EP4010299A1

EP4010299A1 - Method of manufacturing a zirconium dioxide green body with color and translucency gradients

Info

Publication number: EP4010299A1
Application number: EP20750275.8A
Authority: EP
Inventors: Michael GÖDIKER; Eva Kolb; Christian Strasser
Original assignee: Vita Zahnfabrik H Rauter GmbH and Co KG
Current assignee: Vita Zahnfabrik H Rauter GmbH and Co KG
Priority date: 2019-08-08
Filing date: 2020-08-05
Publication date: 2022-06-15
Also published as: WO2021023788A1; WO2021023791A1; JP2022544088A; US20220289632A1; US20220273403A1; EP4010300A1; JP2022543125A

Abstract

The invention relates to a method of manufacturing a ceramic molding, comprising the following steps: a) providing three or more ceramic powder layers that are arranged in layers, one on top of the other, b) compacting the ceramic powder layers that are arranged in layers, one on top of the other, to form a compression-molded element and sintering the compression-molded element obtained in step b) to form a ceramic molding, characterized in that the ceramic powder layers have different compositions, each ceramic powder layer comprising a mixture of at least two different base powders and each base powder containing at least 80 wt.% ZrO2 and at least 0.02 wt.% Al2O3, each weight amount being relative to the total weight of the constituents of the base powder.

Description

PROCESS FOR MANUFACTURING A ZIRCONIUM DIOXIDE BLOCK WITH COLOR

AND TRANSLUCENCY FLOW

The present invention relates to a method for producing a ceramic molded body, a ceramic molded body obtainable by the method according to the invention, and its use as dental restorations.

A wide variety of organic polymer materials and ceramic materials are known for dental dental restorations. Ceramic materials usually have a higher strength, but are more demanding to process for dental restorations when it comes to their precisely fitting manufacture. For ceramic dental restorations, both glass-ceramic and oxide-ceramic materials have established themselves on the market. Melting processes are usually used in the manufacture of glass ceramics, while powder technology pressing and sintering processes are required for oxide ceramic materials.

In the prior art, multilayer blocks made of feldspar or leucite ceramics for the dental CAD-CAM application are known. From an aesthetic point of view, these correspond to the appearance of natural teeth, but usually have a strength in the range of 150-200 MPa. However, these strengths are less suitable, particularly when it comes to dental restorations with thin walls. On the other hand, high strengths can be achieved with layered zirconia blocks. However, these are usually too opaque to be used as monolithic dental restorations. The use of high-strength zirconium dioxide restorations therefore requires manual post-processing. This can consist in infiltrating the porous frameworks with colored liquids before sintering or the sintered restorations with stains or veneering ceramics are individually adapted in color to the natural tooth color.

A particular challenge of dental restorations is to create a natural-looking color gradient in the ceramic restoration. At the same time, high demands are placed on dental restorations with regard to their strength, especially their edge strength, their translucency and machinability.

It has surprisingly been found that the problems identified in the prior art can be solved by the present invention. In particular, it has been found that a system comprising a few base powders can be used to create a continuous color gradient in ceramic moldings, in which both the translucency and the strength of the end product can be individually adjusted.

One object of the present invention is a method for producing a sintered shaped body with a color gradient for use in the production of dental restorations, comprising the steps: a) mixing at least three different base powders for producing ceramic powder layer mixtures, b) layering the ceramic obtained in step a) Powder layer mixtures to at least 5 ceramic powder layers arranged one above the other, each powder layer differing from one another; c) pressing the ceramic powder layers arranged one on top of the other to form a press mold body; and d) sintering the molded body obtained in step c) to form a ceramic molded body, each ceramic powder layer comprising a mixture of at least three different base powders and the base powders each at least 80% by weight Zr0 ₂ and at least 0.02 to 0.1 % By weight Al ₂ 0 ₃ , preferably 0.02 to 0.08% by weight Al ₂ 0 ₃ , the weight data in each case being based on the total weight of the constituents of the base powder.

Preferred embodiments of the present invention are set out in the dependent claims.

In the context of the present invention, a ceramic powder layer consists of at least three base powders which can be distinguished from one another. In particular, the powder layers consist of at least 3 or 4 distinguishable base powders, the ceramic powder layer preferably being a homogeneous one Mixture of the base powder is present. The ceramic powder layers are arranged in layers on top of one another, the respectively adjacent powder layers differing in terms of their chemical composition and / or their physical properties. The differences in the compositions of the individual powder layers can be made through the choice and amount of suitable base powder. The ceramic powder layers therefore comprise at least three different base powders. In one embodiment, at least two, preferably at least three, and in particular all ceramic powder layers comprise the same base powder, but in different amounts. It has been shown that, with a limited number of suitable base powders, a modular system can be set up with which the properties, in particular the color, the translucency and physical properties of each individual ceramic powder layer can be set. In addition to the ceramic components, the ceramic powder layers usually also have organic components, such as pressing aids. However, the proportion, if any, is limited and should not exceed 10% by weight, based on the ceramic powder layer.

In a preferred embodiment, one or more of the ceramic powder layers, in particular each ceramic powder layer, preferably has at least three base powders, preferably four base powders.

It has been found to be advantageous that four or five ceramic powder layers are provided which each differ in terms of their composition. In particular with 5 or more than 5 ceramic powder layers, a good color transition and property transition can be achieved, which is important for dental restorations. In particular, the artificial tooth necks, which are designed in deeper and darker colors, can be adjusted to the lighter incisal and dentin areas of artificial teeth, thereby taking into account the aesthetic and mechanical requirements.

In a particularly preferred embodiment, at least five powder layers are provided in step a) of the method according to the invention, each powder layer having four different base powders, but different amounts of the respective base powders being present in each powder layer. It has surprisingly been found to be particularly effective and it can be operated inexpensively if each ceramic powder layer has four or more base powders. The present invention therefore also relates to a ceramic powder layer which comprises four or more base powders.

In a preferred embodiment of the present invention, each ceramic powder layer of the molded body has one or more coloring metal oxides. In a further embodiment, the concentration of the coloring metal oxides differs in each powder layer. Each intermediate layer, that is to say each powder layer which is adjacent by two directly adjacent powder layers (neighboring layers), is preferably surrounded by a neighboring layer which has a higher concentration of coloring metal oxides than the intermediate layer. Each intermediate layer is preferably surrounded by an adjacent layer which has a lower concentration of coloring metal oxides. Each intermediate layer is particularly preferably surrounded by an adjacent layer which has a lower concentration of coloring metal oxides and a neighboring layer which has a higher concentration of coloring metal oxides.

In a preferred embodiment of the invention, the molded body has powder layers in which, starting from an outer powder layer, the concentration of one or more coloring metal oxides increases in layers. This has the particular advantage that a flowing color gradient can be set. In a further preferred embodiment of the invention, one or more of the ceramic powder layers of the molded body, preferably all powder layers, contain coloring metal oxides in an amount of 0.1 to 2.5% by weight, particularly preferably 0.2 to 2.2% by weight .-% and especially from 0.2 to 1.5% by weight, based in each case on the total weight of the powder layer.

In a preferred embodiment, the molded body has powder layers in which, starting from an outer powder layer, the concentration of at least one coloring metal oxide increases, preferably up to the opposite outer layer.

In a preferred embodiment of the present invention, each ceramic powder layer of the molded body has Fe ₂ O. In another

Embodiment, the concentration of Fe ₂ 0 ₃ differs in each

Powder layer. Every intermediate layer, that is to say every powder layer, is preferred is adjacent by two directly adjacent powder layers (neighboring layers), surrounded by a neighboring layer which has a higher concentration of Fe ₂ O than the intermediate layer. Each intermediate layer is preferably surrounded by a neighboring layer which has a lower concentration of Fe ₂ O ₃ . Particularly preferably, each intermediate layer is surrounded by a neighboring layer which has a lower concentration of Fe ₂ O ₃ and a neighboring layer which has a higher concentration of Fe ₂ O ₃ .

In a preferred embodiment of the invention, the molded body has powder layers in which the concentration of Fe ₂ O ₃ increases in layers starting from an outer powder layer. This has the particular advantage that a flowing color gradient can be established. In a further preferred embodiment of the invention, one or more of the ceramic powder layers of the press mold body, preferably all powder layers, contain Fe ₂ O ₃ in an amount of 0.01 to 0.25% by weight, particularly preferably from 0.02 to 0 , 2% by weight and especially from 0.1 to 0.18% by weight, based in each case on the total weight of the powder layer.

In a preferred embodiment of the present invention, each ceramic powder layer of the press mold body has Er ₂ 0 ₃ . In a further embodiment, the concentration of Er ₂ 0 ₃ differs in each powder layer. Each intermediate layer, that is to say each powder layer which is adjacent by two directly adjacent powder layers (neighboring layers), is preferably surrounded by a neighboring layer which has a higher concentration of Er ₂ O ₃ than the intermediate layer. Each intermediate layer is preferably surrounded by an adjacent layer which has a lower concentration of Er ₂ O ₃ . It is particularly preferable for each intermediate layer to be surrounded by a neighboring layer which has a lower concentration of Er ₂ 0 ₃ and a neighboring layer which has a higher concentration of Er ₂ 0 ₃ .

In a preferred embodiment of the invention, the molded body has powder layers in which, starting from an outer powder layer, the concentration of Er ₂ O ₃ increases in layers. This has the particular advantage that a flowing color gradient can be established. In a further preferred embodiment of the invention, one or more of the ceramic powder layers of the molded body, preferably all powder layers, have Er ₂ 0 ₃ in an amount of 0.01 to 1.5% by weight, particularly preferably from 0.05 to 1, 2 % By weight and especially from 0.1 to 0.9% by weight, or 0.2 to 0.5% by weight, in each case based on the total weight of the powder layer.

In a further preferred embodiment, one or more of the powder layers, preferably each powder layer, of the molded body have Co 0 ₄ . The amount of Co ₃ O ₄ can usually be in the range from 0.001 to 0.01, particularly preferably from 0.002 to 0.08% by weight and especially from 0.003 to 0.006% by weight, based in each case on the total weight of the powder layer .

The base powders of the present invention each comprise at least 80% by weight of Zr0 ₂ and at least 0.02% by weight of Al ₂ 0 ₃ , the weight data in each case being based on the total weight of the components of the base powder. In a preferred embodiment of the present invention, the base powders comprise Al ₂ O ₃ in an amount of 0.02 to 0.6% by weight, particularly preferably 0.03 to 0.4% by weight and especially 0.04 to 0 , 2 or 0.003 to 0.1 or 0.02 to 0.08% by weight, based in each case on the total weight of the base powder. The base powders are suitable for the production of dental restorations and therefore have the necessary biocompatibility requirements even in the final sintered state. The high proportion of zirconium dioxide, which is preferably stabilized by yttrium oxide, also ensures high strength of the final sintered ceramics. The base powders are chosen so that they are matched to one another with regard to their grain sizes and their sintering behavior, so that sintering defects do not occur during sintering. By mixing the base powders, an individual coloring and translucency can be achieved in each ceramic powder layer, which in turn is selected in such a way that it leads to a continuous and stepless color gradient with the adjacent powder layers, if any.

The presence of yttrium oxide or erbium oxide is advantageous for phase stabilization of the zirconium dioxide ceramics in the sintered state.

In a preferred embodiment, at least one, preferably at least two or three of the base powders, in particular all base powders, comprise yttrium oxide (Y ₂ 0 ₃ ) and / or erbium oxide (Er ₂ 0 ₃ ), preferably in an amount of at least 3% by weight, in particular of at least 5% by weight or at least 6% by weight and in particular from 4.5 to 11% by weight, especially from 6 to 10% by weight, in each case based on the total weight of the constituents of the base powder. In one embodiment of the present invention, at least one of the base powders, preferably at least two or at least three of the base powders, has coloring metal oxides. For example, these coloring metal oxides can be selected from the group consisting of iron oxide (Fe ₂ 0 ₃ ), cobalt oxide (C03O4) and erbium oxide (Er ₂ 0 ₃ ). Individual tooth colors can be created by adding the coloring metal oxides. By mixing several base powders in each ceramic powder layer, a defined, coordinated material can be obtained.

In one embodiment of the present invention, at least one of the base powders, preferably at least two or at least three of the base powders, contains zirconium dioxide, optionally together with hafnium dioxide, in an amount of at least 89% by weight, preferably in an amount of 89 to 98% by weight , in particular from 90 to 96% by weight, each based on the total weight of the constituents of the base powder.

In one embodiment, the base powder can be zirconium dioxide (Zr0 ₂ ) and hafnium dioxide (Hf0 ₂ ), preferably in a weight ratio of Zr0 ₂ to Hf0 ₂ of 25: 1 to 98: 1, in particular 30: 1 to 90: 1 and especially 50: 1 up to 90: 1.

In a preferred embodiment, the powder layers contain a base powder

A. which contains 92 to 96 wt% zirconia, 0.02 to 0.1 wt% alumina, 3.5 to 6.5 wt% or 5.0 to 9.5 wt% yttria and 0.02 to 0.1% by weight of cobalt oxide, the weight data being based in each case on the total weight of the base powder A.

In a further preferred embodiment, the powder layers have a base powder B which contains 85 to 93% by weight of zirconium dioxide, 0.02 to 0.1% by weight of aluminum oxide and 7.5 to 11% by weight of erbium oxide, the Weight data are based on the total weight of the base powder

B.

In a further embodiment, the powder layers have a base powder C which contains 90 to 94% by weight of zirconium dioxide, 0.02 to 0.1% by weight of aluminum oxide and 5.5 to 8.0% by weight or 6.5 to Contains 9.5% by weight of yttrium oxide, the weight data being based in each case on the total weight of the base powder

C. In a further preferred embodiment of the present invention, the powder layers have a base powder D which contains 90 to 94% by weight of zirconium dioxide, 0.02 to 0.1% by weight of aluminum oxide, 5.5 to 8.0% by weight or 6.5 to 9.5% by weight of yttrium oxide and 0.1 to 0.3% by weight of iron oxide, the weight data in each case being based on the total weight of the base powder D.

In a further embodiment of the present invention, at least one base powder, preferably all base powders, additionally contain organic constituents, preferably in an amount of 3 to 6% by weight, in particular in an amount of 4 to 5% by weight. Particularly suitable organic constituents are binders and pressing aids, which can be easily removed thermally in the debinding step. Suitable binders for zirconium dioxide sintering powder are known to the person skilled in the art. This includes, for example, polyvinyl alcohol (PVA).

The base powders preferably have a bulk density below 1.2 g / cm ³ .

It has proven to be advantageous to use base powders which have an average granulate size D ₅₀ of 35 μm to 85 μm, preferably 40 μm to 80 μm and in particular 50 μm to 70 μm or 40 to 60 μm. The granulate powders are measured dry using laser diffraction using a Cilas granulometer.

The inorganic constituents of the base powder, that is to say after removal of the organic constituents such as binders, etc., usually have a particle size D ₅₀ of 0.1 to 1 μm, preferably 0.2 μm to 0.8 μm and in particular 0.2 pm to 0.7 pm, measured by means of laser diffraction. It was found that the particle sizes make a positive contribution to sintering and in particular to the color transitions between the individual powder layers.

In a particularly preferred embodiment of the present invention, five ceramic powder layers are arranged in layers one above the other in step b). The layers can be arranged, for example, in a cylindrical container with the formation of slices or disks. Usually, the powder layers can be pressed uniaxially after each layer application. This can be done, for example, by a press ram, but only pre-consolidation takes place. The uniaxial pressing of the layers perpendicular to the The layer surface is preferably carried out at a pressure of 10 to 20 MPa, in particular 12 to 15 MPa.

More preferably, the pressing in step c) is initially carried out uniaxially and perpendicular to the layer surface, preferably with the formation of a pre-compressed molded body with a density below 2.8 g / cm ³ , preferably with a density in the range from 2.5 to 2.75 g / cm ³ , e.g. 2.65 g / cm ³ . The uniaxial pre-compaction can lead to a better and more intimate mixing and thus a more even transition between the layers.

In a further embodiment of the method according to the invention, the pressing in step c) takes place isostatically, the isostatic pressing preferably taking place after uniaxial pre-compression, with the formation of a molded body with a density (green compact density) below 3.4 g / cm ³ , in particular one Density of 2.80 to 3.15 g / cm ³ , especially with a density of 2.85 to 3.10 g / cm ³ . The isostatic pressing is preferably carried out after all layers of the compression molding have been arranged. Suitable pressures for isostatic pressing are usually in the range from 500 to 10,000 bar, preferably in the range from 800 to 8000 bar, for example 1000 to 7000 bar or 1000 to 3000 bar.

The thicknesses of the individual powder layers of the molded body can vary. In a preferred embodiment, at least two of the ceramic powder layers differ in terms of their thickness. At least two of the ceramic powder layers of the molded body preferably have a thickness difference of at least 5%. Typically, the molded bodies can be in the form of cylindrical, circular disks with diameters in the range from 50 to 200 mm, for example 75 to 150 mm. The total thickness of the cylindrical disks can for example be in the range from 8 to 40 mm, preferably from 10 to 30 mm, especially from 13 to 25 mm. The dimensions relate to the molded body in the unsintered state.

With regard to the color design and the subsequent processing, it has been found to be advantageous that at least one of the outer ceramic

Powder layers, preferably both outer ceramic powder layers of the

Press-molded body, has / have a greater thickness than a ceramic powder layer lying between the outer ceramic powder layers. In particular when using the ceramic moldings produced according to the invention for the production of dental restorations, the above-described layer structure with at least one thicker outer layer has proven to be advantageous, since this represents a suitable structure for processing in CAD / CAM systems or other subtractive processing methods.

In a particularly preferred embodiment of the present invention, five ceramic powder layers are arranged in step b) of the method according to the invention, the first powder layer 20 to 30%, preferably 22 to 28%, the second powder layer 10 to 20%, preferably 12 to 18%, the third powder layer makes up 15 to 25%, preferably 17 to 23%, the fourth powder layer 10 to 20%, preferably 12 to 18% and the fifth powder layer 20 to 30%, preferably 22 to 28% of the total thickness of the powder layers arranged one above the other the stipulation that the total thickness is 100%.

In a further embodiment of the present invention, the sintering in step d) of the method according to the invention takes place at a temperature in the range from 950 to 1100 ° C., preferably from 980 to 1050 ° C., with the formation of a pre-sintered ceramic shaped body (white body). The sintering usually takes place over a period of time which is sufficient to remove the binders present and to give the molded body sufficient strength for processing by subtractive methods. The pre-sintered and debonded molded bodies are referred to as white bodies. The white body density is preferably in a range from 3.15 to 3.35 g / cm ³ , in particular in the range from 3.2 to 3.3 g / cm ³ . These density ranges have proven to be particularly advantageous in terms of high edge stability and low tool wear.

In one embodiment, the sintering in step d) of the method according to the invention for producing the white body takes place over a period of more than 30 minutes, preferably more than 1 hour, in particular more than 20 hours or more than 50 hours, for example 60 to 200 hours or 70 to 150 hours.

In particular for the production of ceramic dental restorations, it is advisable that the pre-sintered ceramic shaped body in step d) be subtractive

Process is processed and preferably then in a further io Step is final sintered. When using subtractive methods, the sintering shrinkage is usually taken into account.

It has been shown, surprisingly, that an optimal setting of the surface hardness in the layer composite can be set with the aid of the method according to the invention. A lower hardness can thus be set in the cutting area of a dental restoration than, for example, in the tooth neck area. In a preferred embodiment of the present invention, the Vickers hardness of one outer layer differs from the Vickers hardness of the opposite outer layer. The difference in Vickers hardness is preferably at least 5%, more preferably at least 10%, in particular at least 15% or at least 20%, each based on the outer layer with the lower hardness.

The Vickers hardness [HV2] according to DIN EN 843 of the outer layer with the lower Vickers hardness is 45 to 60, particularly preferably from 50 to 59. The Vickers hardness [HV2] according to DIN EN 843 of the outer layer with the higher Vickers hardness is preferably above 60 and especially in the range from 61 to 80, particularly preferably from 65 to 75.

The final sintering usually takes place at temperatures above 1350 ° C, preferably above 1400 ° C, especially in the range from 1420 ° C to 1600 ° C or 1450 ° C to 1550 ° C.

The sintering time for the final sintering usually takes place over a period of more than 4 minutes, preferably more than 5 minutes, in particular in the range from 5 to 120 minutes.

The present invention also provides a ceramic shaped body obtainable by the process according to the invention.

The ceramic moldings according to the invention can be used in particular in the dental field. Here they are characterized by high edge strength in dental restorations, an excellent structure and high 3-point flexural strength. The ceramic molded bodies of the present invention are therefore preferably dental restorations, such as, for example, inlays, onlays, crowns, bridges, veneers and veneers or abutments for implants. Another object of the present invention is the use of the ceramic molded body according to the invention for dental restorations or for the production of dental restorations.

Examples:

Table 1 shows 4 base powders A to D which are used for the compositions of the ceramic powder layers. The granulate size D _{50 of} the base powder is in the range of 40-80 μm. The inorganic constituents of the base powder have a particle size D ₅₀ of 0.2 to 0.7 μm.

The weight data relate in each case to the total weight of the powder composition.

Table 1

The arrangements of the layers listed in Table 2 below show the composition of each individual ceramic powder layer in the molded body. The molded bodies are intended for use in the production of dental restorations, so that the layer compositions are designed according to the position in the tooth. The compositions of the Powder layers are formed from the base powders by varying the proportions in order to obtain an ideal color gradient. The composition of each powder layer is achieved by homogeneously mixing the base powders in the specified amounts. The powders are then placed in layers in a cylindrical press mold with a diameter of 100 mm and a layer thickness of 18 mm is set. The powder layers are pre-pressed uniaxially at a pressure of 13 MPa perpendicular to the layer surface and then isostatically pressed at a pressure of 2000 bar.

This is followed by debinding at approx. 1000 ° C over a period of approx. 100 hours. The whites obtained in this way are milled into dental restorations using CAD / CAM systems.

These pre-sintered and processed white bodies are then finally sintered at 1450 ° C. for a period of 120 minutes.

Table 2

In the present example, the ceramic powder layers are arranged so that layer 1 (cutting edge) 25%, layer 2 (dentin / cutting edge) 15%, layer 3 (dentin) 20%, layer 4 (dentin / neck) 15% and layer 5 ( Neck) makes up 25% of the total thickness of the die body.

FIGS. 1 and 2 show, by way of example, dental restorations that are obtained from the exemplary ceramic molded body.

The layer transitions and color transitions are fluid. The restorations show excellent edge strength and stability. Reworking and readjusting the tooth color is not necessary.

The optimal structure and the composition of the layers show a largely homogeneous shrinkage across all layers during the

Sintering. This is particularly important for a precisely fitting production of the dental Restorations are an advantage because extensive reworking can be avoided as far as possible.

Surprisingly, it was found that the hardness of the ceramic can be optimally adjusted through the layer structure. For this purpose, the Vickers hardness is measured after furnace firing on the top (light layer, cutting edge) and on the bottom (dark layer, tooth neck) of an exemplary disc. With regard to the exemplary embodiment, the white body density and thus also the Vickers hardness on the underside is always greater than on the top.

The following table 3 shows the Vickers hardness values [HV2] determined in accordance with DIN EN 843:

Table 3:

Claims

1. A method for producing a sintered shaped body with a color gradient for use in the production of dental restorations, comprising the steps: a) mixing at least three different base powders for producing ceramic powder layer mixtures, b) layering the ceramic powder layer mixtures obtained in step a) in at least 5 one above the other ordered ceramic powder layers, each powder layer being different from one another; c) pressing the ceramic powder layers arranged one on top of the other to form a press mold body; and d) sintering the molded body obtained in step c) to form a ceramic molded body, each ceramic powder layer comprising a mixture of at least three different base powders and the base powders each at least 80% by weight Zr0 ₂ and at least 0.02 to 0.1 % By weight Al ₂ 0 ₃ , the weight data being based in each case on the total weight of the constituents of the base powder.

2. The method according to claim 1, characterized in that at least one, preferably at least 2 or at least 3 of the base powders, in particular all of the base powders Y ₂ 0 and / or Er ₂ 0 ₃ , preferably in an amount of at least 3 wt .-%, in particular of at least 5% by weight or at least 6% by weight and in particular from 4.5 to 11% by weight, especially from 6 to 10% by weight, based on the total weight of the constituents of the base powder.

3. The method according to claim 1 or 2, characterized in that at least one of the base powders, preferably at least 2 or at least 3 of the base powders, has coloring metal oxides.

4. The method according to one or more of claims 1 to 3, characterized in that at least one of the base powders, preferably at least 2 or at least 3 of the base powder, zirconium dioxide and / or hafnium oxide in an amount of at least 89% by weight, preferably in an amount of 89 to 98% by weight, in particular 90 to 96% by weight, each based on the total weight of the ingredients of the base powder.

5. The method according to one or more of claims 1 to 4, characterized in that each ceramic powder layer comprises at least 3 base powders, preferably 4 base powders.

6. The method according to one or more of claims 1 to 5, characterized in that 5 powder layers are provided which each have 4 different base powders in different amounts.

7. The method according to one or more of claims 1 to 6, characterized in that the powder layers contain a base powder A containing 92 to 96 wt .-% zirconium dioxide, 0.02 to 0.1 wt .-% Al ₂ 0 ₃ , 3 , 5 to 6.5% by weight Y ₂ 0 ₃ and 0.02 to 0.1% by weight Co ₃ 0 ₄ , the weight data in each case being based on the total weight of the base powder A.

8. The method according to one or more of claims 1 to 7, characterized in that the powder layers contain a base powder B, containing 85 to 93 wt .-% zirconium dioxide, 0.02 to 0.1 wt .-% Al ₂ 0 ₃ and 7 .5 to 11.0% by weight of Er ₂ 0 ₃ , the weight data in each case being based on the total weight of the base powder B.

9. The method according to one or more of claims 1 to 8, characterized in that the powder layers contain a base powder C containing 90 to 94 wt .-% zirconium dioxide, 0.02 to 0.1 wt .-% Al ₂ 0 ₃ and 5 , 5 to 8.0% by weight Y ₂ 0 ₃ , the weight data in each case being based on the total weight of the base powder C.

10. The method according to one or more of claims 1 to 9, characterized in that the powder layers contain a base powder D containing 90 to 94 wt .-% zirconium dioxide, 0.02 to 0.1 wt .-% Al ₂ 0 ₃ , 5 , 5 to 8.0% by weight Y ₂ 0 and 0.1 to 0.3 wt .-% Fe ₂ 0, the weight data in each case being based on the total weight of the base powder D.

11. The method according to any one of the preceding claims, characterized in that at least 2 of the ceramic powder layers differ in terms of their thickness, preferably have a thickness difference of at least 5%.

12. The method according to any one of the preceding claims, characterized in that at least one of the outer ceramic powder layers, preferably both outer ceramic powder layers, has / have a greater thickness than a ceramic powder layer lying between the outer ceramic powder layers.

13. The method according to one or more of the preceding claims, characterized in that the ceramic shaped body pre-sintered in step d) is processed by subtractive methods and is preferably then finally sintered in a further step.

14. The method according to one or more of the preceding claims, characterized in that the base powders have an average granulate size D ₅₀ of 35 μm to 85 μm, preferably 40 μm to 80 μm and in particular 50 μm to 70 μm or 40 to 60 μm.

15. The method according to one or more of the preceding claims, characterized in that the inorganic constituents of the base powder average particle size D ₅₀ from 0.1 to 1 pm, preferably from 0.2 pm to 0.8 pm and in particular from 0.2 pm to 0.7 pm, measured by means of laser diffraction.

16. The method according to one or more of the preceding claims, characterized in that the concentration of Fe ₂ 0 ₃ increases in layers and preferably all powder layers, Fe ₂ 0 ₃ in an amount of 0.01 to 0.25 wt .-%, especially preferably from 0.02 to 0.2% by weight and especially from 0.1 to 0.18% by weight, each based on the total weight of the powder layer.

17. Ceramic molded body, preferably a dental restoration, obtainable by a method according to one of the preceding claims.

18. Use of the ceramic molded body according to claim 17 for dental restorations.