METHOD FOR MANUFACTURING DENTAL MILLING BLOCKS HAVING HOMOGENEOUS COLOR AND / OR TRANSLUCENCE GRADIENTS - Patent application

Abstract

The present invention relates to a method for producing a dental milling block with a homogenous color and / or translucency gradient, the method comprising the steps of providing a mold having a cavity with a z-direction and an x / y-direction, and partially filling the cavity to a height H1 with a first powder, the first powder having a volume V having an upper surface and a lower surface. P1 and introducing a second powder to a height H2 above the first powder, wherein the second powder has a volume V having an upper surface and a lower surface. P2 The present invention relates to a method for producing a dental restoration using a dental milling block obtained according to this method, the method comprising the steps of: introducing a first powder having an upper surface in contact with a lower surface of a second powder to form an intermediate region; providing a mixer unit having at least one rotatable mixing element; introducing the rotating mixing element into the intermediate region in a z-direction; mixing the powders disposed in the intermediate region by rotating the mixing element; removing the rotating mixing element from the powders; compressing the powders; and optionally applying heat to the compressed powder, wherein the first powder differs from the second powder by its physical properties and / or chemical composition and / or color. The present invention also relates to a method for producing a dental restoration using a dental milling block obtained according to this method.

Description

[Technical Field]

[0001] The present invention relates to a method for producing dental milling blocks with a homogeneous color and / or translucency gradient, which can be used to produce highly aesthetic dental restorations. [Background technology]

[0002] In order to produce highly aesthetic dental restorations, it is necessary to take into account the individual colored tooth conditions in the patient's mouth.

[0003] On the other hand, to reproduce the natural appearance of teeth, dental milling blocks with color gradients are commercially available, which are milled and sintered to produce dental restorations.

[0004] Various concepts for manufacturing these types of dental milling blocks have been described in the art.

[0005] One concept focuses on the use of a coloring solution that is applied to a porous dental milling block. During the application process, the coloring ions present in the coloring solution are absorbed by the porous dental milling block, creating a color gradient.

[0006] For example, Chinese Patent No. 104909745(B) (Chengdu Besmile Biotech.) describes a preparation method for obtaining a zirconium oxide porcelain block with a uniform color gradient. The preparation method includes: (1) a mixture of CeO2, Fe2O3, ZrO2, Y2O3, Pr6O 11and Er2O3, (2) adding a polymer binder and granulating the mixture, (3) molding the granulated material, (4) performing isostatic cold pressing, (5) pre-sintering a porcelain block blank, (6) placing the pre-sintered porcelain block blank flat in a staining container and staining it under specific conditions, and (7) sintering the stained porcelain block to obtain a dental zirconium oxide porcelain block with a uniform color gradient.

[0007] Chinese Patent Publication No. 108585845(A) (Bloomden Bioceramics) describes a method for preparing zirconium oxide ceramic blanks with gradually changing color and transparency, which includes the steps of: (1) preparing a soluble yttrium solution, immersing one side of a pre-sintered zirconium oxide ceramic in the liquid level of the solution, applying negative pressure to the other side of the zirconium oxide ceramic, and controlling the rate of decrease in the liquid level according to a preset pressure-time curve until the liquid level drops to zero; and (2) preparing a custom-made 16-color dyeing solution satisfying 16 vita colors or a custom-made 26-color dyeing solution satisfying 26 vita colors, turning the dried zirconium oxide ceramic upside down 180 degrees, immersing one side of the zirconium oxide ceramic in the liquid level of the dyeing solution, applying negative pressure to the other side of the zirconium oxide ceramic, and controlling the rate of decrease in the liquid level according to a preset pressure-time curve until the liquid level drops to zero.

[0008] U.S. Patent Application Publication No. 2019 / 0233340(A1) (Kim et al.) describes a method for coloring a ceramic body for use in dental applications. The method includes obtaining a porous ceramic body including first and second end faces and a side face, contacting various portions of the ceramic body with a casing material, infiltrating a diluent to occupy the first porous region, conditioning the casing, and infiltrating a liquid coloring composition to occupy the second porous region, wherein the casing material prevents the liquid coloring composition and the diluent from penetrating the first end face and the side face.

[0009] Another concept focuses on layering powder compositions of various colors on top of each other and then compressing the powder compositions.

[0010] European Patent Publication No. 3108849(A1) (3M) relates to a porous multilayer colored zirconia dental mill blank comprising two different layers having alternating compositions B and E, the thickness of the individual layers having composition B decreasing from bottom to top and the thickness of the individual layers having composition E decreasing from top to bottom.

[0011] U.S. Patent No. 10,245,127 (B2) (Kim et al.) describes a method for producing a multilayer zirconia block for artificial teeth, which includes a first material mixing step, a second material mixing step, a third material mixing step, a compression molding step, and a sintering step. This method is believed to provide a multilayer zirconia block containing yttrium oxide, the amount of yttrium oxide being adjusted during the manufacturing process, and therefore exhibits a color similar to that of natural teeth after impregnation with a coloring solution.

[0012] Yet another concept suggests the use of a mixer to mix the powder composition.

[0013] U.S. Patent No. 10,441,391 (B2) (Volkl et al.) describes a method for producing colored zirconia blanks by mixing raw materials in powder form, pressing the resulting mixture, and then subjecting it to heat treatment. One of the powder mixtures contains a coloring substance. After the introduction of a first powder layer, another, less colored material is filled into the mold to form an intermediate layer mixed with the first layer. Subsequently, a further layer having a higher yttrium oxide content than the first layer is filled into the mold.

[0014] Additional dental milling blocks having different layers or regions are described, for example, in U.S. Patent No. 10,219,880 (Rolf et al.). The dental mill blank includes a first layer of a first hard restorative material having a first translucency and a first color shade, and a second layer of a second hard restorative material having a second translucency and a second color shade, where at least one of the following is true: (1) the first translucency is different from the second translucency; or (2) the first color shade is different from the second color shade. The first and second layers form a first interface having a first curve across a first plane of symmetry of the dental mill blank, the first curve having a non-zero curvature and a first straight line along the entire length of a second surface of the dental mill blank, the second surface being orthogonal to the first plane of symmetry.

[0015] U.S. Pat. No. 10,028,809 (A1) (Jahns et al.) relates to a porous dental milling block comprising at least two geometrically defined material sections A and B containing different amounts of tetragonal and cubic zirconia crystalline phases. Summary of the Invention

[0016] None of the methods described are entirely satisfactory, and there remains a need for alternative methods that may serve to simplify or improve existing methods.

[0017] In particular, the various layers of different powder components may still be visible.

[0018] Therefore, there is a need for dental milling blocks with a more uniform color gradient.

[0019] If possible, the method for producing such dental milling blocks should be less complicated.

[0020] In one embodiment, the present invention provides a method for producing a dental milling block, comprising the steps of: providing a mold having a cavity with an iz direction and an x / y direction; ii. Partially filling the cavity with a first powder to a height H1, wherein the first powder has a volume V having an upper surface and a lower surface. P1 a filling step comprising: iii. introducing a second powder to a height H2 above the first powder, wherein the second powder has a volume V having an upper surface and a lower surface. P2 and introducing a first powder such that an upper surface of the first powder is in contact with a lower surface of the second powder, forming an intermediate or interface region; iv. Providing a mixer unit having at least one rotatable mixing element; v. Rotating mixing elements are rotated, typically for a time t start introducing the intermediate region in the z direction; vi. By rotating the mixing element, typically for a time t mix(x,y,z) The powders placed in the intermediate region are mixed for a period of time t, thereby forming a continuous transition region by the movement of the rotating mixing element from the already mixed region to the unmixed region. mix(x’,y’,z’) continuing mixing for a period of time; vii. Typically, time t end removing the rotating mixing element from the powder; viii. compressing the powder by applying a pressure preferably between 10 MPa and 300 MPa for 0.5 seconds to 5 minutes; ix. optionally applying heat to the compacted powder, preferably by applying a heating gradient followed by a dwell temperature of 800°C to 1,100°C for 5 minutes to 300 minutes at ambient conditions; The first powder is characterized in a way that it differs from the second powder by its physical properties and / or chemical composition and / or color.

[0021] The present invention is also directed to a method for producing a dental restoration obtained by machining from the dental milling block described herein, and to a dental restoration obtained by such a method.

[0022] A further aspect of the present invention relates to a kit-of-parts comprising a mold as described herein, a mixer unit as described herein, and the first and second powders as described herein.

[0023] Unless otherwise defined, as used herein, the following terms have the meanings set forth below.

[0024] The term "dental restoration" refers to an article used in dentistry to restore missing tooth structure. Dental restorations typically have three-dimensional inner and outer surfaces. The surfaces typically include convex and concave structures. Compared to other articles, such as porcelain or paving stones, dental restorations are small and delicate. The thickness of a dental restoration can vary from very thin, e.g., at the edges and rims (less than 0.1 mm), to quite thick, e.g., in the occlusal region (up to 8 or 16 mm). The section bridging the crown portion in a dental bridge can have a thickness of up to 20 mm. The outer surface typically has an overall convex shape, while the inner surface typically has an overall concave shape.

[0025] The dental restorations described herein, after sintering, comprise or consist essentially of a polycrystalline ceramic material including yttrium-stabilized zirconia.

[0026] Examples of dental restorations include crowns (such as monolithic crowns), bridges, inlays, onlays, veneers, facings, crown and bridge frameworks, abutments, orthodontic appliances (e.g., brackets, buccal tubes, cleats and buttons), and portions thereof.

[0027] Tooth surfaces are considered not to be dental articles or dental restorations.

[0028] Dental restorations should not contain ingredients that are harmful to the patient's health and thus should be free of harmful and toxic ingredients that can migrate out of the dental restoration.

[0029] "Dental mill blank or dental milling block" means a solid block of material (a three-dimensional object) from which a dental restoration can be, and typically is, machined by subtractive processes, such as grinding, drilling, etc., in addition to milling. A dental mill blank has a geometrically defined shape and typically has two opposing flat surfaces. So-called "free-form surfaces" are not considered "geometrically defined." In this regard, the shape of a dental restoration (e.g., a crown or bridge) itself is not considered a dental mill blank.

[0030] "Zirconia article" shall mean a three-dimensional article having at least one of the x, y, z dimensions of at least about 5 mm, the article being composed of at least 80% by weight, or at least 90% by weight, or at least 95% by weight, zirconia.

[0031] "Ceramic" means an inorganic, non-metallic material produced by the application of heat. Ceramics are typically hard, porous, and brittle and, in contrast to glasses or glass-ceramics, exhibit an essentially pure crystalline structure.

[0032] "Crystalline" means a solid composed of atoms arranged in a periodic pattern in three dimensions (i.e., having a long-range crystalline structure as determined by X-ray diffraction). Crystalline structures include tetragonal, monoclinic, cubic zirconia, and mixtures thereof.

[0033] By "homogeneous color and / or translucency gradient" is meant a linear set of colors or translucencies, or a combination of colors and translucencies, rather than a stepped or staggered gradient. The gradient can be axial, radial, or conical in one, two, or three dimensions.

[0034] If desired, the presence of a homogeneous color gradient can be inspected visually or more precisely by using image analysis software (e.g., ImageJ) as described in the Examples section.

[0035] A "mold" is typically a block having a hollow cavity intended to be filled with a material that is then compressed or solidified.

[0036] "Powder" means a dry bulk composed of multiple particles that can flow freely when shaken or tilted.

[0037] "Particle" means a solid substance having a geometrically determinable shape. The shape may be regular or irregular. Particles may typically be analyzed, for example, with respect to particle size and particle size distribution.

[0038] The particle size (d50) of a powder can be obtained from the cumulative particle size distribution curve. Each measurement can be performed using a commercially available particle size analyzer. "D" represents the diameter of the powder particle, and "50" refers to the volume percentage of the particle. In some cases, 50% is expressed as "0.5". For example, "(d50) = 1 μm" means that 50% of the particles have a size of 1 μm or less.

[0039] "Density" refers to the ratio of an object's mass to its volume. Density is typically measured in units of g / cm. 3 The density of an object can be calculated, for example, by determining its volume (e.g., by calculation or by applying Archimedes' principle or method) and measuring its mass.

[0040] The volume of the sample can be determined based on the overall external dimensions of the sample. The density of the sample can be calculated from the measured sample volume and sample mass. The total volume of the material can be calculated from the sample mass and the density of the material used. The total volume of air bubbles in the sample is assumed to be the remainder of the sample volume (100% minus the total volume of the material).

[0041] "Porous material," in the ceramic arts, refers to a material that contains partial volumes formed by voids, pores, or bubbles.

[0042] The terms "sintering" and "firing" are used interchangeably. The porous ceramic article shrinks during the sintering process, i.e., when a suitable temperature is applied. The sintering temperature applied varies depending on the ceramic material selected. For zirconia-based ceramics, a typical sintering temperature range is 1,100°C to 1,600°C. Higher temperatures may be required if sintering is performed at a high heating rate. Sintering typically involves densifying a porous material into a less porous material (or a material with fewer voids) with a higher density, and in some cases may also involve a change in the material phase composition (e.g., partial conversion from an amorphous phase to a crystalline phase).

[0043] A dental zirconia article is classified as "pre-sintered" when it has been treated by heating (temperature range of 900°C to 1,100°C), typically for 1 hour to 3 hours, to such an extent that the biaxial flexural strength of the dental ceramic is in the range of 8 MPa to 80 MPa or 15 MPa to 55 MPa, as measured according to the "three ball punch test", ISO 6872:2015.

[0044] Pre-sintered dental ceramics typically have a porous structure and their density (typically about 3.0 g / cm for yttrium-stabilized zirconia ceramics) 3 ) is a fully sintered dental ceramic framework (typically yttrium-stabilized zirconia ceramic at approximately 6.1 g / cm 3 ) is lower than

[0045] "Coloring ions" shall mean ions that, when dissolved in water (e.g., about 0.6 mol / L), have absorption in the macroscopic spectral range (e.g., 380 nm to 780 nm) and are thereby capable of producing a colored (visible to the naked eye) solution, and in particular, ions that produce a coloring effect in a sintered zirconia article after treatment with a coloring solution. Coloring ions may also be present in the powder (typically as a salt or oxide component) used to make the zirconia article before the powder is compacted.

[0046] "Fluorescent agent or component" shall mean an agent capable of producing fluorescence that is measurable as emission in the visible light range (380 nm to 780 nm).

[0047] "Machining" means milling, grinding, cutting, carving, or shaping a material with a machine. Milling is usually faster and more cost-effective than grinding. A "machinable article" is an article that has a three-dimensional shape and is strong enough to be machined.

[0048] "Ambient conditions" refers to the conditions to which the compositions described herein are typically exposed during storage and handling. Ambient conditions may be, for example, a pressure of 900 mbar to 1,100 mbar, a temperature of 10°C to 40°C, and a relative humidity of 10% to 100%. In a laboratory, ambient conditions are typically adjusted to 20°C to 25°C, 1000 mbar to 1025 mbar, and a relative humidity of 40% to 60%.

[0049] If a composition does not contain a particular component as an essential feature, the composition is "essentially or substantially free" of the component. Therefore, the component is not intentionally added to the composition, either alone or in combination with other components or ingredients of other components. A composition that is essentially free of a particular component usually does not contain that component at all. However, the presence of a small amount of the component may be unavoidable, for example, due to impurities contained in the raw materials used.

[0050] As used herein, "a," "an," "the," "at least one," and "one or more" are used interchangeably. Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0051] "And / or" means either one or both. For example, the phrase component A and / or component B refers to component A only, component B only, or both component A and component B.

[0052] Adding "(s)" to a term means that the term is to include the singular and the plural. For example, the term "additive(s)" means one additive as well as two or more additives (e.g., two, three, four, etc.).

[0053] Unless otherwise indicated, all numbers used in the specification and claims expressing quantities of ingredients, measurements of physical properties, e.g., those set forth below, are to be understood as being modified in all instances by the term "about."

[0054] The terms "comprise" or "containing" and variations thereof do not have a limiting meaning when these terms appear in the specification and claims. The term "comprise" is intended to include the terms "consist essentially of" and "consist of." "Consisting essentially of" means that certain additional components may be present, i.e., components that do not materially affect the essential properties of the article or composition. "Consisting of" means that no additional components should be present. [Brief explanation of the drawings]

[0055] [Figure 1A] 1 illustrates different mixers that can be used in the methods described herein. [Figure 1B]1 illustrates different mixers that can be used in the methods described herein. [Figure 1C] 1 illustrates different mixers that can be used in the methods described herein. [Figure 1D] 1 illustrates different mixers that can be used in the methods described herein. [Figure 1E] 1 illustrates different mixers that can be used in the methods described herein. [Figure 1F] 1 illustrates different mixers that can be used in the methods described herein. [Figure 2A] 1 illustrates different patterns of mixer configurations that can be used in the methods described herein. [Figure 2B] 1 illustrates different patterns of mixer configurations that can be used in the methods described herein. [Figure 2C] 1 illustrates different patterns of mixer configurations that can be used in the methods described herein. [Figure 2D] 1 illustrates different patterns of mixer configurations that can be used in the methods described herein. [Figure 3A] 1 illustrates another configuration of a mixer that can be used in the methods described herein. [Figure 3B] 1 illustrates another configuration of a mixer that can be used in the methods described herein. [Figure 4A] 1 illustrates possible mixing profiles (relationship between the rotational speed of a mixing element and its x / z position within the mold cavity). [Figure 4B] 1 illustrates possible mixing profiles (relationship between the rotational speed of a mixing element and its x / z position within the mold cavity). [Figure 4C] 1 illustrates possible mixing profiles (relationship between the rotational speed of a mixing element and its x / z position within the mold cavity). [Figure 4D] 1 illustrates possible mixing profiles (relationship between the rotational speed of a mixing element and its x / z position within the mold cavity). [Figure 5A]Further blending profiles are illustrated in more detail. [Figure 5B] Further blending profiles are illustrated in more detail. [Figure 6] 10 illustrates a blend profile of a non-inventive embodiment. [Figure 7A] 1 shows an image of a dental milling block not according to the present invention. [Figure 7B] 1 shows an image of a dental milling block not according to the present invention. [Figure 7C] 1 shows an image of a dental milling block of the present invention and an associated plot profile. [Figure 7D] 1 shows an image of a dental milling block of the present invention and an associated plot profile. [Figure 8] 1 shows micrographs (binary format) of different zirconia powders. [Figure 9A] 1 shows an image of the sintered body of Example 1 and the associated plot profile. [Figure 9B] 1 shows an image of the sintered body of Example 1 and the associated plot profile. [Figure 10A] 1 shows the experimental setup of Example 2, an image of the sintered body of Example 2, and the associated plot profile. [Figure 10B] 1 shows the experimental setup of Example 2, an image of the sintered body of Example 2, and the associated plot profile. [Figure 10C] 1 shows the experimental setup of Example 2, an image of the sintered body of Example 2, and the associated plot profile. [Figure 11] 1 shows an SEM image of the sintered body obtained in Example 3. [Figure 12A] 1 shows the experimental setup of Example 4, an image of the sintered body of Comparative Example 1, and the related plot profile. [Figure 12B] 1 shows the experimental setup of Example 4, an image of the sintered body of Comparative Example 1, and the related plot profile. [Figure 12C] 1 shows the experimental setup of Example 4, an image of the sintered body of Comparative Example 1, and the related plot profile. [Figure 12D] 1 shows the experimental setup of Example 4, an image of the sintered body of Comparative Example 1, and the related plot profile. [Figure 13A] 1 shows an experimental setup and an image of a sintered body of Comparative Example 1. [Figure 13B] 1 shows an experimental setup and an image of a sintered body of Comparative Example 1. [Figure 13C] 1 shows an experimental setup and an image of a sintered body of Comparative Example 1. [Figure 13D] 1 shows an experimental setup and an image of a sintered body of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0056] The compositions described herein have been found to have several advantageous properties.

[0057] The use of mixing elements to mix powder compositions is generally known. However, it has surprisingly been found that it is also possible to mix powders located only in specific regions or locations of a larger volume in a controlled manner, thereby creating gradients within the powder composition.

[0058] In particular, this can be achieved if the mixing elements used to mix the powder compositions not only rotate during the mixing process, but also already rotate in the step in which the mixing elements are introduced into the powder compositions to be mixed, and continue to rotate when the mixing elements are removed from the mixed powder compositions.

[0059] While rotating, the mixing element carries the powder already mixed from the upper region of the powder composition to the intermediate or interface region where the two powders to be mixed come into contact with each other. Similarly, while rotating the mixing element, it carries the already mixed powder to the upper region of the powder composition, which contributes to a smooth gradient.

[0060] If the mixing elements are not rotating when introduced into the powder composition, the powder composition may already be slightly compacted, which can be counterproductive during the subsequent mixing process.

[0061] It has been observed that if the mixing element is not rotating when removed from the mixed powder composition, the mixed powder composition is often scattered or transferred to other areas of the powder composition that are not intended to be mixed.

[0062] Thus, by using a mixing element that not only rotates when introduced into the area of ​​the powder composition to be mixed, but also rotates when the mixing element is removed from the mixed powder composition, a homogeneous powder gradient can be obtained in a defined area of ​​the powder composition to be mixed.

[0063] It was surprising that this effect could be achieved with such small amounts of powder composition.

[0064] The invention described herein relates to a method for manufacturing a dental milling block, which method comprises several steps.

[0065] In a first step, a first volume V of a first powder (e.g., powder A) is added. P1 is filled into the cavity of the mold.

[0066] The mold has a cavity with a vertical z-direction and horizontal x / y-directions perpendicular to the z-direction. In the z-direction, there is an opening into the mold cavity for receiving the powder to be mixed. The shape and size of the mold cavity typically essentially correspond to the shape of the dental milling block to be produced. In many cases, the mold cavity has a cylindrical, cubic, or rectangular shape. If desired, other shapes, including horseshoe, elliptical, spherical, etc., can also be used. When producing dental milling blocks, the volume of the mold cavity typically ranges from 2 mL to 2,000 mL, or from 5 mL to 500 mL, or from 10 mL to 300 mL.

[0067] The powder composition can be filled into the mold cavity by a variety of means, including a vibratory feeder, a screw feeder, or by using a filling shoe, which may be preferred as it facilitates layer-by-layer filling of the mold.

[0068] In a further step, a second volume V of a second powder (e.g., powder B) is added. P2 is packed into the cavity on top of the first powder.

[0069] The first powder is filled into the mold cavity to a height H1, which represents the top level of the first powder. The height H1 is typically within the range of 1 mm to 99 mm, 1 mm to 90 mm, 2 mm to 80 mm, or 2 mm to 70 mm.

[0070] The second powder is filled into the mold cavity to a height H2, which represents the upper level of the powder composition filled into the mold cavity. Height H2 is typically in the range of 25 mm to 100 mm, 30 mm to 90 mm, or 40 mm to 80 mm.

[0071] Depending on the means or elements used to pack the powder into the cavity of the mold, the height in the x and y directions, especially of the first powder, may not be uniform. The height can be a function of x and y: H 1(x,y),2(x,y) The top surface of the powder composition filled into the cavity of the mold is typically flat.

[0072] According to one embodiment, the first powder and the second powder typically form parallel layers. If the height z of the dental milling block to be produced is smaller than the dimensions in the x / y direction, for example if the dental milling block has a disk-like shape, it may be preferable to pack the powders layer by layer.

[0073] According to another embodiment, a first powder forms a cone in the mold having a height H1, a second powder is applied on top of the first powder to fill the remaining space between the cone surface and the mold boundary up to height H1, and an additional layer of the second powder is applied on top to height H2.

[0074] Filling the mold with the first powder in a cone shape may be desirable because it can help better replicate or mimic the appearance of a natural tooth, which has an inner dentin portion and an outer enamel portion that is more translucent than the dentin portion. When the first powder forms a cone intended to mimic the dentin portion of a dental restoration that will later be fabricated, the color and / or translucency of the first powder after sintering is typically darker and / or less translucent than the second powder.

[0075] If desired, more complex surface shapes can be produced, for example by using vibration or screw feeders.

[0076] According to one embodiment, only two different powders A and B are used, although it may be desirable to fill the mold with additional powders, for example, a third volume of powder C and / or a fourth volume of powder D.

[0077] Powder V P1 and V P2 The individual volumes of may be the same or different. If they are different, the volumes typically differ from each other by no more than 5% to 60%, or 10% to 50%, or 15% to 40%.

[0078] The volume of powder used typically depends on the size and volume of the dental milling block being produced.

[0079] The volume refers to the bulk volume of the powder as it is packed into the mold cavity in powder form. The bulk volume of an individual powder is typically 0.9 g / cm 3 ~2g / cm 3 or 1g / cm 3 ~1.8g / cm3 The range is.

[0080] The first powder and the second powder differ from each other in terms of their physical properties and / or chemical composition and / or color, and differences in chemical composition and / or color may be preferred.

[0081] The chemical composition of the powder is described further herein below. The chemical composition can also affect the translucency of the sintered product.

[0082] According to a preferred embodiment, the powders differ from one another in terms of color, which can be achieved, for example, by using different amounts of coloring components, or by using different coloring components, or by using a mixture of both.

[0083] According to another embodiment, the powders comprise a ceramic component and a stabilizing component and differ from each other with respect to the content of the stabilizing component.

[0084] The method for producing a dental milling block also includes providing a mixer unit. The mixer unit typically includes a motor for driving a mixer shaft that includes or has a mixing element attached thereto. Depending on the shape of the mixer shaft, the mixing element can form part of the mixer shaft.

[0085] The mixing elements should have a form or shape that allows controlled, localized transport or movement of the powders to be mixed, at least in the z-direction of the mold. The mixing elements can have different shapes, for example, helical or spiral, single-bladed, multi-bladed, screw-shaped, auger-shaped, or a combination thereof. If the mixing elements have a bladed shape, the blades are typically angular.

[0086] The mixer shaft includes at least one mixing element. If the mixer shaft includes two or more mixing elements (e.g., 2 to 8 or 3 to 6), the mixing elements are typically arranged symmetrically with respect to one another. However, it is also possible for the mixing elements to be arranged at different heights on the mixer shaft or not symmetrically.

[0087] Compared to mixers described in the prior art, the mixer shafts described herein are significantly shorter: Typical lengths of the mixer shafts range from 0.5 cm to 15 cm, or 1 cm to 10 cm, or 2 cm to 8 cm, or 3 cm to 6 cm.

[0088] Possible shapes of mixing elements are shown in Figures 1A-1F. Figure 1A shows a mixer with a rotor-shaped mixing element with four blades. Figure 1B shows a mixer with a rotor-shaped mixing element with two blades. Figure 1C shows a mixer with a hollow spiral-shaped mixing element. Figure 1D shows a mixer with cross spiral-shaped elements. Figure 1E shows a mixer with a screw conveyor-shaped or auger-shaped mixing element. Figure 1F shows a mixer with two angled blades spaced apart from the mixer shaft.

[0089] The mixer unit may include two or more mixer shafts. The number of mixer shafts and the corresponding number of mixing elements is not particularly limited, but is typically related to the size and dimensions of the mold cavity that contains the powders to be mixed. When the size or volume of the powders to be mixed is larger, it may be beneficial for the mixer unit to include 2 to 30 or 3 to 20 mixer shafts.

[0090] The mixer shafts may be arranged in different patterns. Circular, triangular, square, rectangular, or polygonal (e.g., 5, 6, 7, or 8) pattern arrangements may be beneficial. It may be preferable if a pattern is used that essentially covers the complete area of ​​the powders to be mixed. In this regard, the use of mixing elements of different sizes may be useful. Such an arrangement may be advantageous, since horizontal movement of the mixing elements may no longer be required, allowing the mixing process to be carried out in a shorter time.

[0091] Possible patterns in which mixer shafts can be arranged are shown in Figures 2A-2D. Figure 2A shows a mold (dark gray area) with a circular cavity (light gray area) in the x / y direction. Disposed within the cavity is a mixer with a dual-blade mixing element that is movable in both the x / y and z directions. In Figure 2B, the mixing element is larger and not movable in the x / y direction. In Figure 2C, a rectangular cavity with rounded edges is shown within the mold. Disposed within the cavity are four mixers with dual-blade mixing elements. The mixing elements are essentially movable only in the z direction. In Figure 2D, a circular cavity is shown within the mold. Disposed within the cavity are 22 mixers with dual-blade mixing elements. The mixing elements are essentially movable only in the z direction.

[0092] The mixer should be movable in at least the z-direction relative to the powder and mold. It may be advantageous for the mixer to be movable in the x or y direction as well. It may also be advantageous for the mixer to be movable in the z, x, and y directions independently.

[0093] If there are only a few mixer shafts (e.g. 2-4) or even just one, it may be beneficial for one or more mixer shafts to be individually movable horizontally (in the x / y direction of the mold cavity). If there are more mixer shafts, it may be advantageous for the mixer shafts to be individually rotatable. The individual rotation of the mixer shafts may be clockwise or counterclockwise. It is also possible for the mixer shafts to be like rotating planetary gears. The length and / or position of the mixing elements on the mixer shaft may vary.

[0094] Figures 3A and 3B show mixer arrangements that can be used in the methods described herein. Figure 3A shows the mold in the z-direction. A cone of first powder (dark gray) is placed in the mold cavity (the volume of which is adjusted by the lower punch) to a height H1. A second powder is placed above the first powder to a height H2. Three individual rotating mixers are placed within the second powder, one rotating clockwise and the other two rotating counterclockwise. Figure 3B shows the same configuration, but with a different mixer arrangement. Five mixers (rotating in the same direction) are shown, which are placed at different levels of the second powder near the middle or interface region.

[0095] The powder mixed in the intermediate region typically covers up to 90%, or up to 80%, or up to 70%, or up to 60%, or up to 50% of the overall height of the powder composition filled into the mold.

[0096] When the mixing elements are introduced into the intermediate region of the powders to be mixed, they are typically not moved in the z direction over a distance that exceeds 50% of the height H1 of the first powder.

[0097] The rotation speed used is typically also related to the shape and size of the mixing elements. For larger sized mixing elements, slower rotation speeds are typically used. For mixing the powders described herein, rotation speeds in the range of 10 rpm to 10,000 rpm, or 20 rpm to 1,000 rpm, or 30 rpm to 800 rpm for the individual mixer shafts have been found to be useful.

[0098] Too high a rotation speed can adversely affect the desired color and / or composition gradient in the powder composition.Using a fairly low rotation speed can be beneficial to limit the mixing process to a specific region of the powder composition being mixed.This can be advantageous if the rotation speed and / or direction of each mixer shaft is adjusted during the entire production process.The vertical movement of the mixing elements can be combined with horizontal movement.

[0099] When the mixing element is introduced into the powder, the rotation speed is typically slower than the rotation speed used to mix the intermediate region of the first and second powders. When the mixing element is removed from the powder composition, the rotation speed is also typically slower than the rotation speed used to mix the intermediate region of the first and second powders.

[0100] According to one embodiment, the rotating mixing elements are moved into the powder composition, partially out of the powder composition, partially into the powder composition again, and removed from the powder composition, allowing for variations in rotation speed, movement speed, and placement and positioning of the individual mixers to be varied as desired.

[0101] The speed, direction, and position of the individual mixer shafts and mixing elements are typically electronically controlled (e.g., mechanically controlled). A control unit can effect the rotational speed, time, and position of the individual mixer shafts and / or mixing elements.

[0102] Generally, the mixing process is adjusted to obtain a dental milling block having a homogeneous gradient in chemical composition and / or color at least in the z-direction in an intermediate region of the first powder and the second powder.

[0103] However, it is also possible to produce dental milling blocks with a homogeneous gradient in terms of chemical composition and / or color in the z-direction and in the x / y-direction.

[0104] The gradient typically spans at least 20%, or at least 30%, or at least 40%, or at least 50% of the combined height of the first and second powders in the z-direction of the dental milling block.

[0105] Examples of mixing profiles that can be used are shown schematically in Figures 4A-4D, where the rotational speed is given on the y-axis and the position of the mixing element within the powder composition is given on the x-axis.

[0106] Figures 4A-4D illustrate possible relationships between the rotational speed (ω) of a mixing element and its z and x positions within the mold cavity for embodiments of the present invention. The rotational speed of the mixer can be constant (Figures 4A-4C) or stepped (Figure 4D). The movement of the mixer in the x direction can be stepped (Figures 4A-4D). The movement of the mixer in the z direction can be linear (in and out), as shown in Figure 5A, or follow a variety of different schemes, as shown in Figures 4A-4D.

[0107] Figure 5A shows the configuration for the mold in the z-direction. Within the cavity of the mold, there is a cone of a first powder (dark grey) filled to a height H1 of 15 mm. Above the first powder, there is a second powder (light grey) filled to a height H2 of 35 mm. A rotating mixer is introduced into the powder composition in the z-direction at a speed of 1 mm / s while rotating at 600 rpm. After a certain time, the rotating mixer is removed from the powder composition at a speed of 1 mm / s.

[0108] A different configuration is shown in Figure 5B. The first and second powders are filled into the mold cavity in layers, and differently shaped mixing elements are used. The rotation speed of the mixing elements is fairly slow when entering the powder composition and increases to a plateau when reaching the intermediate region of the powder composition. Increasing the rotation speed in the intermediate region during the process can contribute to reducing the overall mixing time. In other words, at least one mixing element has a rotation speed RS2 at height H2 when introduced into the powder, and a rotation speed RS1 at height H1, where RS1 is different from RS2, specifically RS1 > RS2.

[0109] A non-inventive embodiment is shown in Figure 6. The mixing elements rotate only during the mixing process, and do not rotate when being introduced into or removed from the powder composition.

[0110] Photographs of a non-inventive dental milling block after sintering are shown in Figures 7A and 7B. In Figure 7A, the powder placed in the mold cavity was not mixed at all. In Figure 7B, the powder placed in the mold cavity was mixed, but the mixer did not rotate during introduction into and removal from the powder composition, but only during mixing in the intermediate region of the powder composition.

[0111] A photograph of the dental milling block of the present invention after sintering is shown in Figure 7C. The powder placed in the cavity of the mold was mixed. The mixer rotated during introduction into the powder composition, during mixing of the powder composition in the intermediate region, and during removal from the powder composition. Figure 7D shows a profile obtained by using the plot profile function of ImageJ software for the region of interest. A smooth color transition is evident.

[0112] In a further step, the powder placed in the cavity of the mold is compressed, typically into a so-called green body.

[0113] If desired, pressing aids can be added to facilitate the compaction process. Suitable pressing aids include binders, lubricants, and mixtures thereof. The addition of pressing aids to the powder is typically done before the powder is filled into a mold.

[0114] The pressure applied is typically in the range of 5 MPa to 400 MPa or 100 MPa to 250 MPa.

[0115] Alternatively, the pressure applied may be such that the pressed body has a particular density, e.g., 2.8 g / cm for a compacted article of zirconia powder. 3 ~3.5g / cm 3 is set to reach a density of

[0116] In a further step, the compacted powder can be subjected to a heat treatment or pre-sintering step, if desired, in order to obtain a porous dental mill blank.

[0117] The temperature of the heat treatment is typically in the range of 800° C. to 1,100° C., or 900° C. to 1,000° C. The heat treatment is typically applied for a duration of 10 hours to 150 hours, or 35 hours to 100 hours.

[0118] After pressing or pre-sintering the powder, the resulting article can be machined or sliced ​​into any desired shape.

[0119] The powders used to manufacture dental milling blocks can be characterized by their physical-mechanical properties.

[0120] The powders used in the methods described herein should be free-flowing. Free-flowing means that the particles of the powder flow without adhering to each other or clumping. The flowability of a powder can also be described by its angle of repose. The lower the value, the less cohesive the individual powder particles have. It has been found to be advantageous to use powders with angles of repose in the range of 15° to 35°, as this facilitates laminar mixing.

[0121] In addition, the powder has the following characteristics: a) the powder particles of the powder have a predominantly spherical shape; b) 4m 2 / g~20m 2 / g, c) the powder particles are agglomerates or aggregates of smaller particles; d) having a powder particle size d50 in the range of 25 μm to 150 μm; e) 0.9 g / cm 3 ~2g / cm 3 having a bulk density of may be characterized by the following alone or in combination:

[0122] Combinations of features (a) and (b), or (a) and (d), or (b) and (c), or (a), (b), and (c) may be advantageous.

[0123] The predominant shape of the particles (greater than 50%) is typically spherical. Spherically shaped particles typically flow better than milled particles. Spherically shaped particles can be produced by spray drying.

[0124] The use of powders with BET surfaces in the above ranges can be beneficial as it typically allows for more homogeneous sintering of the subsequent composition.

[0125] The particle size d50 of the powder should not be too high, otherwise it may be more difficult to obtain a smooth color and / or composition gradient. Using powders with similar or identical particle sizes (d50) can also be useful to facilitate the creation of smooth color and / or composition gradients during the mixing process.

[0126] More specifically, the powders to be mixed must differ from each other by no more than a given percentage with respect to the following properties: BET surface: no more than 20%; particle size d50: no more than 20%; angle of repose: no more than 20%.

[0127] Various types of powders can be used to manufacture dental milling blocks, including ceramic powders. Examples of ceramic powders include zirconia powder and alumina powder, among others. The use of ceramic powders to manufacture dental milling blocks can be preferred due to their high strength.

[0128] According to one embodiment, the dental milling block produced is a dental zirconia milling block.

[0129] The powder composition used to make dental zirconia milling blocks includes a ceramic component and a stabilizing component. Optionally, coloring and fluorescent components may be present.

[0130] The ceramic component is typically selected from oxides of Zr, Hf, Al and mixtures thereof.

[0131] Thus, in addition to zirconia, zirconia dental milling block materials typically contain oxides of Hf and optionally Al, typically in very small amounts (e.g., less than 3 wt. % for hafnia and less than 0.15 wt. % for alumina).

[0132] The stabilizing component is typically selected from oxides of Y, Mg, Ca, Ce, and mixtures thereof (eg, Y2O3, MgO, CaO, CeO2), with the oxide of Y being preferred.

[0133] If present, the coloring components are typically selected from oxides of Fe, Mn, Cr, Ni, Co, Er, Pr, Tb, Nd, in particular oxides of Mn, Er, Pr, Tb, Co and mixtures thereof (e.g. MnO2, Er2O3, Tb4O7, CoO).

[0134] When present, the fluorescent agent is typically selected from oxides or hydroxides of Bi, and mixtures thereof.

[0135] The ceramic component is typically present in an amount of 80% to 95% by weight, or 85% to 95% by weight, or 90% to 95% by weight, based on the weight of the dental milling block.

[0136] The stabilizing component is typically present in an amount of 3% to 12%, or 5% to 10%, or 6% to 10% by weight based on the weight of the dental milling block.

[0137] When present, the coloring component is typically present in an amount of 0.01% to 2%, or 0.02% to 1.5%, or 0.03% to 1.2% by weight based on the weight of the dental milling block.

[0138] When present, the fluorescent agent is typically present in an amount of 0% to 1%, or 0.005% to 0.8%, or 0.01% to 0.1% by weight, based on the weight of the dental milling block.

[0139] The weight percentages are calculated based on the amount of each oxide or ceramic component, stabilizing component, coloring component, and fluorescent agent.

[0140] To obtain an aesthetic dental article, the following concentrations have been found to be useful: Ceramic component: 80% by weight to 95% by weight, or 85% by weight to 95% by weight, Stabilizing component: 3% by weight to 12% by weight, or 5% by weight to 11% by weight, Coloring component: 0% by weight to 2% by weight, or 0.01% by weight to 1.5% by weight, Fluorescent agent: 0% by weight to 1% by weight, or 0.005% by weight to 0.8% by weight, The weight percentages are based on the weight of the porous dental milling block.

[0141] According to one embodiment, the powder used to manufacture the dental milling blocks comprises: ZrO2 content: 70 mol% to 98 mol%, or 80 mol% to 97 mol%, HfO2 content: 0 mol% to 2 mol%, or 0.1 mol% to 1.8 mol%, Y2O3 content: 1 mol% to 15 mol%, or 1.5 mol% to 10 mol%, or 2 mol% to 5 mol%, Al2O3 content: 0 mol% to 1 mol%, or 0.005 mol% to 0.5 mol%, or 0.01 mol% to 0.1 mol% can be characterized as:

[0142] According to a further embodiment, the powder used to manufacture dental milling blocks comprises: ZrO2 content: 90 mol% to 98 mol%, HfO2 content: 0 mol% to 2 mol%, Y2O3 content: 3 mol% to 5 mol%. Al2O3 content: 0 mol% to 0.1 mol% It can be characterized as:

[0143] A higher Y2O3 content typically results in an increase in the cubic phase in the zirconia ceramic material after the material is sintered to final density. A higher cubic phase content may contribute to better or higher translucency.

[0144] According to one embodiment, the porous dental zirconia article material contains about 3, 4, or 5 mole percent yttria. These materials have been found to be particularly useful in producing aesthetic zirconia dental restorations in the firing process described herein.

[0145] In another embodiment, the powder used to manufacture the dental milling block comprises: ZrO2+HfO2: 90% to 95% by weight, Y2O3: 4% to 10% by weight, Al2O3: 0wt%~0.15wt%, Colored oxide: 0.01% to 2% by weight, and the weight percentages are based on the weight of each powder.

[0146] Although the presence of alumina is not required, the presence of small amounts of alumina can be beneficial because it can contribute to better hydrothermal stability of the sintered zirconia article. However, too much alumina can adversely affect the translucency of the sintered zirconia article. Therefore, alumina may be present in an amount of 0 wt. % to 0.15 wt. %, or 0.001 wt. % to 0.12 wt. %, or 0.01 wt. % to 0.1 wt. %.

[0147] For producing the dental milling blocks described herein, at least two powders are used that differ from each other in terms of chemical composition and / or color, and each powder may differ from each other in terms of yttria content and / or the amount or nature of the coloring component.

[0148] According to one embodiment, Powder A has a lower yttria content than Powder B. After sintering, each composition has a different translucency: areas with higher yttria content are typically more translucent than areas with lower yttria content.

[0149] According to another embodiment, powder A has a higher content of coloring components than powder B.

[0150] Suitable powders may have the following formulation and properties:

[0151] First Powder Ceramic content: over 80% by weight Stabilizing component: yttria in an amount of 1 mol% to 5 mol% or 2 mol% to 3 mol%, Coloring components: 0% to 2% by weight (based on each oxide of the coloring components), 4m 2 / g~20m 2 / g, having a particle size d50 in the range of 25 μm to 150 μm; Have an angle of repose of 15° to 35°.

[0152] Second powder Ceramic content: over 80% by weight Stabilizing component: yttria in an amount of 1 mol% to 5 mol% or 4 mol% to 5 mol%, Coloring components: 0% to 2% by weight (based on each oxide of the coloring components), 4m 2 / g~20m 2 / g, having a particle size d50 in the range of 25 μm to 150 μm; Have an angle of repose of 15° to 35°.

[0153] However, for purposes of producing the dental milling blocks described herein, the first and second powders differ from one another at least with respect to the amount of stabilizing and / or coloring components present in each powder.

[0154] After powder compaction and an optional pre-sintering step, the pre-sintered dental milling block material typically has the following characteristics: BET surface: 5m 2 ~20m 2 , Density: 2.5g / cm 3 ~4g / cm 3 and average particle size: 50 nm to 200 nm, either alone or in combination. Combinations of features a) and b), a) and c), and a), b), and c) may be preferred.

[0155] It may be advantageous in some cases to use dental zirconia milling blocks whose material has a BET surface in the range specified above, as this ensures proper sintering activity of the material before and during the subsequent sintering process.

[0156] Without being bound by any particular theory, it is believed that if the BET surface is too high, there will be too many pores in the sintered porous dental zirconia article. This may adversely affect the sintering of the article, making it more difficult to obtain a dental zirconia article with adequate strength and / or translucency. On the other hand, if the BET surface is too low, the porous zirconia article may not have adequate sintering activity. This may adversely affect the sintering behavior of the porous dental zirconia article during the first heat treatment step (e.g., sintering shrinkage, degassing of residual sintering aids). When referring to the BET surface, in this context, it refers to the surface of the sintered dental milling block, not the surface of the powder composition used to produce the block.

[0157] Alternatively or additionally, the material of the pre-sintered dental milling block may have the following parameters: a) Biaxial bending strength: Measured according to ISO6872:2015, which is suitable for measurements in a porous state (measurement setup: 3.6 mm punch diameter, loading rate 0.1 mm / min, sample thickness 2 mm, support ball diameter 6 mm, support ball diameter 14 mm) 15 MPa to 55 MPa; b) Vickers hardness: 15 to 150 (HV 0.5) or 20 to 140 (HV 0.5), may be characterized by the following alone or in combination:

[0158] If desired, each characteristic can be measured as described in the Examples section.

[0159] If the Vickers hardness of the material is too low, the machinability may be adversely affected (chipping or breaking of the edges of the workpiece) and the ease of manual reworking to individualize the dental restoration or the frame of the monolithic restoration may be impaired. If the Vickers hardness of the material is too high, the wear on the machining tools may increase, shortening the tool life to unacceptable levels, or the tools may break and destroy the workpiece.

[0160] It has been found that if the biaxial flexural strength of a material is too low, the material may be prone to cracking during milling or manual finishing by a dental technician. On the other hand, if the biaxial flexural strength of a material is too high, milling the material with a milling machine is often impossible with proper practice. The milling tools used or the milled material may be prone to chipping or breakage. In such cases, shaping of the material has had to be achieved by grinding, for example, using a Cerec™ grinding machine (Sirona).

[0161] Dental milling blocks are typically provided to customers in a configuration that allows for mounting of the dental milling block in a milling machine.

[0162] Either the top or bottom surface of a zirconia dental mill blank typically includes marking elements (e.g., printing or carving) that facilitate proper orientation of the dental milling block within the milling machine.

[0163] Attachment or fastening of the dental zirconia mill blank to machining equipment, particularly the clamping fixtures of such equipment, can also be accomplished by providing the blank with suitable means therefor, including frames, notches, stubs, mandrels, and combinations thereof.

[0164] In another embodiment, the dental milling block is fixed to or housed in a holding device. The holding device housing the dental milling block can then serve as a means for attaching the blank to a machining device. The dental milling block can be fixed to the holding device by clamping, gluing, screwing, and combinations thereof. Useful holding devices include frames (openable), stubs, or mandrels. The use of a holding device can facilitate the production of dental articles by a machining device. Examples of useful holding devices are described in U.S. Pat. No. 8,141,217 (B2) (Gubler et al.), WO 02 / 45614 (A1) (ETH Zurich), DE 20316004 (U1) (Stuehrenberg), U.S. Pat. No. 7,985,119 (B2) (Basler et al.), or WO 01 / 13862 (3M). The contents of these documents regarding the description of retention devices are incorporated herein by reference.

[0165] Dental milling blocks typically have a blank or rectangular or disc shape.

[0166] When the dental milling block has a rectangular shape, the zirconia dental milling block typically has the following dimensions: x dimension: 12 mm to 45 mm or 15 mm to 40 mm, y dimension: 12 mm to 70 mm or 15 mm to 60 mm, z dimension: 10 mm to 40 mm or 15 mm to 25 mm.

[0167] When the dental milling block has a disc shape, the dental zirconia mill blank typically has the following dimensions: x, y dimensions: 90 mm to 110 mm or 95 mm to 105 mm, z dimension: 5 mm to 35 mm or 10 mm to 30 mm.

[0168] Further, possibly preferred embodiments are described below.

[0169] Embodiment 1 10. The method for producing a dental milling block as described herein, wherein the first and second powders are characterized by an angle of repose of 15° to 35° and a powder particle size d50 of 25 μm to 150 μm.

[0170] Embodiment 2 A method for producing dental milling blocks as described herein, wherein the first and second powders are characterized by an angle of repose between 15° and 35° and a powder particle size d50 between 25 μm and 150 μm, and the mixed powders differ from each other by no more than a given % with respect to the following properties: particle size d50: no more than 20%; angle of repose: no more than 20%.

[0171] Embodiment 3 A method for manufacturing a dental milling block as described herein, wherein the mixing elements are moved in the z-direction over a distance of less than 80% of the height H2, and at least one mixing element has a spiral or auger shape.

[0172] Embodiment 4 A method for manufacturing a dental milling block as described herein, wherein at least one mixing element is moved or movable in the x / y direction, and the powder mixed in the intermediate region extends to less than 90% of the cavity dimension in the x / y direction of the cavity.

[0173] Embodiment 5 10. The method of making a dental milling block as described herein, wherein the first powder is applied in the form of a cone, and the first and second powders have an angle of repose of 15° to 35°.

[0174] Embodiment 6 A method for manufacturing a dental milling block as described herein, wherein the first and second powders are characterized by an angle of repose of 15° to 35° and a powder particle size d50 of 25 μm to 150 μm, and at least one mixing element is moved or movable in the x / y direction, and the powders mixed in the intermediate region extend to less than 90% of the cavity dimension in the x / y direction of the cavity.

[0175] Embodiment 7 The method for producing a dental milling block as described herein, wherein the first and second powders are characterized by an angle of repose of 15° to 35°, and at least one mixing element has a rotation speed RS2 at a height H2 and a rotation speed RS1 at a height H1, wherein RS1 is different from RS2.

[0176] Embodiment 8 A method for producing a dental milling block as described herein, wherein the first and second powders are characterized by an angle of repose of 15° to 35°, and at least one mixing element has a rotation speed RS2 at a height H2 and a rotation speed RS1 at a height H1, where RS1>RS2.

[0177] In contrast to the methods described in the prior art, according to the present invention only certain portions of the powder compositions are mixed, not the entire amounts.

[0178] Furthermore, the methods described herein typically do not include the following steps, alone or in combination: a) providing a pattern on the surface of the first and / or second powder; b) applying a third powder over the second powder, where the third powder differs in chemical composition from the first and second powders.

[0179] The present invention also relates to a method of making a dental restoration.

[0180] This method is producing a dental milling block according to the method described herein; applying heat to the compressed powder to obtain a heat-treated dental milling block; machining a dental restoration from the heat-treated dental milling block; and sintering the dental restoration.

[0181] Machining can be performed using commercially available milling equipment, such as the Cercon™ from DentsplySirona. Optionally, sintering can be performed by applying one of the following heat treatment processes: a) sintering temperature of 1,350°C to 1,600°C, heating rate of 1°C / s to 7°C / s; b) sintering temperature of 1,350°C to 1,600°C, heating rate of 1°C / min to 30°C / min.

[0182] Dental restorations may have a variety of shapes, including those of a dental crown, bridge, veneer, inlay, or onlay.

[0183] The present invention also relates to a kit-of-parts comprising a mold as described herein, a mixer unit as described herein, and a first powder and a second powder as described herein.

[0184] All components used in the dental compositions of the present invention are sufficiently biocompatible, that is, the compositions do not induce a toxic, adverse, or immunological reaction in living tissue.

[0185] The entire disclosures of the patents, patent documents, and publications cited herein are incorporated by reference in their entireties, as if each were individually incorporated. Various modifications and variations to the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The above specification, examples, and data provide a description of the manufacture and use of the compositions and methods of the invention. The invention is not limited to the embodiments disclosed herein. Those skilled in the art will recognize that many alternative embodiments of the invention can be made without departing from the spirit and scope of the invention.

[0186] The following examples are provided to illustrate, but not to limit, the scope of the present invention. [Example]

[0187] Unless otherwise indicated, all parts and percentages are by weight, all water is deionized water, and all molecular weights are weight average molecular weight. Furthermore, unless otherwise indicated, all experiments were conducted at ambient conditions (23°C, 1013 mbar at sea level).

[0188] method elemental composition If desired, elemental composition can be measured by X-ray fluorescence spectroscopy (XRF), for example, using a Rigaku ZSX Primus II. This method is particularly suitable for the analysis of solid, e.g., zirconia ceramic or glass materials.

[0189] fluorescence If desired, the sample is placed in a UV light box, such as those used to examine thin layer chromatography plates. Fluorescence can be detected visually by illuminating the sample against a black background.

[0190] BET surface If desired, the BET surface of a porous article can be measured as follows: total pore volume and average pore diameter can be analyzed using N2 adsorption isotherms and BET surface area analysis. Approximately 0.1 g to 2 g of sample can be cut from a larger sample for insertion into a sample tube (if necessary). All samples are vacuum degassed at 120°C for more than 1 hour before analysis. Samples were then analyzed by N2 gas adsorption and desorption using a Belsorb II (distributed by Robotherm Prazisionsmesstechnik, Bochum, Germany) in a 9 mm cell with a 2 cm bulb and a 5 mm glass rod. At liquid nitrogen temperature, adsorption data points are collected from 0.1 p / p0 to 0.99 p / p0, and desorption points are collected from 0.99 p / p0 to 0.5 p / p0. The specific surface area S is calculated by the BET method with p / p0 of 0.25 to 0.3 (for details on the calculation, see Belsorb Analysis Software User Manual Operating Manual, Chapter 12, Bel Japan, Inc.).

[0191] density If desired, the density of the sintered material can be measured by the Archimedes method. This measurement is performed on a precision balance (designated "BP221S" by Sartorius AG, Gottingen, Germany) using a density measurement kit (designated "YDK01" by Sartorius AG). In this procedure, the sample is first weighed in air (A) and then immersed in solution (B). The solution is a 0.05 wt. % solution of tenside in deionized water (e.g., "Berol 266", Fa. Hoesch). The density is calculated using the formula ρ = (A / (AB))ρ, where ρ is the density of water.

[0192] If the material has a regular shape (e.g., a rectangular parallelepiped), the density can be simply determined by measuring the sample dimensions x, y, and z (e.g., using a sliding caliper (designated "IP67" by Mitutoyo, Japan)) and the weight m of the sample (e.g., using a precision balance (designated "BP221S" by Sartorius AG, Gottingen, Germany). Density can be calculated using the formula ρ=m / (x * y * z).

[0193] Powder bulk density The bulk density can be obtained from the material data sheet provided by the powder supplier or can be determined according to DIN EN ISO 23145-2, where the untapped density of granulated or non-granulated powders is determined by constant volume measurement.

[0194] porosity If desired, porosity can be determined as follows: Porosity = (1 - (density of porous material / density of sintered material)) x 100. As above (under "Density"), the density of a porous material can be calculated by dividing the weight by the volume. The volume can be obtained by geometric measurement.

[0195] Pore ​​volume: Pore ​​volume V of porous zirconia body P is the volume of the zirconia material in the porous body (V Z It can be determined by subtracting (e.g., V = weight of porous body / density of zirconia material) B =x * y * z):V P =V B -V Z As used herein, the density of the sintered zirconia material is 6.08 g / cm 3 This value is believed to be sufficiently accurate to determine the pore volume of a porous zirconia body.

[0196] Particle size (suitable for micro-sized particles) If necessary, particle size distribution, including particle size by volume (d50), can be determined by laser diffraction using a Mastersizer 2000 (Malvern) particle size detector, applying the Fraunhofer approximation. During the measurement, the sample is typically dispersed precisely using ultrasound. For water-insoluble particles, water is typically used as a dispersant.

[0197] Average particle size (pre-sintered or sintered) If desired, the average grain size can be measured using line intercept analysis. FESEM micrographs with 70,000x magnification are used for grain size measurement. For each sample, three or four micrographs taken from different areas of the sintered body are used. Ten horizontal lines spaced approximately equally apart are drawn across the height of each micrograph. The number of grain boundary intercepts observed on each line is counted and used to calculate the average distance between the intercepts. The average distance for each line is multiplied by 1.56 to determine the grain size, and this value is averaged across all lines in all micrographs for each sample.

[0198] Biaxial bending strength If desired, the biaxial flexural strength of pre-sintered materials can be measured according to ISO 6872:2015 with the following modifications: Pre-sintered samples are cut into wafers 2 ± 0.1 mm thick using a dry cutting saw. The diameter of the samples should be 17 ± 2 mm. The parallel large faces of the wafers are ground using silicon carbide abrasive paper (P2500). Each wafer is centered on the support of three steel balls (6 mm diameter balls) with a support diameter of 14 mm. The punch diameter that contacts the wafer is 3.6 mm. The punch is pressed into the wafer at a rate of 0.1 mm / min. A minimum of 15 samples is measured to determine the average strength. Testing can be performed using an Instron 5566 universal testing machine (Instron Deutschland GmbH).

[0199] Vickers hardness If desired, Vickers hardness can be measured according to ISO 14705 with the following modifications: The surface of the pre-sintered sample is ground using silicon carbide abrasive paper (P2500). The surface of the sintered sample is polished with a 20 μm diamond suspension. The test load is adjusted to the hardness level of the sample. The test load used can be between 0.2 kg and 2 kg and can be applied to each recess for 15 seconds. A minimum of 10 recesses is measured and the average Vickers hardness is determined. The test can be performed using a hardness tester Leco M-400-G (Leco Instrumente GmbH).

[0200] Scanning electron microscope (SEM) images If desired, images of the powders and powder compositions in various states (eg, before and after sintering) can be generated by SEM.

[0201] Color Gradient If desired, the image of the color gradient of the colored powder mixture can be further analyzed using the plot profile function in ImageJ software (a Java-based image processing program developed at the National Institutes of Health and the Laboratory for Optical and Computational Instrumentation; not subject to copyright protection). The color gradient is typically considered homogeneous if the image plot shows an essentially smooth transition from light to dark gray regions in the region of interest.

[0202] More specifically, a digital photograph is taken of the region of interest. The region of interest is preferably a plate prepared from the body, perpendicular to the intermediate region of powders A and B. The photograph can be taken using a light source transmitted through the plate, for example, by placing the plate on a light table. The pixels of the photograph are a local measure of the optical properties of the material and can be analyzed using image analysis software. Open File / Photo and select a line in the photograph using the "Straight" button. This line can be analyzed by using the "Plot Profile" function in the "Analysis" section. A profile of the gray values ​​is plotted, and the gradient can be observed as a flat or more jagged curve. For more detailed analysis, the profile data can be quantified and transferred for further analysis as needed.

[0203] L * a * b * Value / Translucency If desired, the light transmission and L * a * b *The value can be evaluated by the following procedure: provide a disc-shaped test specimen with a thickness of approximately 1 ± 0.05 mm and a measurement area of ​​at least 10 mm in diameter. To prepare the test specimen, the pre-sintered sample is sawed into wafers with a thickness of approximately 1.3 mm using a dry cut saw. The parallel large faces of the wafer are ground using silicon carbide abrasive paper (P2500). The ground sample is sintered in a suitable furnace to obtain a sintered sample with a thickness of 1 ± 0.05 mm. The sintered sample is measured as fired using a spectrophotometer (X-Rite Color i7, Grand Rapids, USA) in reflection mode against white and black backgrounds to obtain the opacity (contrast ratio) of the material. The translucency T is calculated according to T = 100% - opacity (percent). A higher translucency value indicates a higher light transmittance and a lower opacity.

[0204] Liquidity / Angle of Repose The flowability of a powder can be determined by measuring the angle of repose in accordance with the DIN ISO 4324 standard "Pulver und Granulate, Bestimmung des Schuttwinkels".

[0205] In this measurement, a given amount of powder is filled into a funnel with a defined outlet diameter (φ = 10 mm). After opening the outlet, the powder falls onto an acrylic glass plate with a defined diameter (φ = 100 mm). After a certain amount of powder has completely flowed out, the height of the remaining cone is measured. The angle of repose is calculated using the following formula: tan□=2xH / 100 (□=angle of repose; H=height of the cone).

[0206] The smaller the angle, the more flowable the powder. The following grades can be used to classify powders: Flow characteristics Angle of repose (unit: °) Excellent Under 30 Good 31~35 Sufficient (no flow additives required) 36-40 Medium (can stop powder flow) 41-45 Poor (need to work to make it flow) 46-55 Very bad 56~65 Insufficient over 66

[0207] material [Table 1]

[0208] Powder A Powder A (ZP-A) was a commercially available white (uncolored) zirconia powder. ZP-A had the following properties: BET surface: 8m 2 / g, particle size d50: 53 μm, powder bulk density: 1.55 g / cm 3 , angle of repose: 24°.

[0209] Powder B Powder B (ZP-B) was a commercially available zirconia powder doped with Fe (e.g., by adding an aqueous solution containing a soluble iron salt, drying, and milling the respective powder composition). ZP-B had the following properties: BET surface: 8m 2 / g, particle size d50: 52 μm, powder bulk density: 1.64 g / cm 3 , angle of repose: 23°.

[0210] Powder C Powder C (ZP-C) was a commercially available white (uncolored) zirconia powder. ZP-C had the following properties: BET surface: 8m 2 / g, particle size d50: 53 μm, powder bulk density: 1.49 g / cm 3 , angle of repose: 25°.

[0211] Powder D Powder D (ZP-D) was a commercially available white (uncolored) zirconia powder. ZP-D had the following properties: BET surface: 8m 2 / g, particle size d50: 53 μm, bulk density: 1.50 g / cm 3 , angle of repose: 23°.

[0212] Powder E Powder E (ZP-E) was a commercially available zirconia powder doped with Cr / Fe components (e.g., by adding an aqueous solution containing soluble Cr / Fe salts, drying, and milling the respective powder composition). ZP-E had the following properties: BET surface: 8m 2 / g, particle size d50: 52 μm, powder bulk density: 1.55 g / cm 3 , angle of repose: 23°.

[0213] Figure 8 shows micrographs of zirconia powders ZP-A, ZP-B, ZP-C, ZP-D, and ZP-E converted to binary format, demonstrating the predominantly spherical nature of the powder particles. Photographs were taken randomly.

[0214] Example 1 of the present invention A mold was prepared having a cavity with dimensions of 35 mm in the z direction and 25 mm in diameter.

[0215] The cone of ZP-A has a maximum height of H PA The mold was filled to a height of H = 15 mm. ZP-B was placed on top of ZP-A. PB +H PA Filled to 35mm.

[0216] A mixer unit was prepared, including a motor and a mixer shaft with a plastic mixing element. The mixing element was spiral-shaped (height: 6 mm; diameter: 6.5 mm; inclination: 6 mm). The mixer shaft and mixing element essentially corresponded to the shape of the mixer shown in Figure 1C.

[0217] The mixer unit was placed on the upper powder surface and started. The rotation speed was 600 rpm, which is equivalent to 10 rpm. The rotating mixing elements were introduced 30 mm in the z direction at a speed of 1 mm / s into the region of the volume ZP-A and immediately withdrawn at the same speed of 1 mm / s. The positions in x and y were kept constant. The rotating mixer shaft with the mixing elements was removed from the powder composition. The experimental setup is shown in Figure 5A.

[0218] The resulting powder mixture was compressed at a pressure of approximately 12 MPa for approximately 2 minutes. The compact was heat-treated at 900°C for 2 hours, and then cut at the center to obtain a plate. This plate was then heat-treated at a temperature of approximately 1,550°C for 4 minutes. An image of the cut plate is shown in Figure 9A.

[0219] observation The mixed zone in the x and y directions is limited to approximately one-third of the x and y dimensions of the block, and by using the methods described herein, a defined mixing of a small powder region within a fairly small total powder volume is achieved, thereby allowing for a smooth gradient in the region of interest. A gray value profile plot of the z-direction image through the mixed zone shows a smooth color gradient. A gray value profile plot of the z-direction photograph through the unmixed zone shows a sharp color gradient (Figure 9B).

[0220] Example 2 of the present invention A mold was prepared having a cavity with dimensions of 35 mm in the z direction and 25 mm in diameter.

[0221] The cone of ZP-A has a maximum height of H PA The mold was filled to a depth of (1.25;1.25) = 15 mm. On top of the layer of ZP-A, a layer of ZP-B was placed to a height of H PB +H PA Filled to 35mm.

[0222] A mixer unit was prepared, including a motor and a mixer shaft with a plastic mixing element. The mixing element was spiral-shaped (height: 6 mm; diameter: 6.5 mm; inclination: 6 mm). The mixer shaft and mixing element essentially corresponded to the shape of the mixer shown in Figure 1C.

[0223] The mixer unit was placed on the upper powder surface and started. The rotation speed was 600 rpm, which is equivalent to 10 rpm. Starting at the mold edge (position 1), the rotating mixing elements were introduced into the powder over a distance of 33 mm in the z direction at a speed of 1 mm / s up to the ZP-A region and immediately withdrawn at the same speed of 1 mm / s. The mixer's position was changed (position 2) to a total distance of 6 mm in the x / y directions, but the mixer remained at the mold edge. Another mixing in the z direction was performed using the same parameters as used in position 1. This was repeated 10 times to mix the periphery of the mold (positions 1–10). A smaller circuit was then adjusted, and six more mixing cycles in z were performed (positions 11–16). Finally, three more mixing cycles were performed approximately in the center (positions 17–19). The experimental setup is shown in Figure 10A. After spiral mixing of this powder composition, the rotating mixer shaft with the mixing elements was removed.

[0224] The resulting powder mixture was compressed at a pressure of approximately 82 MPa for approximately 2 minutes. This compact was heat-treated at 900°C for 2 hours, and then cut into a plate at the center. This plate was then heat-treated at a temperature of approximately 1,550°C for 4 minutes. An image of the cut plate is shown in Figure 10B.

[0225] observation The unmixed lower region of ZP-B smoothly transitioned to the unmixed upper region of ZP-A, with a middle region of mixed powders ZP-B and ZP-A. No distinct layers were observed. A profile plot of the gray values ​​of the image in the z-direction through the mixed zone shows a smooth color gradient. In Figure 10C, the photograph from Figure 10B was analyzed for gray values ​​using the software ImageJ. As can be seen from the plot, there is a smooth transition from the light gray region to the darker gray region in the region of interest.

[0226] Example 3 of the present invention A mold was prepared having a cavity with dimensions of 35 mm in the z direction and 25 mm in diameter.

[0227] The ZP-C layer is PCThe mold was filled to a height of H = 13 mm. On top of the layer of ZP-C, a layer of ZP-D was placed to a height of H PC +H PD Filled up to =13mm+15mm=28mm.

[0228] A mixer unit was prepared, including a motor and a mixer shaft with a plastic mixing element. The mixing element was spiral-shaped (height: 6 mm; diameter: 6.5 mm; inclination: 6 mm). The mixer shaft and mixing element essentially corresponded to the shape of the mixer shown in Figure 1C.

[0229] The mixer unit was placed on the upper powder surface and started. The rotation speed was 200 rpm, which is equivalent to 3.33 rpm. The rotating mixing elements were introduced 23 mm in the z direction at a speed of 1 mm / s to the ZP-D region and manually moved vertically along a spiral path from the edge of the mold to the center and back. The z position was then moved to approximately 18 mm and manually moved vertically again along a spiral path from the edge of the mold to the center and back. The z position was then moved to approximately 13 mm and manually moved vertically again along a spiral path from the edge of the mold to the center and back. The z position was then moved to approximately 8 mm and manually moved vertically again along a spiral path from the edge of the mold to the center and back. The z position was then moved to approximately 3 mm and manually moved vertically again along a spiral path from the edge of the mold to the center and back. The rotating mixer shaft with the mixing elements was removed from the powder composition.

[0230] After the mixing process, the resulting powder mixture was compressed at a pressure of approximately 200 MPa for approximately 3 minutes. This compact was then heat-treated at approximately 920°C for 2 hours, after which the center was cut to obtain a plate. This plate was then heat-treated at a temperature of approximately 1,500°C for 2 hours.

[0231] observation Similar to Inventive Example 2, the smooth transition between each region remained after sintering. The microstructure of the resulting sintered zirconia body was further analyzed by SEM (FIG. 11). The larger particles are associated with the 5.5 mol% yttria-containing zirconia material (ZP-D), and the smaller particles are associated with the 3 mol% yttria-containing material (ZP-C). As shown in the SEM images, the blending of the respective powders occurred at the microstructural level, where larger particles can be seen in the small particle regions and smaller particles can be seen in the large particle regions.

[0232] Example 4 of the present invention A mold was prepared having a cavity with dimensions of 35 mm in the z direction and 25 mm in diameter.

[0233] The ZP-A layer is H PA The mold was filled to a height of 6 mm. A layer of ZP-B was placed on top of the layer of ZP-A. PB = 28mm, height H PB +H PA Filled to 34mm.

[0234] A mixer unit was prepared, comprising a motor and a mixer shaft with plastic mixing elements. The mixing elements were blade-shaped (height: 6 mm; diameter: 6.5 mm; inclination: 6 mm). The mixer shaft and mixing elements essentially corresponded to the shape of the mixer shown in Figure 1B. The mixer unit was placed on the upper powder surface and started. The rotation speed was 300 rpm, which is equivalent to 5 rpm. The rotating mixing elements were manually introduced slowly in the z-direction into the region of the volume ZP-B and withdrawn. The rotating mixer shaft with the mixing elements was removed from the powder composition. The mixing profile is shown in Figure 12A / 12B.

[0235] The resulting powder mixture was compressed at a pressure of approximately 82 MPa for approximately 2 minutes. The compact was heat-treated at 920°C for 2 hours, and then cut into plates at the center. These plates were then heat-treated at a temperature of approximately 1,500°C for 2 hours. An image of the cut plate is shown in Figure 12C.

[0236] observation Similar to Inventive Example 2, the smooth transition between each region remained after sintering. In Figure 12D, the photograph from Figure 12C was analyzed for gray value using the software ImageJ. As can be seen from the plot, there is a smooth transition from the light gray region to the darker gray region in the region of interest.

[0237] Comparative Example 1 Inventive Example 4 was repeated except that the mixer shaft did not rotate during introduction into and removal from the powder composition.

[0238] The experimental setup is shown in Figures 13A-13C, and an image of the cut plate after the compression and sintering process is shown in Figure 13D.

[0239] observation Compared to Inventive Example 4, the sintered sample of Comparative Example 1 exhibited a less uniform and inhomogeneous color gradient. In addition to the above-described embodiments, the following aspects will be noted. (Appendix 1) 1. A method for producing a dental milling block, comprising: providing a mold having a cavity with a z-direction and an x / y-direction; The cavity has a height H 1 a step of partially filling the first powder with a volume V having an upper surface and a lower surface; P1 a filling step comprising: A height H above the first powder 2 introducing a second powder into a volume V having an upper surface and a lower surface; P2 wherein the upper surface of the first powder is in contact with the lower surface of the second powder, forming an intermediate region; providing a mixer unit having at least one rotatable mixing element; introducing the mixing element into the intermediate region in a z-direction while rotating; mixing the powder disposed in the intermediate region by rotating the mixing element; removing the mixing element from the powder while rotating the mixing element; compressing the powder; and optionally applying heat to the compressed powder; A method wherein the first powder differs from the second powder by its physical properties and / or chemical composition and / or color. (Appendix 2) 2. The method of claim 1, wherein the first powder and the second powder are characterized by an angle of repose of 15° to 35°. (Appendix 3) 3. The method of claim 1 or 2, wherein the first powder is applied in the form of a layer or a cone. (Appendix 4) The first powder and / or the second powder have the following characteristics: a) the powder particles of the powder have a predominantly spherical shape; b) 4m 2 / g~20m 2 / g BET surface, c) the powder particles of the first and second powders are agglomerates or aggregates of smaller particles; d) having a powder particle size d50 of 25 μm to 150 μm; e) 0.9 g / cm 3 ~2g / cm 3 having a bulk density of 4. The method according to any one of claims 1 to 3, characterized by the following, alone or in combination: (Appendix 5) 5. The method of any one of claims 1 to 4, wherein the powder mixed in the intermediate region spans less than 95% or less than 80% of the x / y dimension of the cavity of the mold. (Appendix 6) The at least one mixing element has a height H in the z direction during the mixing step. 2 6. The method of any one of claims 1 to 5, wherein the target is moved over a distance of less than 90% or less than 60% of the target. (Appendix 7) 7. The method of any one of claims 1 to 6, wherein the mixing step is adjusted to obtain a gradient in the powder in z direction and x / y direction with respect to its physical properties and / or chemical composition and / or color. (Appendix 8) The gradient has a height H in the z direction. 2 8. The method of any one of claims 1 to 7, wherein the number of serotonin receptors is at least 20%, or at least 40%. (Appendix 9) Powder V P1 and V P2 The method according to any one of appendices 1 to 8, wherein the volumes of the (Appendix 10) The at least one mixing element has a height H 2 Rotation speed RS 2 and the height H 1 Rotation speed RS 1 RS 1 RS 2 10. The method according to any one of appendices 1 to 9, which is different from the method according to (Appendix 11) 11. The method of any one of clauses 1 to 10, wherein the mixer unit comprises at least two independently rotatable or independently shaped mixing elements. (Appendix 12) 12. The method according to any one of claims 1 to 11, wherein the direction of rotation and / or the rotation speed of the mixing elements are individually adjustable. (Appendix 13) 13. The method according to any one of claims 1 to 12, which does not include the step of filling the cavity of the mold with an additional powder different from the first and second powders. (Appendix 14) 1. A method of making a dental restoration, comprising: A step of producing a dental milling block according to any one of appendices 1 to 13; applying heat to the compressed powder to obtain a heat-treated dental milling block; machining a dental restoration from the heat treated dental milling block; and sintering the dental restoration. (Appendix 15) 14. A kit of parts for producing a dental milling block, comprising: a mold according to any one of claims 1 to 13; a mixer unit according to any one of claims 1 to 13; and first and second powders according to any one of claims 1 to 13.

Claims

1. 1. A method for producing a dental milling block, comprising: providing a mold having a cavity with a z-direction and an x / y-direction; The cavity has a height H １ a step of partially filling the first powder to a volume V having an upper surface and a lower surface; Ｐ１ a filling step comprising: A height H above the first powder ２ introducing a second powder into the cavity to a volume V having an upper surface and a lower surface; Ｐ２ wherein the upper surface of the first powder is in contact with the lower surface of the second powder, forming an intermediate region; providing a mixer unit having at least one rotatable mixing element; rotating the mixing element to move through the second powder in a z-direction into the intermediate region; mixing the powder disposed in the intermediate region by rotating the mixing element; removing the mixing element from the powder while rotating the mixing element; compressing the powder; and optionally applying heat to the compressed powder; A method wherein said first powder differs from said second powder by its physical properties and / or chemical composition and / or color.

2. The first powder and / or the second powder have the following characteristics: a) the powder particles of the powder have a predominantly spherical shape; b) 4 m ２ / g to 20m ２ / g BET surface area, c) the powder particles of the first and second powders are agglomerates or aggregates of smaller particles; d) having a powder particle size d50 of 25 μm to 150 μm; e) 0.9 g / cm ３ ~2 g / cm ３ having a bulk density of 2. The method of claim 1, characterized by:

3. 3. The method of claim 1 or 2, wherein the powder mixed in the intermediate region spans less than 95% or less than 80% of the x / y dimension of the cavity of the mold.

4. The at least one mixing element has a height H in the z direction during the step of mixing the powder. ２ The method of any one of claims 1 to 3, wherein the object is moved over a distance of less than 90% or less than 60% of the distance of the object.

5. The at least one mixing element has a height H ２ Rotation speed RS ２ and the height H １ Rotation speed RS １ and RS １ is RS ２ The method according to any one of claims 1 to 4, which is different from

6. 1. A method of making a dental restoration, comprising: a step of producing a dental milling block according to any one of claims 1 to 5; applying heat to the compressed powder to obtain a heat-treated dental milling block; machining a dental restoration from the heat treated dental milling block; and sintering the dental restoration.

7. 6. A kit of parts for producing dental milling blocks, comprising: a mold according to any one of claims 1 to 5; a mixer unit according to any one of claims 1 to 5; and first and second powders according to any one of claims 1 to 5.

Images