out under a flow of gas such as air, oxygen-enriched air, or oxygen. The expected flow may have a flow rate in the range of 0.1 to 50 l / min, for example, in the range of 1 to 10 l / min, for example, in the range of 2 to 5 l / min.

[0354] 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%, up to 70%, up to 60%, or up to 55% of its theoretical density, such as in the range of 45-70% (e.g., 45-55%), 50-60%, or 52-55% (e.g., about 52% or about 53%). In one embodiment, the density of the pre-sintered multilayer dental mill blank is in the range of 45-55% of its theoretical density. The dental restoration precursor can be a pre-sintered ceramic material. Thus, the dental restoration precursor can be a pre-sintered ceramic material before being subjected to a sintering process. For example, the dental restoration precursor can be a ceramic material that has been pre-sintered at a maximum pre-sintering temperature of at least 700°C, at least 750°C, at least 800°C, at least 825°C, up to 1100°C, up to 1000°C, up to 950°C, up to 900°C, such as, for example, in the range of 700-1100°C, in the range of 750-1000°C, in the range of 800-950°C, or in the range of 825-900°C.

[0355] The dental restoration precursor may be, but is not limited to, a crown, partial crown, abutment, abutment crown, inlay, onlay, veneer, shell, or precursor to a multi-unit framework, or bridge (e.g., a two-unit bridge, a three-unit bridge, or a four-unit bridge), implant bridge, or the like.

[0356] The dental restoration precursor may be pre-shaded, 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 typically include iron oxide in combination with other colored metal oxides. It has been found that the sintering process according to embodiments of the present invention is particularly suitable for preparing dental restorations including colored metal oxides, particularly iron oxide, in a very short time.

[0357] The dental restoration precursor may be a zirconia dental restoration precursor, i.e., the dental restoration precursor may be zirconia-based. The dental restoration precursor may comprise zirconia and yttria. The dental restoration precursor may comprise zirconia and yttria and may include different sections, such as at least three sections, each section having a different yttria content. The different sections may be a top section (e.g., at least partially forming the incisal zone of the dental restoration), at least one middle section (e.g., at least partially forming the transition zone of the dental restoration), and a bottom section (e.g., at least partially forming the dentin zone of the dental restoration). The yttria content may increase from the bottom section to the middle section to the top section. The sintering process is suitable for sintering multi-section dental restoration precursors and / or dental restoration precursors obtained from a multi-layer dental mill blank, and therefore can provide dental restorations with a desirable optical appearance in a short period of time.

[0358] A dental restoration precursor may 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, may be pre-shaded. The multilayer dental mill blank, such as a pre-sintered multilayer dental mill blank, may include a top layer, a bottom layer, and at least one intermediate layer, each layer including zirconia and yttria, and the yttria content of the layers may increase from the bottom layer to the top layer.

[0359] The dental restoration precursor of the present invention can be prepared from a 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 a pre-sintered multi-layer dental mill blank according to one of the embodiments of the present invention, a natural and highly aesthetic dental restoration can be obtained in an extremely short time.

[0360] Another aspect of the present disclosure relates to a dental oven. The dental oven is configured to perform a process for sintering a dental restoration precursor according to any one of the embodiments described herein. The dental oven typically includes a sintering chamber, a heating device, and a control unit, and optionally includes a vacuum device or, optionally, is connected to a vacuum device. The dental oven is capable of sintering a dental restoration precursor according to the sintering process described herein. Specifically, the heating device may be capable of achieving a maximum sintering temperature of up to 1600°C, e.g., up to 1560°C. The heating device may be capable of achieving a heating rate of up to 300 K / min, e.g., up to 250 K / min. The dental oven may be configured to achieve a cooling rate of up to 180 K / min, e.g., up to 150 K / min. The vacuum device may be capable of achieving a vacuum of less than 500 mbar in the sintering chamber, e.g., less than 150 mbar, or in the range of 40-120 mbar. Such dental ovens (i.e., configurations not specifically configured to carry out the sintering process 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.

[0361] The control unit communicates with a dental oven device, such as the devices described herein. The control unit includes means adapted to cause the dental oven to perform a sintering process according to the embodiments described herein. Specifically, the control unit includes means adapted to cause the dental oven to perform a heating process, a cooling process, and optionally a pressure adjustment, as described herein. Thus, the control unit may include a data processing device (computer) configured to cause the dental oven to perform the sintering process. More specifically, the data processing device may have a memory unit and an arithmetic unit. The memory unit may include a computer-readable medium that stores a computer program. The computer program, and therefore the computer-readable medium, may include commands that, when the computer program is executed by the arithmetic unit, or more generally, by a computer, cause the arithmetic unit or computer to communicate with the dental oven device and perform the required process steps (e.g., heating process, cooling process, pressure adjustment, and opening and closing the chamber). In other words, a sequence of steps of a sintering process (e.g., the sequence of steps described in Table 5 herein) can be programmed on the data processing device (computer) of the dental oven. Thereby, the dental restoration precursor (placed in the sintering chamber) may be sintered using a sintering process according to the present disclosure.

[0362] Thus, another aspect of the present disclosure relates to a computer program comprising or storing commands that, when executed by a computer, cause the computer to perform a sintering process according to any one of the embodiments described herein. Yet another aspect of the present disclosure relates to a computer-readable medium storing or including commands that, when executed by a computer, cause the computer to perform a sintering process according to any one of the embodiments described herein. In particular, the computer is coupled to or in communication with a dental oven (such as the dental ovens described herein above) so that a dental restoration precursor can be sintered using the sintering process described herein. In another aspect of the present disclosure, a data processing device is provided that includes means for performing a sintering process according to any one of the embodiments described herein. In particular, the data processing device is coupled to or in communication with a dental oven (such as the dental ovens described herein above) so that a dental restoration precursor can be sintered using the sintering process described herein. The data processing device may be part of the control unit of the dental oven described herein above.

[0363] V. Non-Limiting Aspects and Embodiments of the Invention Further non-limiting embodiments of the present invention are defined in the following numbered items [1] to

[0174] and [1b] to [29b].

[0364] [1] A pre-sintered multilayer dental mill blank, The top layer and A bottom layer; at least one intermediate layer; characterizing the presintered multi-layer dental mill blank by providing a representative test section for each layer; The presintered multi-layer dental mill blank, wherein the representative test section has an increasing contrast ratio from the top layer to the bottom layer when fully sintered by a rapid sintering process.

[0365] [2] The pre-sintered multilayer dental mill blank according to item [1], wherein the contrast ratio increases from the top layer to the bottom layer such that the contrast ratio of the top layer is lower than the contrast ratio of the at least one intermediate layer, and the contrast ratio of the at least one intermediate layer is lower than the contrast ratio of the bottom layer.

[0366] [3] The pre-sintered multilayer dental mill blank according to item [1] or [2], wherein the contrast ratio increases from the top layer to the bottom layer.

[0367] [4] The pre-sintered multilayer dental mill blank according to any one of items [1] to [3], wherein the contrast ratio [%] of each layer is at least 56%, at least 61%, at least 62%, or at least 64%, and / or the contrast ratio [%] of each layer is at most 88%, at most 83%, at most 82%, or at most 79%.

[0368] [5] The pre-sintered multilayer dental mill blank according to any one of items [1] to [4], wherein the contrast ratio [%] of each layer is in the range of 56 to 88%, 61 to 83%, 62 to 82%, or 64 to 79%.

[0369] [6] The pre-sintered multilayer dental mill blank according to any one of items [1] to [5], wherein the contrast ratio [%] of the bottom layer differs 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, and / or the contrast ratio [%] of the bottom layer differs from the contrast ratio [%] 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.

[0370] [7] The pre-sintered multilayer dental mill blank according to any one of items [1] to [6], wherein the contrast ratio [%] of the bottom layer differs 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.

[0371] [8] The pre-sintered multilayer dental mill blank according to any one of items [1] to [7], wherein the contrast ratio of the bottom layer is at least 66%, at least 70%, at least 71%, or at least 74%, and / or the contrast ratio of the bottom layer is at most 88%, at most 83%, at most 81%, or at most 80%.

[0372] [9] The pre-sintered multilayer dental mill blank according to any one of items [1] to [8], wherein the contrast ratio of the bottom layer is in the range of 66% to 88%, 70 to 83%, 71 to 81%, or 74 to 80%.

[0373]

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

[0374]

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

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

[0375]

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

[11] , wherein the contrast ratio 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 ratio of the at least one intermediate layer is at most 83%, at most 79%, at most 78%, or at most 76%.

[0376]

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

[12] , wherein the contrast ratio 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%.

[0377]

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

[13] , wherein the contrast ratios [%] of each pair of adjacent layers differ 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.

[0378]

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

[14] , comprising at least two intermediate layers, wherein the contrast ratio [%] of one intermediate layer differs from the contrast ratio of another 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 by at most 12 percentage points, at most 10.0 percentage points, at most 9.0 percentage points, or at most 8.0 percentage points.

[0379]

[16] The following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1, and The pre-sintered multilayer dental mill blank according to any one of items [1] to

[15] , wherein the contrast ratios of the layers satisfy one or more of the contrast ratio profiles A1.1 to J1.1 (optionally one or more of the contrast ratio profiles C1.1 to H1.1) defined in Table A1 herein, or the contrast ratio profiles A1.2 to J1.2 (optionally one or more of the contrast ratio profiles C1.2 to H1.2) defined in Table A2 herein.

[0380]

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

[16] , wherein the representative test sections have a CIE L* lightness that increases layer by layer from the bottom layer to the top layer when fully sintered by a rapid sintering process.

[0381]

[18] A pre-sintered multilayer dental mill blank, The top layer and A bottom layer; at least one intermediate layer; characterizing the presintered multi-layer dental mill blank by providing a representative test section for each layer; The presintered multi-layer dental mill blank, wherein the representative test section has a CIE L* lightness that increases from the bottom layer to the top layer when fully sintered by a rapid sintering process.

[0382]

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

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

[0383]

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

[18] to

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

[0384]

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

[18] to

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

[0385]

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

[18] to

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

[0386]

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

[18] to

[22] , wherein the CIE L* lightness 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.

[0387]

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

[18] to

[23] , wherein the CIE L* color value 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 L* color value 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.

[0388]

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

[18] to

[26] , wherein the CIE L* color value 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.

[0389]

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

[18] to

[25] , wherein the CIE L* color value 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 L* color value of the top layer is at most 98, at most 96, at most 94, at most 92, or at most 90.

[0390]

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

[18] to

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

[0391]

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

[18] to

[27] , wherein the CIE L* color value 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 L* color value of the bottom layer, and / or the CIE L* color value 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 L* color value of the bottom layer.

[0392]

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

[18] to

[28] , wherein the CIE L* color value of the top layer is higher than the CIE L* color value 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.

[0393]

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

[29] , wherein the representative test section, when fully sintered by a rapid sintering process, 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.

[0394]

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

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

[0395]

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

[31] , wherein the representative test sections have CIE a* values ​​that increase layer by layer from the top layer to the bottom layer when fully sintered by a rapid sintering process.

[0396]

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

[32] , wherein the representative test section, when fully sintered by a rapid sintering process, has a CIE b* value, 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.

[0397]

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

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

[0398]

[35] The following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1, and The representative test section, when fully sintered by a rapid sintering process, has a CIE L* lightness, and the CIE L* of the layer satisfies one or more of the CIE lightness L* profiles A2.1 to J2.1 defined in Table B1 herein (optionally one or more of the CIE lightness L* profiles C2.1 to H2.1), or one or more of the CIE lightness L* profiles A2.2 to J2.2 defined in Table B2 herein (optionally one or more of the CIE lightness L* profiles C2.2 to H2.2).

[0399]

[36] The following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1, and The pre-sintered multilayer dental mill blank according to any one of items [1] to

[35] , wherein the representative test section, when fully sintered by a rapid sintering process, has a CIE a* value, and the CIE a* value of the layer satisfies one or more of the CIE a* value profiles A3.1 to J3.1 defined in Table C1 herein or one or more of the CIE a* value profiles A3.2 to J3.2 defined in Table C2 herein.

[0400]

[37] The following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1, and The pre-sintered multilayer dental mill blank according to any one of items [1] to

[36] , wherein the representative test section, when fully sintered by a rapid sintering process, has a CIE b* value, and the CIE b* value of the layer satisfies one or more of the CIE b* value profiles A4.1 to J4.1 defined in Table D1 herein or one or more of the CIE b* value profiles A4.2 to J4.2 defined in Table D2 herein.

[0401]

[38] The following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1, and The representative test section, when fully sintered by a rapid sintering process, has CIE L*a*b* values ​​and contrast ratios of the layers, the CIE L*a*b* values ​​and contrast ratios of the layers satisfying one or more of the optical property profiles A to J (optionally one or more of the optical property profiles C to H) defined in Table F1 herein, or one or more of the optical property profiles Aa to Jj (optionally one or more of the optical property profiles Cc to Hh) defined in Table F2 herein.

[0402]

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

[38] , wherein the pre-sintered multilayer dental mill blank is a pre-sintered multilayer zirconia ceramic dental mill blank.

[0403]

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

[39] , wherein each layer comprises zirconia and yttria, and the yttria content of the layers increases from the bottom layer to the top layer.

[0404]

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

[40] , wherein each layer comprises zirconia and yttria, and the yttria content of the layers increases from the bottom layer to the 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.

[0405]

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

[41] , wherein each layer comprises zirconia and yttria, and the yttria content of the layers increases from the bottom layer to the top layer.

[0406]

[43] A pre-sintered multilayer dental mill blank, The top layer and A bottom layer; at least one intermediate layer; each layer comprising zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; The presintered multi-layer dental mill blank is characterized by providing a representative test section for each layer; and The pre-sintered multilayer dental mill blank, wherein the representative test section of the top layer and / or an intermediate layer adjacent to the top layer, when fully sintered by a rapid sintering process, has a number of pores 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.

[0407]

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

[43] , wherein the yttria content of the layers increases from the bottom layer to the 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.

[0408]

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

[43] to

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

[0409]

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

[45] , wherein the representative test section layer of the top layer has a number of pores 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 process.

[0410]

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

[46] , wherein the representative test section of the intermediate layer adjacent to the top layer has a number of pores 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 process.

[0411]

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

[47] , wherein the representative test sections of the top layer and the intermediate layer adjacent to the top layer have a number of intragranular pores per grain 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 process.

[0412]

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

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

[0413]

[50] A pre-sintered multilayer dental mill blank, The top layer and A bottom layer; at least one intermediate layer; each layer comprises zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; and The presintered multi-layer dental mill blank, wherein the top layer comprises a sintering accelerator.

[0414]

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

[50] , wherein the yttria content of the layers increases from the bottom layer to the 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.

[0415]

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

[51] to

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

[0416]

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

[52] , wherein the top layer contains 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.

[0417]

[54] A pre-sintered multilayer dental mill blank, The top layer and A bottom layer; at least one intermediate layer; each layer comprising zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; The pre-sintered multi-layer dental mill blank, wherein the top layer comprises aluminum oxide in an amount of less than 0.01 wt %, based on the total weight of the top layer.

[0418]

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

[54] , wherein the yttria content of the layers increases from the bottom layer to the 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.

[0419]

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

[55] to

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

[0420]

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

[56] , wherein each layer contains a sintering accelerator.

[0421]

[58] the top layer contains a greater amount of the sintering accelerator than the bottom layer; and Optionally, the content of the sintering accelerator decreases from layer to layer from the top layer to the bottom layer.

[0422]

[59] characterizing the presintered multi-layer dental mill blank by providing a representative test section for each layer; Item

[57] or

[58] , wherein the weight of the sintering accelerator 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 a temperature T when fully sintered by a rapid sintering process, and the temperatures T of the representative test sections differ by no more than 40°C or no more than 25°C.

[0423]

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

[49] to

[59] , wherein the top layer comprises the sintering accelerator 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 accelerator 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.

[0424]

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

[49] to

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

[0425]

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

[57] to

[61] , wherein each layer contains the sintering accelerator 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 respective layer, and / or each layer contains the sintering accelerator 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 respective layer.

[0426]

[63] The pre-sintered multilayer dental mill blank according to any one of Items

[57] to

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

[0427]

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

[49] to

[63] , wherein the sintering accelerator can be obtained by converting a sintering accelerator precursor into the sintering accelerator when pre-sintering the green body of the multilayer dental mill blank.

[0428]

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

[49] to

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

[0429]

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

[49] to

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

[0430]

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

[66] , wherein each layer comprises a combined amount of zirconia, yttria, 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 mill blank, and / or each layer comprises a combined amount of zirconia, yttria, and hafnium 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 mill blank.

[0431]

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

[67] , wherein each layer contains a combined amount of zirconia, yttria, and hafnium dioxide of 80 to 99.8 wt%, 90 to 99.6 wt%, 95 to 99.4 wt%, or 98 to 99.2 wt%, based on the total weight of the respective layer of the pre-sintered multilayer dental mill blank.

[0432]

[69] each layer comprises at least 80 wt%, at least 85 wt%, at least 87 wt%, or at least 88 wt% zirconia by weight based on the total weight of the respective layer of the pre-sintered multi-layer dental mill blank; and / or each layer comprises up to 95 wt%, up to 94 wt%, up to 93 wt%, or up to 92 wt% zirconia by weight based on the total weight of the respective layer of the pre-sintered multi-layer dental mill blank; Alternatively, each layer contains zirconia in an amount ranging from 80 to 95 wt%, 85 to 94 wt%, 87 to 93 wt%, or 88 to 92 wt%, based on the total weight of the respective layer of the pre-sintered multilayer dental mill blank.

[0433]

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

[69] , wherein each layer contains hafnium dioxide to zirconia in a weight ratio ranging from 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 zirconia in the respective layer of the pre-sintered multilayer dental mill blank.

[0434]

[71] 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% yttria, based on the total weight of the top layer; and / or the top layer comprises, based on the total weight of the top layer, at most 13.0 wt%, at most 12.0 wt%, at most 11.0 wt%, or at most 10.5 wt% yttria. The pre-sintered multilayer dental mill blank according to any one of items [1] to

[70] .

[0435]

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

[71] , wherein the top layer contains yttria in an amount ranging from 7.0 to 13.0 wt%, 8.0 to 12.0 wt% (for example, within a range of 9.0 to 12.0 wt%), 9.0 to 11.0 wt%, or 9.5 to 10.5 wt%, based on the total weight of the top layer.

[0436]

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

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

[0437]

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

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

[0438]

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

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

[0439]

[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 contains 5.0 to 11.0 wt%, 6.0 to 10.5 wt%, 6.5 to 10.0 wt%, or 7.0 to 9.5 wt% yttria, based on the total weight of the respective layer of the at least one intermediate layer.

[0440]

[77] The pre-sintered multilayer 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 respective 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 respective layer of the at least one intermediate layer.

[0441]

[78] The following layers: The top layer L4, The middle layer L3, A middle layer L2, a bottom layer L1, and The top layer (L4) contains yttria in a range of 7.0 to 13.0 wt%, 8.0 to 12.0 wt%, 9.0 to 11.0 wt%, or 9.5 to 10.5 wt%, based on the total weight of the top layer; the intermediate layer (L3) contains yttria in a range of 6.0 to 11.0 wt%, 7.5 to 10.5 wt%, 8.5 to 10.0 wt%, or 9.0 to 9.5 wt%, based on the total weight of the intermediate layer (L3); and the intermediate layer (L2) contains yttria in a range of 6.0 to 11.0 wt%, 7.5 to 10.5 wt%, 8.5 to 10.0 wt%, or 9.0 to 9.5 wt%, based on the total weight of the intermediate layer (L2). The pre-sintered multilayer dental mill blank according to any one of items [1] to

[77] , wherein the bottom layer (L1) contains yttria in a range of 4.5 to 9.0 wt%, 5.5 to 8.0 wt%, 6.0 to 7.5 wt%, or 6.5 to 7.3 wt%, based on the total weight of the bottom layer (L1), and the bottom layer (L1) contains yttria in a range of 4.0 to 9.0 wt%, 5.0 to 8.0 wt%, 5.5 to 7.5 wt%, or 6.0 to 6.8 wt%, based on the total weight of the bottom layer (L1).

[0442]

[79] the top layer has an yttria content, based on the total weight of the top layer, that is at least 1.0 percentage points, at least 2.0 percentage points, at least 2.5 percentage points, or at least 3.0 percentage points higher than the yttria content of the bottom layer, based on the total weight of the bottom layer; and / or

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

[78] , wherein the top layer has an yttria 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 yttria content of the bottom layer, based on the total weight of the bottom layer.

[0443]

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

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

[0444]

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

[80] , wherein each layer has an yttria content that differs from the yttria 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 in the range of 0.3 to 3.0 percentage points, or 0.5 to 2.5 percentage points, wherein the yttria content of a layer is based on the total weight of the layer.

[0445]

[82] The following layers: a top layer L4 obtained from yttria-stabilized zirconia powder P3; an intermediate layer L3 obtained from a mixture of yttria-stabilized zirconia powder P2 and powder P3; an intermediate layer L2 obtained from a mixture of yttria-stabilized zirconia powder P1 and powder P2; a bottom layer L1 obtained from an yttria-stabilized zirconia powder P1, and The pre-sintered multilayer dental mill blank according to any one of items [1] to

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

[0446]

[83] The following layers: a top layer L4, which is a pre-sintered top powder layer of powder P3; an intermediate layer L3, which is a pre-sintered intermediate powder layer of a mixture of powders P2 / P3; an intermediate layer L2, which is a pre-sintered intermediate powder layer of the mixture of powders P1 / P2; a bottom layer L1, which is a pre-sintered bottom powder layer of powder P1; and The pre-sintered multilayer dental mill blank according to any one of items [1] to

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

[0447]

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

[82] and

[83] , wherein the yttria contents of Powders P1 and P2 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, in a range of 0.7 to 3.0 percentage points, in a range of 1.0 to 2.8 percentage points, or in a range of 1.2 to 2.5 percentage points, and the yttria contents of Powders P2 and P3 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, in a range of 0.7 to 3.0 percentage points, in a range of 1.0 to 2.8 percentage points, or in a range of 1.2 to 2.5 percentage points.

[0448]

[85] The pre-sintered multilayer dental mill blank according to any one of Items

[82] to

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

[0449]

[86] The pre-sintered multilayer 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.

[0450]

[87] The pre-sintered multilayer dental mill blank of item

[86] , wherein the bottom layer comprises a greater amount of the sintering inhibitor than the amount of the sintering inhibitor in the top layer, and optionally the amount of the sintering inhibitor decreases from the bottom layer to the top layer.

[0451]

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

[86] and

[75] , wherein the bottom layer comprises a 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 the range of 0.4-2.5 wt%, 0.6-2.0 wt%, or 0.8-1.5 wt%, based on the total weight of the bottom layer.

[0452]

[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 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 wt%, or in a range of 0.02 to 2.0 wt%, 0.05 to 1.5 wt%, or 0.05 to 1.2 wt%, based on the total weight of the respective layer of the at least one intermediate layer.

[0453]

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

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

[0454]

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

[86] to

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

[0455]

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

[91] , wherein each layer comprises a sintering promoter (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 yttria).

[0456]

[93] The 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 yttria, erbium oxide, or any combination thereof, optionally wherein the sintering inhibitor is La2O3, type II yttria, erbium oxide, or any combination thereof, optionally wherein the sintering inhibitor is type II yttria, erbium oxide, or a combination thereof.

[0457]

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

[86] to

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

[0458]

[95] The aluminum content of the top layer is the lowest among all layers; Optionally, the aluminum content of the layers increases layer by layer in at least two layers in a direction from the top layer to the bottom layer.

[0459]

[96] The following layers: Top tier L4, middle layer L3, middle layer L2, a bottom layer L1, comprising or consisting of: wherein the weight content of aluminum oxide in each of the layers L1 and L2 is higher than the weight content of aluminum oxide in the layer L3, and the weight content of aluminum oxide in the layer L3 is higher than the weight content of aluminum oxide in the layer L4;

[0023] The pre-sintered multilayer dental mill blank according to any one of items [1] to

[95] , wherein the weight content of aluminum oxide in each layer is determined based on the total weight of each layer.

[0460]

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

[96] , wherein the bottom layer contains 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, and / or 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.

[0461]

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

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

[0462]

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

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

[0463]

[0100] A pre-sintered multilayer dental mill blank as described in item

[99] , wherein each layer contains the coloring metal oxide 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 1.2 wt%, at most 1.0 wt%, or in the range of 0.01 to 1.5 wt%, in the range of 0.02 to 1.2 wt%, or in the range of 0.05 to 1.0 wt%, based on the total weight of the respective layer.

[0464]

[0101] A pre-sintered multilayer dental mill blank described in item

[99] or

[0100] , wherein the coloring metal oxide comprises iron oxide, manganese oxide, praseodymium oxide, chromium oxide, erbium oxide, terbium oxide, or a mixture thereof.

[0465]

[0102] The bottom layer comprises, based on the total weight of the bottom layer: 85-94 wt% zirconia, for example in the range 88-94 wt%, e.g., in the range 90-92 wt%, hafnium dioxide, e.g., 3.0 wt% or less, e.g., in the range 0.5-3.0 wt%, but 5.0 wt% or less; 0.01-0.50 wt% aluminum oxide, for example in the range of 0.02-0.40 wt%, for example in the range of 0.05-0.20 wt%, 4.0-9.0 wt% yttria, for example in the range of 5.0-8.0 wt%, e.g., in the range of 5.5-7.5 wt%; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %; 0.02-0.80 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof), for example in the range of 0.02-0.50 wt%, e.g., in the range of 0.05-0.30 wt%,

[0101] The pre-sintered multilayer dental mill blank according to any one of items [1] to

[0101] , wherein the weights of the components are optionally selected to total 100 wt%.

[0466]

[0103] The top layer comprises, based on the total weight of the top layer: 80-92 wt% zirconia, for example in the range of 85-91 wt%, e.g., in the range of 87-90 wt%, hafnium dioxide, e.g., 3.0 wt% or less, e.g., in the range 0.5-3.0 wt%, but 5.0 wt% or less; 7.0-13.0 wt% yttria, for example in the range of 8.0-12.0 wt%, e.g., in the range of 9.0-11.0 wt%; less than 0.01 wt% aluminum oxide; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %; 0.02-0.80 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof), for example in the range of 0.02-0.50 wt%, e.g., in the range of 0.10-0.30 wt%,

[0102] The pre-sintered multilayer dental mill blank according to any one of items [1] to

[0102] , wherein the weights of the components are optionally selected to total 100 wt%.

[0467]

[0104] each of the at least one intermediate layer, based on the total weight of the respective layer of the at least one intermediate layer: 82-94 wt% zirconia, for example in the range of 85-93 wt%, e.g., in the range of 87-92 wt%, hafnium dioxide, e.g., 3.0 wt% or less, e.g., in the range 0.5-3.0 wt%, but 5.0 wt% or less; 0.01-0.50 wt% aluminum oxide, for example in the range of 0.02-0.20 wt%, for example in the range of 0.02-0.15 wt%, 5.0-11.0 wt% yttria, for example in the range of 6.0-10.5 wt%, e.g., in the range of 6.5-10.0 wt%; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %; 0.02-0.80 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof), for example in the range of 0.02-0.50 wt%, e.g., in the range of 0.05-0.30 wt%,

[0103] The pre-sintered multilayer dental mill blank according to any one of items [1] to

[0103] , wherein the weights of the components are optionally selected to total 100 wt%.

[0468]

[0105] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0104] , comprising or consisting of the following layers: top layer L4, intermediate layer L3, intermediate layer L2, and bottom layer L1, and wherein layers L4 to L1 comprise the components defined in one of Tables I, Ib, II, III, and IV herein.

[0469]

[0106] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0105] , containing 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 to 99.5 wt%, 90 to 99.5 wt%, 95 to 99.0 wt%, or 97 to 98.5 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0470]

[0107] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0106] , comprising a combined weight 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 90 to 99.8 wt%, 95 to 99.5 wt%, 98 to 99.2 wt% zirconia, yttria, and hafnium dioxide, based on the total weight of the pre-sintered multilayer dental mill blank.

[0471]

[0108] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0107] , containing aluminum oxide in an amount 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 to 0.4 wt%, 0.02 to 0.2 wt%, or 0.05 to 0.1 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0472]

[0109] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0108] , which is pre-shaded and optionally contains 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 to 1.5 wt%, in the range of 0.02 to 1.0 wt%, or in the range of 0.05 to 0.8 wt%, of a coloring metal oxide, based on the total weight of the pre-sintered multilayer dental mill blank.

[0473]

[0110] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0109] , containing a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof) in a weight amount 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 to 0.8 wt%, 0.05 to 0.45 wt%, 0.10 to 0.30 wt%, or 0.15 to 0.25 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0474]

[0111] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0110] , containing a sintering inhibitor (e.g., type II yttria, optionally combined with erbium oxide) in a weight amount 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 the range of 0.1 to 2.5 wt%, 0.2 to 2.0 wt%, 0.3 to 1.5 wt%, or 0.5 to 1.2 wt%, based on the total weight of the pre-sintered multilayer dental mill blank.

[0475]

[0112] Based on the total weight of the pre-sintered multilayer dental mill blank, 80-95 wt% zirconia, for example in the range of 85-93 wt%, e.g., in the range of 89-91 wt%, hafnium oxide, e.g., 5 wt% or less, e.g., 3 wt% or less, e.g., in the range 0.5-3.0 wt%, 5.0-10.0 wt% yttria, for example in the range of 6.0-9.0 wt%, for example in the range of 6.5-8.5 wt%; 0.4 wt% or less of aluminum oxide, for example in the range of 0.02-0.2 wt%, for example in the range of 0.05-0.1 wt%, 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.0 wt %, for example in the range of 0.05 to 0.8 wt %; 0.02-0.8 wt%, 0.05-0.45 wt%, 0.10-0.30 wt% of a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof);

[0111] The pre-sintered multilayer dental mill blank according to any one of items [1] to

[0111] , wherein the weights of the components are optionally selected to total 100 wt%.

[0476]

[0113] The method is characterized by providing a representative test section for each layer, and when the representative test section of the top layer and the representative test section of the bottom layer are fully sintered by a rapid sintering process, each has a maximum sintering rate at a temperature T of the rapid sintering process, and the temperature T(T) of the top layer is TL ) and the temperature T(T BL ) differ by no more than 40°C or no more than 25°C, and optionally, when the representative test section of each layer is fully sintered by a rapid sintering process, the representative test section of each layer has a maximum sintering rate at a temperature T of the rapid sintering process, and the temperatures T of each of the layers differ by no more than 40°C or no more than 25°C.

[0477]

[0114] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0113] , characterized by providing a test section for the top layer, wherein the representative test section of the top layer, when fully sintered by a rapid sintering process, has a bending 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 to 1100 MPa, 550 to 1000 MPa, 575 to 800 MPa, or 600 to 750 MPa.

[0478]

[0115] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0114] , characterized by providing a test section for the bottom layer, wherein the representative test section of the bottom layer, when fully sintered by a rapid sintering process, has a bending 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 to 1500 MPa, in the range of 1000 to 1300 MPa, or in the range of 1050 to 1200 MPa.

[0479]

[0116] characterized by providing a test section for the top layer, wherein the representative test section of the top layer has a thermal conductivity of at least 2.5 MPa*m when fully sintered by a rapid sintering process. 1 / 2 , at least 2.7MPa*m 1 / 2 , at least 2.8MPa*m 1 / 2 , maximum 3.5MPa*m 1 / 2 , maximum 3.3MPa*m 1 / 2 , or up to 3.2MPa*m 1 / 2 , or 2.5 to 3.5 MPa*m 1 / 2 , 2.7~3.3MPa*m 1 / 2 , or 2.8 to 3.2 MPa*m 1 / 2 Fracture toughness in the range of K IC The pre-sintered multilayer dental mill blank according to any one of items [1] to

[0115] ,

[0480]

[0117] characterized by providing a test section for the bottom layer, wherein the representative test section of the bottom layer has a thermal conductivity of at least 3.6 MPa*m when fully sintered by a rapid sintering process. 1 / 2 , at least 3.8MPa*m 1 / 2 , at least 4.0MPa*m 1 / 2 , maximum 5.5MPa*m 1 / 2 , maximum 4.8MPa*m 1 / 2 , maximum 4.6MPa*m 1 / 2 , or up to 4.4MPa*m1 / 2 , or 3.6 to 5.5 MPa*m 1 / 2 , 3.8~4.8MPa*m 1 / 2 , 4.0~4.6MPa*m 1 / 2 , or 4.0 to 4.4 MPa*m 1 / 2 Fracture toughness in the range of K IC The pre-sintered multilayer dental mill blank according to any one of items [1] to

[0116] ,

[0481]

[0118] A composite material including or consisting of a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1, wherein said representative test section of said layers, when fully sintered by a rapid sintering process, exhibits a fracture toughness K IC: The top layer L4 has a compressive strength of 2.5 to 3.5 MPa*m when measured using a load of 2.5 kg. / 2. 2.7~3.3MPa*m1 / 2 , or 2.8 to 3.2 MPa*m 1 / 2 range, The intermediate layer L3 has a compressive strength of 2.6 to 3.6 MPa*m when measured using a load of 5 kg. 1 / 2 , 2.8~3.4MPa*m 1 / 2 , or 2.9 to 3.3 MPa*m 1 / 2 range, The intermediate layer L2 has a compressive strength of 3.1 to 4.2 MPa*m when measured using a load of 5 kg. 1 / 2 , 3.3~4.0MPa*m 1 / 2 , or 3.4 to 3.8 MPa*m 1 / 2 range, The bottom layer has a compressive strength of 3.6 to 4.8 MPa*m when measured using a 10 kg load. 1 / 2 , 3.8~4.6MPa*m 1 / 2 , or 3.9 to 4.4 MPa*m 1 / 2 The pre-sintered multilayer dental mill blank according to any one of items [1] to

[0117] , which may have a range of

[0482]

[0119] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0118] , wherein the rapid sintering process is a sintering process in which the total sintering time is less than 25 minutes and the maximum sintering temperature is in the range of 1350°C to 1650°C.

[0483]

[0120] The rapid sintering process comprises the following steps: a first heating step starting at -25°C and ending at 1050°C with a heating rate of 200 K / min; a second heating step starting at -1050°C and ending at 1450°C with a heating rate of 100 K / min; - a holding step of maintaining the temperature of 1450°C for 2 minutes; a first cooling step starting at -1450°C and ending at 1350°C with a cooling rate of 130 K / min; a second cooling step starting at -1350°C and ending at 1200°C with a cooling rate of 70 K / min, said second cooling step being followed by a subsequent cool down; and The pre-sintered multilayer dental mill blank according to any one of items [1] to

[0119] , wherein the first heating step and the second heating step are carried out at a pressure in the range of 50 to 100 mbar (e.g., 80 mbar) by applying a vacuum until a temperature of 1400°C is reached, and the vacuum is replaced with air when the temperature of 1400°C is reached.

[0484]

[0121] comprising at least two intermediate layers; and Optionally, the pre-sintered multilayer dental mill blank according to any one of items [1] to

[0120] is composed of a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1.

[0485] the bottom layer has a height of at least 30%, at least 40%, at least 45%, at least 50%, or at least 52% of 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% of the total height of the pre-sintered multi-layer dental mill blank; Alternatively, 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% of the total height of the pre-sintered multilayer dental mill blank according to any one of items [1] to

[0121] .

[0486] 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% of the total height of the pre-sintered multi-layer dental mill blank; or The pre-sintered multilayer dental mill blank according to any one of items [1] to

[0122] , wherein the top layer has a height of at least 8%, at least 10%, at least 12%, at least 15%, or at least 17% of the total height of the pre-sintered multilayer dental mill blank, and / or the top layer has a height of at most 35%, at most 30%, at most 28%, at most 25%, or at most 23% of the total height of the pre-sintered multilayer dental mill blank.

[0487]

[0124] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0123] , 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% of the total height of the pre-sintered multilayer dental mill blank, and / or the combined intermediate layers have a height in the range of 5 to 40%, 10 to 30%, 14 to 26% or 16 to 25% of the total height of the pre-sintered multilayer dental mill blank.

[0488]

[0125] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0124] , having a density in the range of at least 45%, at least 50%, at least 52%, at most 70%, at most 60%, at most 55%, for example 45-70%, 50-60%, or 52-55%, relative to the theoretical density of the pre-sintered multilayer dental mill blank.

[0489]

[0126] A pre-sintered multilayer dental mill blank described in any one of items [1] to

[0125] , which can be obtained by pre-sintering an unsintered body of the pre-sintered multilayer 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, at most 1100°C, at most 1000°C, at most 950°C, or at most 900°C, for example, in the range of 700 to 1100°C, 750 to 1000°C, 800 to 950°C, or 825 to 900°C.

[0490]

[0127] A pre-sintered multilayer dental mill blank obtained by the process described in any one of items

[0128] to

[0147] .

[0491] A process for preparing a presintered multilayer dental mill blank, said process comprising: a) providing three yttria-stabilized zirconia powders P1 to P3, wherein the powder P1 has an yttria content in the range of 4.5 to 6.1 wt%, the powder P2 has an yttria content in the range of 6.2 to 7.9 wt%, and the powder P3 has an yttria content in the range of 8.0 to 11.0 wt%; b) preparing a green body, a top powder layer of powder P3; at least one intermediate powder layer of a powder mixture selected from the mixture of powders P2 / P3 and the 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 the pre-sintered multi-layer dental mill blank.

[0492]

[0129] The green body is a top powder layer of powder P3; an intermediate powder layer of the mixture of powders P2 / P3; an intermediate powder layer of the mixture of powders P1 / P2, The process described in item

[0128] , which comprises or consists of a bottom powder layer of powder P1.

[0493]

[0130] A process described in any one of items

[0128] and

[0129] , wherein the yttria content of powder P1 and powder 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 to 3.0 percentage points, in the range of 1.0 to 2.8 percentage points, or in the range of 1.2 to 2.5 percentage points, and the yttria content of powder P2 and powder 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 to 3.0 percentage points, in the range of 1.0 to 2.8 percentage points, or in the range of 1.2 to 2.5 percentage points.

[0494]

[0131] A process described in any one of items

[0128] to

[0130] , wherein powder P1 has an yttria content in the range of 4.9 to 6.0 wt%, or powder P2 has an yttria content in the range of 6.5 to 7.6 wt%, or powder P3 has an yttria content in the range of 9.0 to 10.5 wt%, optionally, powder P1 has an yttria content in the range of 4.9 to 6.0 wt%, powder P2 has an yttria content in the range of 6.5 to 7.6 wt%, and powder P3 has an yttria content in the range of 9.0 to 10.5 wt%.

[0495] the mixture of powders P2 / P3 contains powders P2 and P3 in a weight ratio of 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 133. The process according to any one of items 128 to 132, wherein the mixture of powders P1 / P2 contains powders P1 and P2 in a weight ratio of 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.

[0496]

[0133] A process described in any one of items 128 to 133, wherein the process comprises adding one or more additives selected from the group consisting of sintering inhibitor precursors, sintering inhibitor precursors, and color additives to powders P1 to P3 or the mixture thereof.

[0497]

[0134] The process described in item

[0120] , wherein the one or more additives are added to the powders P1 to P3 before preparing the powder mixtures of the powders P1 / P2 and P2 / P3.

[0498]

[0135] A process described in any one of items

[0128] to

[0134] , comprising adding a sintering promoter precursor to at least powder P3 or a mixture thereof, and optionally to powders P1 to P3 or to the mixture thereof.

[0499]

[0136] The process described in item

[0135] , wherein the top powder layer has a weight content of the sintering accelerator precursor that is greater than the weight content of the sintering accelerator precursor in the bottom layer, and optionally, the weight content of the sintering accelerator precursor increases from the bottom powder layer to the top powder layer.

[0500]

[0137] The process described in any one of items

[0135] and

[0136] , wherein the sintering promoter precursor is a zinc salt, a gallium salt, or a combination thereof.

[0501]

[0138] The process comprises adding a sintering inhibitor precursor to at least the powder P1 or the mixture, The process according to any one of items

[0128] to

[0137] , optionally comprising adding to the powder P1 and the powder P2 or the mixture thereof.

[0502]

[0139] The process described in item

[0138] , wherein the bottom powder layer has a weight content of the sintering inhibitor precursor that is greater than the weight content of the sintering inhibitor precursor in the top layer, and optionally, the weight content of the sintering inhibitor precursor decreases from the bottom powder layer to the top powder layer.

[0503]

[0140] A process described in any one of items

[0138] and

[0139] , wherein the sintering inhibitor precursor is an yttrium salt, an erbium salt, a lanthanum salt, an ytterbium salt, a thulium salt, or any combination thereof, and optionally, the sintering inhibitor precursor is an yttrium salt, an erbium salt, a lanthanum salt, or any combination thereof, and optionally, the sintering inhibitor precursor is an yttrium salt, an erbium salt, or any combination thereof.

[0504]

[0141] The process of any one of items

[0138] to

[0140] , wherein the sintering inhibitor precursor is an yttrium salt, optionally in combination with an erbium salt.

[0505]

[0142] A process described in any one of items

[0128] to

[0141] , wherein the process does not include adding an yttrium salt to the powder P3.

[0506]

[0143] The process described in any one of items

[0128] to

[0142] , wherein the process comprises adding a color additive to the powder P1 to the powder P3 or the mixture thereof.

[0507]

[0144] The process described in item

[0143] , wherein the color additive comprises an erbium compound and an iron compound.

[0508]

[0145] A process described in any one of items

[0128] to

[0144] , wherein the preparation of the green body optionally includes compressing (e.g., pressing) the powder layer at a pressure in the range of 200 to 400 MPa, for example, at a pressure in the range of 250 to 350 MPa.

[0509]

[0146] A process described in any one of items

[0128] to

[0145] , wherein the preliminary sintering is at 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 within the range of 700 to 1100°C, within the range of 750 to 1000°C, within the range of 800 to 950°C, or within the range of 825 to 900°C.

[0510]

[0147] A process described in any one of items

[0128] to

[0146] , which is a process for preparing a pre-sintered multilayer dental mill blank described in any one of items [1] to

[0126] .

[0511] A process for preparing a dental restoration, said process comprising: - machining the pre-sintered multilayer dental mill blank according to any one of items [1] to

[0127] to provide a dental restoration precursor; - optionally surface treating said dental restoration precursor; - sintering the dental restoration precursor to provide the dental restoration.

[0512]

[0149] The process described in item

[0148] , wherein the machining is performed using a CAD / CAM process.

[0513]

[0150] A dental restoration obtainable by the process for preparing a dental restoration described in item

[0148] or

[0149] .

[0514] A process for sintering a dental restoration precursor, comprising: the process has a total sintering time of less than 25 minutes and a maximum sintering temperature in the range of 1350°C to 1650°C; The process comprises: (i) heat treatment; (ii) a cooling treatment, The cooling treatment includes a cooling step A, 10. A process for sintering the dental restoration precursor, wherein the cooling step A starts and ends within a temperature range between 1100°C and the maximum sintering temperature and has a cooling rate A of at least 75 K / min.

[0515]

[0152] The process described in item

[0151] , wherein the total sintering time is less than 20 minutes, less than 18 minutes, less than 16 minutes, or less than 15 minutes, for example, in the range of 5 to less than 20 minutes, 8 to less than 18 minutes, 10 to less than 16 minutes, or 12 to less than 15 minutes.

[0516]

[0153] The process according to item

[0151] or

[0152] , wherein the maximum sintering temperature is in the range of 1400 to 1600°C, in the range of 1400 to 1560°C, in the range of 1400 to 1500°C, or in the range of 1425 to 1475°C.

[0517]

[0154] A process described in any one of items

[0151] to

[0153] , wherein 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 to 250 K / min, in the range of 110 to 180 K / min, or in the range of 120 to 160 K / min.

[0518]

[0155] A process described in any one of items

[0151] to

[0154] , wherein the cooling step A starts and ends in a temperature range between 1200°C and the maximum sintering temperature, or a temperature range between 1250°C and the maximum sintering temperature, or a temperature range between 1300°C and the maximum sintering temperature.

[0519]

[0156] A process described in any one of items

[0151] to

[0155] , wherein 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.

[0520]

[0157] The process described in item

[0156] , 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 to 110 K / min, in the range of 50 to 90 K / min, or in the range of 60 to 80 K / min.

[0521]

[0158] A process described in any one of items

[0156] and

[0157] , wherein the cooling step B starts and ends in a temperature range between 1000°C and the end temperature of the cooling step A, or in a temperature range between 1100°C and the end temperature of the cooling step A, or in a temperature range between 1150°C and the end temperature of the cooling step A, or in a temperature range between 1200°C and the end temperature of the cooling step A.

[0522]

[0159] The process described in any one of items

[0151] to

[0158] , wherein the cooling treatment includes a cooling step C after the cooling step A or after the cooling step B, and the cooling step C has a cooling rate C of up to 20 K / min, up to 10 K / min, up to 5 K / min, or about 0 K / min (i.e., the cooling step C is a holding step).

[0523]

[0160] A process described in any one of items

[0151] to

[0159] , wherein the cooling treatment is completed at a final temperature followed by a cool down, 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 to 1300°C, in the range of 1100 to 1280°C, or in the range of 1150 to 1250°C.

[0524]

[0161] A process described in any one of items

[0151] to

[0160] , wherein the heat treatment 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, at most 220 K / min, in the range of 150 to 300 K / min, in the range of 170 to 250 K / min, or in the range of 190 to 220 K / min.

[0525]

[0162] The process described in item

[0161] , wherein the heat treatment includes a heating step B after the heating step A, and the heating step B has 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 to 200 K / min, in the range of 70 to 150 K / min, or in the range of 90 to 120 K / min.

[0526]

[0163] A process described in any one of items

[0151] to

[0162] , wherein the heat treatment includes a heating step C carried out at the maximum sintering temperature and at a heating rate of about 0 K / min (i.e., heating step C is a holding step at the maximum sintering temperature), and optionally the maximum sintering temperature is held in 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.

[0527]

[0164] The process described in any one of items

[0151] to

[0163] , wherein the heat treatment is carried out at least in part at a pressure of 500 mbar or less, 200 mbar or less, 150 mbar or less, or 100 mbar or less, in the range of 0.1 to 500 mbar, in the range of 1 to 200 mbar, in the range of 10 to 150 mbar, or in the range of 50 to 100 mbar.

[0528]

[0165] A process described in any one of items

[0151] to

[0164] , wherein the dental restoration precursor is pre-sintered and / or has a density in the range of at least 45%, at least 50%, at least 52%, at most 70%, at most 60%, at most 55%, for example 45-70%, 50-60%, or 52-55%, relative to its theoretical density.

[0529]

[0166] A process described in any one of items

[0151] to

[0165] , wherein the dental restoration precursor comprises zirconia and yttria, and optionally the dental restoration precursor comprises at least three sections, each section comprising zirconia and yttria, and each section having a different yttria content.

[0530]

[0167] A process described in any one of items

[0151] to

[0166] , wherein the dental restoration precursor comprises a colored oxide, and optionally, the colored oxide comprises iron oxide.

[0531]

[0168] A process described in any one of items

[0151] to

[0167] , wherein the dental restoration precursor is prepared from a pre-sintered multilayer dental mill blank, which is optionally pre-shaded.

[0532]

[0169] The process described in item

[0168] , wherein the pre-sintered multilayer dental mill blank comprises a top layer, a bottom layer, and at least one intermediate layer, each layer comprising zirconia and yttria, and the yttria content of the layers increasing from the bottom layer to the top layer.

[0533]

[0170] A process described in any one of items

[0151] to

[0169] , wherein the dental restoration precursor is prepared from a pre-sintered multilayer dental mill blank described in any one of items [1] to

[0127] .

[0534]

[0171] A dental oven configured to carry out the process described in any one of items

[0151] to

[0170] .

[0535]

[0172] A data processing device comprising means for executing the process described in any one of items

[0151] to

[0170] .

[0536]

[0173] A computer program that stores or includes commands that, when executed by a computer, cause the computer to perform a process described in any one of items

[0151] to

[0170] .

[0537]

[0174] A computer-readable medium that stores or includes instructions that, when executed by a computer, cause the computer to perform the process described in any one of items

[0151] to

[0170] .

[0538] [1b] A pre-sintered multi-layer dental mill blank comprising a top layer, a bottom layer, and at least one intermediate layer, characterized by providing a representative test section for each layer, the representative test section having a contrast ratio that increases layer by layer from the top layer to the bottom layer when fully sintered by a rapid sintering process.

[0539] [2b] The pre-sintered multilayer dental mill blank according to item [1b], wherein the contrast ratio [%] of the bottom layer differs from the contrast ratio [%] of the top layer by at least 5 percentage points when determined with a test specimen thickness of 0.8 mm.

[0540] [3b] A pre-sintered multi-layer dental mill blank comprising a top layer, a bottom layer, and at least one intermediate layer, characterized by providing representative test sections for each layer, the representative test sections having CIE L* lightness that increases layer by layer from the bottom layer to the top layer when fully sintered by a rapid sintering process.

[0541] [4b] The pre-sintered multilayer dental mill blank according to any one of items [1b] to [3b], wherein each layer comprises zirconia and yttria, and the yttria content of the layers increases from the bottom layer to the top layer.

[0542] [5b] A pre-sintered multi-layer dental mill blank comprising a top layer, a bottom layer, and at least one intermediate layer, each layer comprising zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer, characterized by providing a representative test section for each layer, wherein the representative test section of the top layer and / or the representative test section of an intermediate layer adjacent to the top layer, when fully sintered by a rapid sintering process, has a number of pores per grain of less than 0.25.

[0543] [6b] The pre-sintered multilayer dental mill blank according to any one of items [1b] to [5b], wherein the rapid sintering process is a sintering process in which the total sintering time is less than 25 minutes and the maximum sintering temperature is in the range of 1350°C to 1650°C.

[0544] [7b] The rapid sintering process comprises the steps of: a first heating step starting at -25°C and ending at 1050°C with a heating rate of 200 K / min; a second heating step starting at -1050°C and ending at 1450°C with a heating rate of 100 K / min; a holding step of maintaining said temperature at -1450°C for 2 minutes; a first cooling step starting at -1450°C and ending at 1350°C with a cooling rate of 130 K / min; a second cooling step starting at -1350°C and ending at 1200°C with a cooling rate of 70 K / min, said second cooling step being followed by a subsequent cool down; and The pre-sintered multilayer dental mill blank according to any one of items [1b] to [6b], wherein the first heating step and the second heating step are carried out at a pressure in the range of 50 to 100 mbar by applying a vacuum until a temperature of 1400°C is reached, at which point the vacuum is replaced with air.

[0545] [8b] A pre-sintered multi-layer dental mill blank comprising a top layer, a bottom layer, and at least one intermediate layer, each layer comprising zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer, and the top layer comprising a sintering aid that is zinc oxide, gallium oxide, or a combination thereof.

[0546] [9b] A pre-sintered multi-layer dental mill blank comprising a top layer, a bottom layer, and at least one intermediate layer, each layer comprising zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer, and the top layer comprising aluminum oxide in an amount of less than 0.01 wt %, based on the total weight of the top layer.

[0547] [10b] The pre-sintered multilayer dental mill blank according to any one of items [1b] to [9b], wherein each layer contains a sintering promoter such as zinc oxide, gallium oxide, or a combination thereof.

[0548] [11b] A pre-sintered multilayer dental mill blank according to any one of items [1b] to [10b], wherein the bottom layer contains yttria as a sintering inhibitor, and the yttria is obtained by converting a yttrium salt as a sintering inhibitor precursor into the sintering inhibitor when pre-sintering the green body of the multilayer dental mill blank.

[0549] [12b] The pre-sintered multilayer dental mill blank according to any one of items [1b] to [11b], wherein the top layer contains yttria in an amount ranging from 9.0 to 12.0 wt %, based on the total weight of the top layer, and the bottom layer contains yttria in an amount ranging from 5.5 to 7.5 wt %, based on the total weight of the bottom layer.

[0550] [13b] A pre-sintered multilayer dental mill blank according to any one of items [1b] to [12b], comprising at least two intermediate layers.

[0551] [14b] The pre-sintered multilayer dental mill blank according to any one of items [1b] to [13b], comprising: a top layer L4 obtained from an yttria-stabilized zirconia powder P3; an intermediate layer L3 obtained from a mixture of an yttria-stabilized zirconia powder P2 and the powder P3; an intermediate layer L2 obtained from a mixture of an yttria-stabilized zirconia powder P1 and the powder P2; and a bottom layer L1 obtained from an yttria-stabilized zirconia powder P1, wherein the powder P1 has an yttria content in the range of 4.5 to 6.1 wt%, the powder P2 has an yttria content in the range of 6.2 to 7.9 wt%, and the powder P3 has an yttria content in the range of 8.0 to 11.0 wt%.

[0552] [15b] A pre-sintered multilayer dental mill blank according to any one of items [1b] to [14b], which is pre-shaded.

[0553] [16b] A pre-sintered multilayer dental mill blank according to any one of items [1b] to [15b], which is composed of a top layer L4, an intermediate layer L3, an intermediate layer L2, and a bottom layer L1, and wherein the layers L4 to L1 contain the components defined in Table Ib, the weights indicated here being based on the total weight of the respective layers. [Table 19]

[0554] [17b] A process for preparing a presintered multilayer dental mill blank, said process comprising: a) providing three yttria-stabilized zirconia powders P1 to P3, wherein the powder P1 has an yttria content in the range of 4.5 to 6.1 wt%, the powder P2 has an yttria content in the range of 6.2 to 7.9 wt%, and the powder P3 has an yttria content in the range of 8.0 to 11.0 wt%; b) preparing a green body, a top powder layer of powder P3; at least one intermediate powder layer of a powder mixture selected from the mixture of powders P2 / P3 and the mixture of powders P1 / P2, preparing the green body, which is composed of a bottom powder layer of powder P1 or a mixture of powders P1 / P2; c) pre-sintering the green body to provide the pre-sintered multi-layer dental mill blank.

[0555] [18b] The process according to item [17b], wherein the green body is composed of a top powder layer of powder P3, a middle powder layer of the mixture of powders P2 / P3, a middle powder layer of the mixture of powders P1 / P2, and a bottom powder layer of powder P1.

[0556] [19b] The process according to item [17b] or [18b], wherein the mixture of powders P2 / P3 contains powders P2 and P3 in a weight ratio of powder P2:powder P3 ranging from 10:90 to 40:60, from 15:85 to 35:65, or from 20:80 to 30:70, or the mixture of powders P1 / P2 contains powders P1 and P2 in a weight ratio of powder P1:powder P2 ranging from 10:90 to 40:60, from 15:85 to 35:65, or from 20:80 to 30:70.

[0557] [20b] The process according to any one of Items [17b] to [19b], comprising adding a sintering accelerator precursor to the powders P1 to P3 or the mixture thereof, wherein the sintering accelerator precursor is a zinc salt, a gallium salt, or a combination thereof.

[0558] [21b] The process according to any one of Items [17b] to [20b], comprising adding a sintering inhibitor precursor to the powder P1 and the powder P2 or the mixture thereof, wherein the sintering inhibitor precursor is an yttrium salt.

[0559] [22b] A process for preparing a dental restoration, said process comprising: - machining the pre-sintered multilayer dental mill blank according to any one of items [1] to [16b] to provide a dental restoration precursor, - optionally surface treating said dental restoration precursor, - sintering said dental restoration precursor to provide said dental restoration.

[0560] [23b] A dental restoration obtained by the process for preparing a dental restoration according to item [22b].

[0561] [24b] A process for sintering a dental restoration precursor, comprising: the process has a total sintering time of less than 25 minutes and a maximum sintering temperature in the range of 1350°C to 1650°C; The process comprises: (i) heat treatment; (ii) a cooling treatment, 1. A process for sintering the dental restoration precursor, wherein the cooling treatment comprises a cooling step A, which starts and ends within a temperature range between 1100°C and the maximum sintering temperature, and which has a cooling rate A of at least 75 K / min.

[0562] [25b] The process according to item [24b], wherein the cooling step A starts 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.

[0563] [26b] The process according to item [24b] or [25b], wherein the cooling treatment comprises 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.

[0564] [27b] The process according to any one of items [24b] to [26b], wherein the heat treatment is carried out partially at a pressure of 500 mbar or less.

[0565] [28b] A process The process according to any one of items [24b] to [27b], wherein the heat treatment comprises a heating step A with a heating rate A of at least 170 K / min and a heating step B following the heating step A, wherein the heating step B has a heating rate B of at least 70 K / min, which is lower than the heating rate A.

[0566] [29b] The process according to any one of items [24b] to [28b], wherein the dental restoration precursor comprises at least three sections, each section comprising zirconia and yttria, and each section having a different yttria content.

[0567] VI. Working Examples Section 1.Measurement method 1.1 Contrast Ratio (CR) and Color (CIE L*, a*, b*) Contrast ratio (CR) was measured in accordance with BS5612 (BS5612:1978) on test specimens with a thickness of 0.80 mm (±0.02 mm). Color (CIE L*, a*, b*) was measured in accordance with DIN6174 on test specimens with a thickness of 0.80 mm (±0.02 mm). Color (CIE L*, a*, b*) was measured on the following backgrounds: L* = 93.1, a* = (-0.64), b* = 4.22. Measurements were performed using a spectrophotometer CM3700-D (Konica-Minolta). Prior to measurement, the test specimens were wet polished to a thickness of 0.80 mm (±0.02 mm) using a rotary diamond polishing disc and 1000 SiC polishing paper, followed by wet polishing of the final surface using a diamond polishing disc (20 μm).

[0568] 1.2 Flexural strength and fracture toughness Flexural strength may be determined in accordance with ISO 6872:2015.

[0569] Fracture toughness (K Ic ) were determined according to the experimental conditions and the procedures described in Chapters 5, 6, and 7 of ISO 14627, and calculated using Shinhara's formula for palmquist cracks. The indentation loads of the Vickers indenter were 2.5-5 kg ​​(top layer), 2.5-10 kg (middle layer(s)), and 10-20 kg (bottom layer). The Vickers indentation loads for powders 1-3 were 10-20 kg (powder 1), 5-10 kg (powder 2), and 2.5-5 kg ​​(powder 3). The Shinhara formula for palmquist cracks is as follows:

number

number

[0570] 1.3 Number of pores per grain The number of pores per grain (including the number of intragranular pores per grain) was determined according to the following test protocol: - The surface of the fully sintered representative test section is subjected to a surface polishing sequence using a series of surface polishing steps (1) to (3): (1) 20 μm diamond surface polishing, (2) surface polishing with surface polishing tools (e.g., Apex surface polishing tools) of sizes 70, 15, 6, and 0.5 μm, (3) surface polishing with nanosilica dispersion (e.g., for 2 minutes) and rinsing with water (e.g., for 2 minutes); -Preparing images of surface-polished surfaces by scanning electron microscope (SEM); - Use image analysis software (e.g., Olympus software) to select a surface area (herein also referred to as ROI, i.e., region of interest) on the SEM image: the ROI should be at least 50 µm (e.g., between 50 and 2000 µm 2 Range: 50~1500μm 2 Range: 50~1000μm 2 Range: 50~500μm 2 range, or 50 to 300 μm 2 range) and exhibiting at least 50 grains (e.g., 50-400 grains); - determining the number average particle size of the grains shown in the ROI: (1) determining a preliminary number average particle size using the line intersection method according to DIN EN 623-3 or ASTM E 112; (2) multiplying the obtained value by the proportionality constant 1.56 to obtain the number average particle size in the three-dimensional microstructure according to M.I. Mendelson, J. Am. Ceram. Soc. 1969, 52(8), 443-446 (incorporated herein by reference); -Identify and count grains and pores (including intergranular and intragranular pores) and calculate the number of pores per grain.

[0571] 2. Screening Method Screening or directional experiments to test the sintering behavior of sintering accelerators or inhibitors, raw materials and / or coloring oxides can be carried out using one continuous sintering process (i.e., without preparing a separate pre-sintered body) starting from a single layer of pressed powd...

Claims

1. 1. A presintered multilayer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; each layer comprises zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; and The pre-sintered multi-layer dental mill blank, wherein the top layer comprises a sintering promoter selected from zinc oxide, gallium oxide, or a combination thereof.

2. 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. 3. The presintered multi-layer dental mill blank of claim 1, wherein the yttria content of the layers increases from layer to layer from the bottom layer to the top layer.

4. 4. The pre-sintered multilayer dental mill blank of claim 1, 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. 1. A presintered multilayer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; each layer comprises zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; and The pre-sintered multi-layer dental mill blank, wherein the top layer comprises aluminum oxide in an amount of less than 0.01 wt %, based on the total weight of the top layer.

6. 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. 7. The presintered multi-layer dental mill blank of claim 5 or 6, wherein the yttria content of the layers increases from layer to layer from the bottom layer to the top layer.

8. 8. The pre-sintered multi-layer dental mill blank of claim 5, wherein the top layer comprises a sintering promoter selected from the group consisting of zinc oxide, gallium oxide, and a combination thereof.

9. The presintered multi-layer dental mill blank of any one of claims 1 to 8, wherein each layer comprises a sintering promoter, zinc oxide, gallium oxide, or a combination thereof.

10. 10. The pre-sintered multilayer dental mill blank according to claim 1, wherein the bottom layer contains yttria as a sintering inhibitor, and the yttria is obtained by converting a yttrium salt as a sintering inhibitor precursor into the sintering inhibitor when pre-sintering the green body of the multilayer dental mill blank.

11. The following layers: Top layer L4, middle layer L3, middle layer L2, a bottom layer L1, the top layer L4 comprises yttria in an amount ranging from 7.0 to 13.0 wt %, 8.0 to 12.0 wt %, 9.0 to 11.0 wt %, or 9.5 to 10.5 wt %, based on the total weight of the top layer; the intermediate layer (L3) comprises yttria in a weight range of 6.0 to 11.0 wt %, 7.5 to 10.5 wt %, or 8.5 to 10.0 wt %, or 9.0 to 9.5 wt %, based on the total weight of the intermediate layer (L3); the intermediate layer (L2) comprises yttria in a weight range of 4.5 to 9.0 wt %, 5.5 to 8.0 wt %, 6.0 to 7.5 wt %, or 6.5 to 7.3 wt %, based on the total weight of the intermediate layer (L2); and 11. The pre-sintered multilayer dental mill blank of claim 1, wherein the bottom layer (L1) comprises yttria in a weight range of 4.0 to 9.0 wt %, 5.0 to 8.0 wt %, 5.5 to 7.5 wt %, or 6.0 to 6.8 wt %, based on the total weight of the bottom layer (L1).

12. the top layer comprising yttria in an amount ranging from 9.0 to 12.0 wt %, based on the total weight of the top layer; 12. The pre-sintered multi-layer dental mill blank of claim 1, wherein the bottom layer comprises yttria in a weight range of 5.5 to 7.5 wt %, based on the total weight of the bottom layer.

13. a top layer L4 obtained from yttria-stabilized zirconia powder P3, an intermediate layer L3 obtained from a mixture of yttria-stabilized zirconia powder P2 and powder P3; an intermediate layer L2 obtained from a mixture of yttria-stabilized zirconia powder P1 and powder P2; a bottom layer L1 obtained from yttria-stabilized zirconia powder P1; and 13. The pre-sintered multilayer dental mill blank according to claim 1, wherein the powder P1 has an yttria content in the range of 4.5 to 6.1 wt %, the powder P2 has an yttria content in the range of 6.2 to 7.9 wt %, and the powder P3 has an yttria content in the range of 8.0 to 11.0 wt %.

14. A pre-sintered multilayer dental mill blank according to any one of claims 1 to 13, which is pre-shaded.

15. The top layer comprises, based on the total weight of the top layer: 80-92 wt% zirconia, for example in the range of 85-91 wt%, for example in the range of 87-90 wt%, Hafnium dioxide, e.g., 3.0 wt % or less, e.g., in the range of 0.5 to 3.0 wt %, 5.0 wt % or less; 7.0-13.0 wt. % yttria, for example in the range of 8.0-12.0 wt. %, for example in the range of 9.0-11.0 wt. %; less than 0.01 wt. % aluminum oxide; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %, 0.02-0.80 wt % of a sintering promoter, for example, in the range of 0.02-0.50 wt %, e.g., in the range of 0.10-0.30 wt %, zinc oxide, gallium oxide, or a combination thereof; The pre-sintered multilayer dental mill blank according to any one of claims 1 to 14, comprising:

16. The bottom layer comprises, based on the total weight of the bottom layer: 85-94 wt% zirconia, for example in the range of 88-94 wt%, for example in the range of 90-92 wt%, Hafnium dioxide, e.g., 3.0 wt % or less, e.g., in the range of 0.5 to 3.0 wt %, 5.0 wt % or less; 0.01 to 0.50 wt % aluminum oxide, for example in the range of 0.02 to 0.40 wt %, for example in the range of 0.05 to 0.20 wt %, 4.0-9.0 wt % yttria, for example in the range of 5.0-8.0 wt %, for example in the range of 5.5-7.5 wt %; 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %, 0.02-0.80 wt % of a sintering promoter, for example, in the range of 0.02-0.50 wt %, e.g., in the range of 0.05-0.30 wt %, zinc oxide, gallium oxide, or a combination thereof; The pre-sintered multilayer dental mill blank according to any one of claims 1 to 15, comprising:

17. each of the at least one intermediate layer having, based on the total weight of the respective layer of the at least one intermediate layer: 82-94 wt% zirconia, for example in the range of 85-93 wt%, for example in the range of 87-92 wt%, Hafnium dioxide, e.g., 3.0 wt % or less, e.g., in the range of 0.5 to 3.0 wt %, 5.0 wt % or less; 0.01 to 0.50 wt % aluminum oxide, for example in the range of 0.02 to 0.20 wt %, for example in the range of 0.02 to 0.15 wt %, 5.0-11.0 wt% yttria, for example in the range of 6.0-10.5 wt%, for example in the range of 6.5-10.0 wt%, 0.01 to 1.5 wt % of a coloring metal oxide, for example in the range of 0.02 to 1.2 wt %, for example in the range of 0.05 to 1.0 wt %, 0.02-0.80 wt % of a sintering promoter, for example, in the range of 0.02-0.50 wt %, e.g., in the range of 0.05-0.30 wt %, zinc oxide, gallium oxide, or a combination thereof; The pre-sintered multilayer dental mill blank according to any one of claims 1 to 16, comprising:

18. A top layer L4; an intermediate layer L3; an intermediate layer L2; a bottom layer L1; 18. The pre-sintered multilayer dental mill blank according to claim 1, wherein layers L4 to L1 comprise the components defined in Table lb, the weights indicated here being based on the total weight of the respective layers. Table 1

19. 1. A presintered multilayer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; characterizing the presintered multi-layer dental mill blank by providing a representative test section for each layer; The pre-sintered multi-layer dental mill blank, wherein the representative test section has a contrast ratio that increases from the top layer to the bottom layer when fully sintered by a rapid sintering process.

20. 20. The pre-sintered multilayer dental mill blank of claim 19, wherein the contrast ratio increases from the top layer to the bottom layer such that the contrast ratio of the top layer is lower than the contrast ratio of the at least one intermediate layer, and the contrast ratio of the at least one intermediate layer is lower than the contrast ratio of the bottom layer.

21. 21. The pre-sintered multi-layer dental mill blank of claim 19 or 20, wherein the contrast ratio increases from layer to layer going from the top layer to the bottom layer.

22. 22. The pre-sintered multilayer dental mill blank of claim 19, wherein the contrast ratio [%] of the bottom layer differs from the contrast ratio [%] of the top layer by at least 5 percentage points when determined on a test specimen thickness of 0.8 mm.

23. 23. The pre-sintered multilayer dental mill blank according to any one of claims 19 to 22, comprising the following layers: a top layer L4, an intermediate layer L3, an intermediate layer L2, a bottom layer L1, and wherein the contrast ratios of the layers satisfy one or more of the contrast ratio profiles A1.1 to J1.1 defined in Table A1. Table 2

24. 1. A presintered multilayer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; characterizing the presintered multi-layer dental mill blank by providing a representative test section for each layer; The presintered multi-layer dental mill blank, wherein the representative test section has a CIE L* lightness that increases from the bottom layer to the top layer when fully sintered by a rapid sintering process.

25. 25. The pre-sintered multilayer dental mill blank of claim 24, wherein the CIE L* color values ​​increase from the bottom layer to the top layer such that the CIE L* color value of the bottom layer is lower than the CIE L* color value of the at least one intermediate layer, and the CIE L* color value of the at least one intermediate layer is lower than the CIE L* color value of the bottom layer.

26. 26. The pre-sintered multi-layer dental mill blank of claim 24 or 25, wherein the CIE L* color value increases from layer to layer from the top layer to the bottom layer.

27. 27. The pre-sintered multi-layer dental mill blank of claim 19, wherein each layer comprises zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer.

28. 28. The pre-sintered multi-layer dental mill blank of claim 27, wherein the yttria content of the layers increases from the bottom layer to the 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. 29. The pre-sintered multi-layer dental mill blank of claim 27 or 28, wherein the yttria content of the layers increases from layer to layer from the bottom layer to the top layer.

30. 1. A presintered multilayer dental mill blank, comprising: The top layer and A bottom layer; at least one intermediate layer; each layer comprising zirconia and yttria, the yttria content of the layers increasing from the bottom layer to the top layer; The presintered multi-layer dental mill blank is characterized by providing a representative test section for each layer; and The pre-sintered multilayer dental mill blank, wherein the representative test section of the top layer and / or an intermediate layer adjacent to the top layer has a number of intragranular pores per grain of less than 0.25 when fully sintered by a rapid sintering process.

31. 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. 32. The presintered multi-layer dental mill blank of claim 30 or 31, wherein the yttria content of the layers increases from layer to layer from the bottom layer to the top layer.

33. each layer comprising zirconia and yttria, the yttria content of the layers preferably increasing from the bottom layer to the top layer; each layer includes a sintering promoter (e.g., zinc oxide, gallium oxide, or a combination thereof); Optionally, each layer comprises a colored metal oxide; and 33. The pre-sintered multilayer dental mill blank of any one of claims 20 to 32, wherein the bottom layer and, optionally, each of the at least one intermediate layer comprises a sintering inhibitor (e.g., type II yttria).

34. 34. The pre-sintered multilayer dental mill blank of 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. 35. The pre-sintered multi-layer dental mill blank of any one of claims 27 to 34, wherein each layer comprises a sintering promoter, zinc oxide, gallium oxide, or a combination thereof.

36. 36. The pre-sintered multilayer dental mill blank according to claim 27, wherein the bottom layer contains yttria as a sintering inhibitor, and the yttria is obtained by converting a yttrium salt as a sintering inhibitor precursor into the sintering inhibitor when pre-sintering the green body of the multilayer dental mill blank.

37. the top layer comprising yttria in an amount ranging from 9.0 to 12.0 wt %, based on the total weight of the top layer; 37. The pre-sintered multilayer dental mill blank of any one of claims 27 to 36, wherein the bottom layer comprises yttria in a weight range of 5.5 to 7.5 wt %, based on the total weight of the bottom layer.

38. a top layer L4 obtained from yttria-stabilized zirconia powder P3; an intermediate layer L3 obtained from a mixture of yttria-stabilized zirconia powder P2 and powder P3; an intermediate layer L2 obtained from a mixture of yttria-stabilized zirconia powder P1 and powder P2; a bottom layer L1 obtained from yttria-stabilized zirconia powder P1, 38. A pre-sintered multilayer dental mill blank according to any one of claims 19 to 37, wherein powder P1 has an yttria content in the range of 4.5 to 6.1 wt%, powder P2 has an yttria content in the range of 6.2 to 7.9 wt%, and powder P3 has an yttria content in the range of 8.0 to 11.0 wt%.

39. A pre-sintered multilayer dental mill blank according to any one of claims 19 to 38, which is pre-shaded.

40. The pre-sintered multi-layer dental mill blank is characterized by providing a representative test section for each layer, and the representative test section, when fully sintered by a rapid sintering process, exhibits a fracture toughness K ＩＣ and the fracture toughness K of the top layer is characterized by ＩＣ is 2.5 to 3.5 MPa*m １／２ , 2.7~3.3MPa*m １／２ , or 2.8 to 3.2 MPa*m １／２ and the fracture toughness K of the bottom layer is in the range ＩＣ is 3.6 to 5.5 MPa*m １／２ , 3.8~4.8MPa*m １／２ , 4.0~4.6MPa*m １／２ , or 4.0 to 4.4 MPa*m １／２ 40. The pre-sintered multilayer dental mill blank according to any one of claims 19 to 39, wherein the thickness of the pre-sintered multilayer dental mill blank is in the range of 0.1 to 0.2 mm.

41. A top layer L4; an intermediate layer L3; an intermediate layer L2; a bottom layer L1; 41. The pre-sintered multilayer dental mill blank according to any one of claims 19 to 40, wherein layers L4 to L1 comprise the components defined in Table Ib, the weights indicated here being based on the total weight of the respective layers. Table 3

42. 42. The pre-sintered multilayer dental mill blank according to any one of claims 19 to 41, wherein the rapid sintering process is a sintering process having a total sintering time of less than 25 minutes and a maximum sintering temperature in the range of 1350°C to 1650°C.

43. The rapid sintering process comprises the following steps: A first heating step starting at −25° C. and ending at 1050° C. with a heating rate of 200 K / min, A second heating step starting at -1050°C and ending at 1450°C with a heating rate of 100 K / min, - a holding step of maintaining the temperature of 1450°C for 2 minutes; a first cooling step starting at −1450° C. and ending at 1350° C. with a cooling rate of 130 K / min; a second cooling step starting at -1350°C and ending at 1200°C with a cooling rate of 70 K / min, said second cooling step being followed by a subsequent cool down; and 43. The pre-sintered multilayer dental mill blank according to any one of claims 19 to 42, wherein the first and second heating steps are carried out at a pressure in the range of 50 to 100 mbar by applying a vacuum until a temperature of 1400°C is reached, at which point the vacuum is replaced with air.

44. 1. A presintered multi-layer dental mill blank comprising the following layers: A top layer L4; an intermediate layer L3; an intermediate layer L2; a bottom layer L1; The pre-sintered multi-layer dental mill blank, wherein the layers L4 to L1 comprise the components defined in Table I below, the weights shown being based on the total weight of the respective layers. Table 4

45. A pre-sintered multi-layer dental mill blank according to any one of claims 1 to 44, having attached to one or more of its outer surfaces another component or layer, such as a retaining pin, a support layer, a protective layer, a printing layer, or a sacrificial layer.

46. 1. A process for preparing a presintered multilayer dental mill blank, said process comprising: a) providing three yttria-stabilized zirconia powders P1 to P3, wherein P1 has an yttria content in the range of 4.5 to 6.1 wt %, P2 has an yttria content in the range of 6.2 to 7.9 wt %, and P3 has an yttria content in the range of 8.0 to 11.0 wt %; b) preparing a green body, a top powder layer of said powder P3; at least one intermediate powder layer of a powder mixture selected from the mixture of powders P2 / P3 and the 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 the pre-sintered multi-layer dental mill blank.

47. The green body, a top powder layer of said powder P3; an intermediate powder layer of the mixture of powders P2 / P3, an intermediate powder layer of the mixture of powders P1 / P2, 47. The process of claim 46, comprising a bottom powder layer of said powder P1.

48. the mixture of powders P2 / P3 contains powders P2 and P3 in a weight ratio of powder P2:powder P3 ranging from 10:90 to 40:60, ranging from 15:85 to 35:65, or ranging from 20:80 to 30:70, or 48. The process of claim 46 or 47, wherein the mixture of powders P1 / P2 contains powders P1 and P2 in a weight ratio of 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.

49. 49. The process of any one of claims 46 to 48, comprising adding a sintering promoter precursor to powders P1 to P3 or the mixture thereof, wherein the sintering promoter precursor is a zinc salt, a gallium salt, or a combination thereof.

50. 50. The process of any one of claims 46 to 49, comprising adding a sintering inhibitor precursor to said powder P1 and said powder P2 or said mixture thereof, wherein said sintering inhibitor precursor is an yttrium salt.

51. 1. A process for preparing a dental restoration, comprising: - machining a presintered multilayer dental mill blank according to any one of claims 1 to 45 to provide a dental restoration precursor, - optionally surface treating said dental restoration precursor, - sintering said dental restoration precursor to provide said dental restoration.

52. 52. A dental restoration obtainable by the process for preparing a dental restoration according to claim 51.

53. 1. A process for sintering a dental restoration precursor, comprising: the process has a total sintering time of less than 25 minutes and a maximum sintering temperature in the range of 1350°C to 1650°C; The process comprises: (i) a heat treatment; (ii) a cooling treatment, 1. A process for sintering the dental restoration precursor, wherein the cooling treatment comprises a cooling step A, which starts and ends within a temperature range between 1100°C and the maximum sintering temperature, and which has a cooling rate A of at least 75 K / min.

54. 54. The process of claim 53, wherein the cooling step A starts 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.

55. 55. The process of claim 53 or 54, wherein the cooling treatment comprises a cooling step B after the cooling step A, wherein the cooling step B has a lower cooling rate B than the cooling step A.

56. 56. The process of any one of claims 53 to 55, wherein the heat treatment is carried out partially at a pressure of up to 500 mbar.

57. a heating step A, wherein the heat treatment has a heating rate A of at least 170 K / min; 57. The process of any one of claims 54 to 56, comprising a heating step B subsequent to heating step A, wherein heating step B has a heating rate of at least 70 K / min and is lower than heating rate A.

58. 58. The process of any one of claims 53 to 57, wherein the dental restoration precursor comprises at least three sections, each section comprising zirconia and yttria, and each section having a different yttria content.

59. A dental oven configured to carry out the process of any one of claims 53 to 58.

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