Process for producing a sintered compact with a color gradient for use in preparing dental restorations, sintered compact, and use of the compact

Abstract

The present invention relates to a sintered compact having a color gradient for use in the manufacture of dental restorations, which is obtained by sintering a compact containing five or more different ceramic powder layers, each powder layer containing at least two different base powders, each of which contains at least 80% by weight of zirconia (ZrO), based on the total weight of the base powders.

Description

Technical Field

[0001] The present invention relates to a sintered compact having a color gradation for use in the production of dental restorations, and to the use of a sintered compact for dental restorations.

Background Art

[0002] Dental restorations are known in both a wide variety of organic polymer materials and ceramic materials. Ceramic materials generally have higher strength, but are more difficult to process with respect to the tailor-made production of dental restorations. For ceramic dental restorations, both glass-ceramic and oxide ceramic materials are on the market. For the production of glass-ceramic-based dental restorations, a melting process is usually used, and for oxide ceramic materials, press working and sintering processes by powder technology are required.

[0003] In the prior art, multi-layer blocks for dental CAD-CAM applications made of feldspar or leucite-based ceramics are known. These correspond to the natural tooth appearance in terms of aesthetics, but usually have a strength in the range of 150 to 200 MPa. However, such strength is not very suitable especially for thin dental restorations. On the other hand, when using layered zirconia blocks, high strength can be achieved. However, since these are usually opaque, they cannot be used as monolithic dental restorations. Therefore, for using high-strength zirconia restorations, manual rework is required. This may include infiltrating a colored liquid into a porous framework before sintering, or individually color-matching the sintered restoration to the natural tooth color using staining or veneer ceramics.

Summary of the Invention

Problems to be Solved by the Invention

[0004] A specific problem with dental restorations is to produce a natural color gradation in ceramic restorations. At the same time, high requirements are imposed on dental restorations with respect to strength, especially their edge strength, translucency, and processability.

Means for Solving the Problem

[0005] Surprisingly, it has been found that the problems shown in the prior art can be solved by the present invention. In particular, it has been found that by using a system containing several types of base powders, a stepwise color gradation can be produced in a ceramic compact that can individually adjust both the translucency and strength of the final product.

Brief Description of the Drawings

[0006]

Figure 1

Mode for Carrying Out the Invention

[0007] In a first aspect of the present invention, it relates to a sintered compact having a color gradation for use in the production of dental restorations, obtained by sintering a compression molded body containing five or more different ceramic powder layers, each powder layer containing at least two different base powders. Each base powder contains at least 80% by weight of zirconia (ZrO 2 )), and the amount is based on the total weight of the base powder.

[0008] Within the scope of the present invention, the ceramic powder layer consists of at least two distinguishable base powders, preferably three or four distinguishable base powders, and the ceramic powder layer is preferably in the form of a homogeneous mixture of the base powders. The ceramic powder layers are preferably stacked in layers, and each adjacent powder layer has different chemical compositions and / or physical properties. The difference in the composition of the individual powder layers can be achieved by the type and amount of the appropriate base powders selected. Thus, the ceramic powder layer contains at least two different base powders. In one embodiment, at least two, preferably at least three, and in particular all, ceramic powder layers contain the same base powder, but in different amounts. It has been found that the modular system can be constructed with a limited number of suitable base powders, thereby enabling the adjustment of the properties of the individual ceramic powder layers, particularly color, translucency, and physical properties. In addition to the ceramic components, the ceramic powder layer usually contains organic components such as pressing additives. However, the proportion is limited and should not exceed 10% by weight based on the ceramic powder layer.

[0009] In a preferred embodiment, one or more ceramic powder layers, particularly each ceramic powder layer, preferably contain at least three base powders, preferably four base powders. In particular, sintering a compression molded body containing five or more different ceramic powder layers used in accordance with the present invention exhibits certain advantages. In particular, by using five or more ceramic powder layers, it is possible to achieve a good color gradient and a physical property gradient that are important for dental restorations. Thus, in particular, an artificial tooth neck designed in a darker color can be adjusted by a gradual transition to the brighter tip and dentin region of the artificial tooth, satisfying aesthetic and mechanical requirements.

[0010] In a particularly preferred embodiment, the sintered compact according to the invention has five powder layers, each powder layer containing four different base powders, but each powder layer containing different amounts of each base powder. Surprisingly, it has been found that when each ceramic powder layer contains four or more base powders, it may be possible to perform the operation particularly effectively and inexpensively. Therefore, the present invention further relates to a ceramic powder layer containing four or more base powders.

[0011] The base powders used according to the invention each contain at least 80% by weight of zirconia (ZrO 2 ), preferably at least 0.02% by weight of Al 2 O 3 , and the amounts are each based on the total weight of the components of the base powder.

[0012] In a preferred embodiment of the present invention, each ceramic powder layer of the compression molded body contains one or more colored metal oxides. In another embodiment, the concentration of the colored metal oxide is different in each powder layer. Preferably, each intermediate layer, i.e., each powder layer bounded by two directly adjacent powder layers (adjacent layers), is surrounded by adjacent layers containing a higher concentration of colored metal oxides compared to the intermediate layer. Preferably, each intermediate layer is surrounded by adjacent layers containing a lower concentration of colored metal oxides. More preferably, each intermediate layer is surrounded by one adjacent layer with a lower concentration of colored metal oxides and one adjacent layer with a higher concentration of colored metal oxides.

[0013] In a preferred embodiment of the present invention, the compression molded body contains powder layers in which the concentration of one or more colored metal oxides increases layer by layer starting from the outer powder layer. In particular, this has the advantage of being able to create a stepwise color gradation. In another preferred embodiment of the present invention, one or more ceramic powder layers of the compression molded body, preferably all powder layers, contain colored metal oxides in an amount of 0.1 to 2.5% by weight, more preferably 0.2 to 2.2% by weight, particularly 0.2 to 1.5% by weight, and each amount is based on the total weight of the powder layer.

[0014] In a preferred embodiment, the compression molded body includes a powder layer that proceeds from the outer powder layer and in which the concentration of at least one colored metal oxide increases layer by layer, preferably all the way to the outer layer on the opposite side.

[0015] In a preferred embodiment of the present invention, each ceramic powder layer of the compression molded body contains Fe 2 O 3 . In another embodiment, the concentration of Fe 2 O 3 is different in each powder layer. Preferably, each intermediate layer, i.e., each powder layer bounded by two directly adjacent powder layers (adjacent layers), is surrounded by one adjacent layer containing a higher concentration of Fe 2 O 3 compared to the intermediate layer. Preferably, each intermediate layer is surrounded by one adjacent layer containing a lower concentration of Fe 2 O 3 . More preferably, each intermediate layer is surrounded by one adjacent layer with a lower concentration of Fe 2 O 3 and one adjacent layer with a higher concentration of Fe 2 O 3 .

[0016] In a preferred embodiment of the present invention, the compression molded body includes a powder layer in which the concentration of Fe 2 O 3 increases layer by layer as it progresses from the outer powder layer. In particular, this has the advantage of being able to create a stepwise color gradation. In another preferred embodiment of the present invention, one or more ceramic powder layers of the compression molded body, preferably all the powder layers, contain Fe 2 O 3 in an amount of 0.01 to 0.25% by weight, more preferably 0.02 to 0.2% by weight, particularly 0.1 to 0.18% by weight, and each amount is based on the total weight of the powder layer.

[0017] In a preferred embodiment of the present invention, each ceramic powder layer of the compression molded body contains Er 2 O 3 . In another embodiment, Er 2 O 3The concentration is different in each powder layer. Preferably, each intermediate layer, i.e., each powder layer bounded by two directly adjacent powder layers (adjacent layers), has a higher concentration of Er compared to the intermediate layer. 2 O 3 is surrounded by one adjacent layer containing 2 O 3 . Preferably, each intermediate layer is surrounded by one adjacent layer containing a lower concentration of Er 2 O 3 . More preferably, each intermediate layer is surrounded by one adjacent layer with a lower concentration of Er 2 O 3 and one adjacent layer containing a higher concentration of Er

[0018] In a preferred embodiment of the present invention, the compression molded body contains powder layers in which the concentration of Er 2 O 3 increases from layer to layer as it progresses from the outer powder layer. In particular, this has the advantage of being able to create a stepwise color gradation. In another preferred embodiment of the present invention, one or more ceramic powder layers of the compression molded body, preferably all powder layers, contain Er in an amount of 0.01 to 1.5 wt%, more preferably 0.05 to 1.2 wt%, particularly 0.1 to 0.9 wt%, or 0.2 to 0.5 wt%, and each amount is based on the total weight of the powder layer. 2 O 3

[0019] In another preferred embodiment, one or more powder layers of the compression molded body, preferably each powder layer, contain Co 3 O 4 . Usually, the amount of Co 3 O 4 may be in the range of 0.001 to 0.01, more preferably 0.002 to 0.08 wt%, particularly 0.003 to 0.006 wt% based on the total weight of the powder layer.

[0020] The base powder is suitable for the production of dental restorations and meets the requirements of biocompatibility even in the sintered state. Since it is preferable that the ratio of zirconia is high and it is stabilized by yttria, the strength of the finally sintered ceramic is further increased. The base powders are selected to match each other in terms of crystal grain size and sintering behavior so that no sintering voids occur during sintering. The mixing of the base powders can achieve individual coloring and translucency in each ceramic powder layer, which is selected to provide a continuous and gradual color gradation when there are adjacent powder layers.

[0021] In a preferred embodiment of the present invention, the base powder contains Al in an amount of 0.02 to 0.6% by weight, more preferably 0.03 to 0.4% by weight, particularly 0.04 to 0.3% by weight, preferably 0.04 to 0.2% by weight, or 0.03 to 0.1% by weight, or particularly 0.02 to 0.08% by weight. 2 O 3 where each amount is based on the total weight of the powder layer.

[0022] The presence of yttria or erbium oxide is advantageous for the phase stabilization of zirconia-based ceramics in the sintered state.

[0023] In a preferred embodiment, at least one, preferably at least two or three, particularly all of the base powders contain yttria (Y 2 O 3 ) and / or erbium oxide (Er 2 O 3 ) in an amount of preferably at least 3% by weight, particularly at least 5% by weight, or at least 6% by weight, particularly 3.0 to 11% by weight, particularly 5 to 10% by weight, preferably 4.5 to 11% by weight, particularly 6 to 10% by weight, and the amount is based on the total weight of the components of the base powder.

[0024] In one embodiment of the present invention, at least one, preferably at least two, or at least three of the base powders contain a colored metal oxide. For example, these colored metal oxides are iron oxide (Fe 2 O3 ) Cobalt oxide (Co 3 O 4 ), erbium oxide (Er 2 O 3 ) may be selected from the group consisting of. By adding these colored metal oxides, the color of each tooth can be created. By mixing several base powders in each ceramic powder layer, a material with a defined balance can be obtained.

[0025] In an 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 zirconia, optionally together with hafnia, in an amount of at least 89% by weight, preferably from 89 to 98% by weight, particularly from 90 to 96% by weight, each amount being based on the total weight of the components of the base powder.

[0026] In one embodiment, the base powder preferably contains zirconia and hafnia in a weight ratio of ZrO 2 to HfO 2 from 25:1 to 98:1, particularly from 30:1 to 90:1, especially from 50:1 to 90:1.

[0027] In a preferred embodiment, the powder layer contains a base powder A containing 92 to 96% by weight of zirconia, 0.02 to 0.4% by weight, preferably 0.02 to 0.1% by weight of alumina, 3.5 to 6.5% by weight, or 5 to 10% by weight, preferably 5 to 9.5% by weight of yttria, and 0.02 to 0.1% by weight of cobalt oxide, the amounts being based on the total weight of the base powder A respectively.

[0028] In another preferred embodiment, the powder layer contains a base powder B containing 85 to 93% by weight of zirconia, 0.02 to 0.4% by weight, preferably 0.02 to 0.1% by weight of alumina, and 7.5 to 11% by weight of erbium oxide, the amounts being based on the total weight of the base powder B respectively.

[0029] In another embodiment, the powder layer comprises a base powder C comprising 90 to 94% by weight of zirconia, 0.02 to 0.4% by weight, preferably 0.02 to 0.1% by weight of alumina, and 5.5 to 8.0% by weight, or 6.5 to 10% by weight, preferably 6.5 to 9.5% by weight of yttria, the amounts being based on the total weight of the base powder C respectively.

[0030] In another preferred embodiment of the present invention, the powder layer comprises a base powder D comprising 90 to 94% by weight of zirconia, 0.02 to 0.4% by weight, preferably 0.02 to 0.1% by weight of alumina, 5.5 to 8.0% by weight, or 6.5 to 10% by weight, preferably 6.5 to 9.5% by weight of yttria, and 0.1 to 0.3% by weight of iron oxide, the amounts being based on the total weight of the base powder D respectively.

[0031] In another embodiment of the present invention, at least one base powder, preferably all base powders, further comprises an organic component in an amount preferably of 3 to 6% by weight, particularly 4 to 5% by weight. Suitable organic components include, in particular, binders and pressing additives that can be easily removed thermally during the debinding step. Binders suitable for zirconia sintered powders are known to those skilled in the art. These include, for example, polyvinyl alcohol (PVA).

[0032] Preferably, the base powder has a bulk density of less than 1.2 g / cm 3 It has a bulk density of less than 1.2 g / cm³.

[0033] It has been proven advantageous to use a base powder having an average particle size D50 of 35 μm to 85 μm, preferably 40 μm to 80 μm, particularly 50 μm to 70 μm, or 40 to 60 μm. The granular powder is measured in the dry state by laser diffraction using a Cilas particle size distribution analyzer.

[0034] Typically, the particle size D50 of the inorganic components of the base powder, i.e., after removing the organic components such as the binder, is from 0.1 to 1 μm, preferably from 0.2 μm to 0.8 μm, particularly from 0.2 μm to 0.7 μm when measured by laser diffraction. The particle size has been found to contribute positively to sintering, particularly to the color gradient between individual powder layers.

[0035] The compression molded body sintered according to the present invention can be obtained by stacking five or more ceramic powder layers layer by layer. The stacking of the layers can be carried out, for example, in a cylindrical container to form a disk. Usually, the uniaxial pressing of the powder layer can be carried out after the application of each layer. This can be done, for example, using a press plunger, but this only causes a preliminary compression. The uniaxial pressing of the layer perpendicular to the layer surface is preferably carried out under a pressure of 10 to 20 MPa, particularly 12 to 15 MPa.

[0036] In another preferred embodiment, the pressing of the stacked ceramic powder layers is preferably carried out to form a pre-compressed compression molded body having a density of less than 2.8 g / cm 3 in order to form a pre-compressed compression molded body having a density in the range of preferably 2.5 to 2.7 g / cm 3 , for example, having a density of 2.65 g / cm 3 . The uniaxial pre-compression can result in a better and tighter mixing state, and thus may result in a more uniform transition between the layers.

[0037] In another preferred embodiment, the pressing for preparing the compression molded body is carried out hydrostatically, and the hydrostatic pressing is preferably carried out following the uniaxial pre-compression, with a density of less than 3.4 g / cm 3 , particularly with a density in the range of 2.80 to 3.15 g / cm 3 , specifically 2.85 to 3.10 g / cm 3A compression molded body is formed with a density of. The isostatic press is preferably performed after all layers of the compression molded body are stacked. The pressure suitable for the isostatic press is usually in the range of 500 to 10,000 bar, preferably in the range of 800 to 8,000 bar, for example, in the range of 1,000 to 7,000 bar, or in the range of 1,000 to 3,000 bar.

[0038] The thicknesses of the individual powder layers of the compression molded body may be different. In a preferred embodiment, at least two of the ceramic powder layers differ in thickness. Preferably, at least two of the ceramic powder layers of the compression molded body have a thickness difference of at least 5%. Typically, the compressed molded body can be in the form of a cylindrical circular disk having a diameter in the range of 50 to 200 mm, for example, in the range of 75 to 150 mm. The total thickness of the cylindrical disk can be, for example, in the range of 8 to 40 mm, preferably in the range of 10 to 30 mm, particularly in the range of 13 to 25 mm. The dimensions relate to the compression molded body in the green state.

[0039] Regarding color design and subsequent processing, it has been proven advantageous when at least one, preferably both, of the outer ceramic powder layers of the outer ceramic powder layer of the compression molded body are thicker than the intermediate ceramic powder layers. In particular, when the ceramic molded body produced according to the present invention is used in the production of dental restorations, this is a structure suitable for processing in a CAD / CAM system or other subtractive processing methods, so a layer structure including at least one thicker outer layer as described above has been proven advantageous.

[0040] In a particularly preferred embodiment of the present invention, the compression molded body includes five ceramic powder layers. The first powder layer is 20 to 30%, preferably 22 to 28% of the total thickness of the stacked powder layers. The second powder layer is 10 to 20%, preferably 12 to 18%. The third powder layer is 15 to 25%, preferably 17 to 23%. The fourth powder layer is 10 to 20%, preferably 12 to 18%. The fifth powder layer is 20 to 30%, preferably 22 to 28%. The total thickness is 100% in total.

[0041] In another embodiment of the present invention, sintering is carried out at a temperature in the range of 950 to 1100 °C, preferably at a temperature of 980 to 1050 °C, to form a pre-sintered ceramic molded body (white body). Usually, sintering is carried out for a time sufficient to remove the existing binder, and the compression molded body is provided with sufficient strength for processing by subtractive methods. The pre-sintered and separated compression molded body is called a "white body".

[0042] In one embodiment, the sintering for forming the white body is more than 30 minutes, preferably more than 1 hour, particularly more than 20 hours, or more than 50 hours, for example, 60 to 200 hours, or 70 to 150 hours.

[0043] In particular, for manufacturing a ceramic dental restoration, it is appropriate that the pre-sintered ceramic molded body is processed by subtractive methods, preferably followed by final sintering in another step. When applying subtractive methods, usually, sintering shrinkage is considered in the calculation.

[0044] Surprisingly, it has been found that an optimal setting of the surface hardness can be achieved in the bonding layer structure using the process according to the invention. Thus, at the tip of the dental restoration, a lower hardness can be set, for example, compared to the cervical region of the tooth. In a preferred embodiment of the invention, the Vickers hardness of one outer layer is different from the Vickers hardness of the opposite outer layer. Preferably, the difference in Vickers hardness is at least 5%, more preferably at least 10%, particularly at least 15%, or at least 20% based on the outer layer with the lower hardness, respectively.

[0045] Preferably, the Vickers hardness [HV2] according to DIN EN 843 of the outer layer with the lower hardness is in the range of 45 to 60, more preferably in the range of 50 to 59. Preferably, the Vickers hardness [HV2] according to DIN EN 843 of the outer layer with the higher hardness is above 60, particularly in the range of 61 to 80, more preferably in the range of 65 to 75.

[0046] The final sintering is usually carried out at a temperature above 1350°C, preferably above 1400°C, particularly in the range of 1420°C to 1600°C, or 1450°C to 1550°C.

[0047] The sintering time of the final sintering is usually 4 minutes or more, preferably 5 minutes or more, particularly in the range of 5 to 120 minutes.

[0048] The shaped bodies according to the invention can be used particularly in the dental field. They are characterized by a high edge strength, excellent structure, and high three-point bending strength of the dental restoration. Thus, the ceramic shaped bodies of the invention are preferably dental restorations such as inlays, onlays, crowns, bridges, veneers, or abutments for implants.

[0049] The invention further relates to the use of the ceramic shaped bodies according to the invention for dental restorations or for manufacturing dental restorations.

[0050] Accordingly, the present invention further relates to a process for manufacturing a sintered compact having a color gradation for use in the manufacture of dental restorations, comprising the following steps: a) Mixing at least two, preferably at least three, different base powders to prepare five or more different ceramic powder layer mixtures; b) Stacking the different ceramic powder layer mixtures obtained in step a) to form a stacked ceramic powder layer; c) Uniaxially pressing the ceramic powder layer perpendicular to the surface of the powder layer to form a preliminarily compressed compact; d) Hydrostatically pressing the preliminarily uniaxially pressed compact obtained in step c); e) including the step of sintering the compact obtained in step d) to form a ceramic compact, wherein the ceramic powder layers each have a different composition, and each ceramic powder layer contains a mixture of at least two, preferably at least three, different base powders, and each of the base powders contains at least 80 wt% of ZrO 2 by weight, based on the total weight of the base powder.

[0051] Preferred embodiments of the process according to the invention have been described above.

[0052] The present invention further relates to a sintered compact having a layer structure and a color gradation for use in the manufacture of dental restorations, the compact comprising at least two, preferably at least three, different ceramic powder layers, each layer consisting of at least three or four different base powders, wherein each base powder contains at least 80 wt% of a ceramic oxide, by weight, based on the total weight of the base powder. Preferably, the ceramic powder layer contains a ceramic oxide as defined above. The base powders used each correspond to the base powders defined above.

Example

[0053] Table 1 shows four base powders A to D used in the composition of the ceramic powder layer. The particle size D50 of the base powder is in the range of 40 to 80 μm. The particle size D50 of the inorganic components of the base powder is 0.2 to 0.7 μm.

[0054] The amounts shown are each based on the total weight of the powder composition.

[0055] [Table 1]

[0056] The layer arrangement shown in Table 2 below indicates the composition of the individual ceramic powder layers in the compression molded body. Since the compression molded body is provided for use in the production of dental restorations, the layer composition is designed according to the position of the tooth. The composition of the powder layer is formed from the base powder by varying the ratio to obtain an ideal color gradation. The composition of each powder layer is achieved by uniformly mixing the stated amounts of the base powder. Subsequently, the powder is placed layer by layer in a cylindrical mold with a diameter of 100 mm, and the layer thickness is set to 18 mm. The powder layer is uniaxially pre-compressed under a pressure of 13 MPA perpendicular to the layer surface and then hydrostatically compressed under a pressure of 2000 bar.

[0057] Subsequently, debinding occurs at about 1000 °C over about 100 hours. The white body thus obtained is ground into a dental restoration using a CAD / CAM system.

[0058] These pre-sintered and processed white bodies are then subjected to final sintering at 1450 °C for 120 minutes.

[0059] [Table 2]

[0060] In this example, the ceramic powder layer is composed of layer 1 (tip) accounting for 25% of the total thickness of the compression molded body, layer 2 (dentin / tip) accounting for 15%, layer 3 (dentin) accounting for 20%, layer 4 (dentin / neck) accounting for 15%, and layer 5 (neck) accounting for 25%.

[0061] Figure 1 shows an example of a dental restoration obtained from an exemplary ceramic molded body.

[0062] The layer transition and color transition are smooth. The restoration shows excellent edge strength and stability. No tooth color retouching or readjustment is required.

[0063] The optimal structure and composition of the layers show substantially uniform shrinkage during sintering throughout the layers. This is advantageous for the fully conforming manufacture of dental restorations, as it can substantially avoid reprocessing where the bone breaks, in particular.

[0064] Surprisingly, it has been found that the hardness of the ceramic is optimally set by the layer structure. Thus, the Vickers hardness of an exemplary disk is measured on the upper surface (bright layer, tip) and the lower surface (dark layer, tooth neck) after firing in a kiln. For an exemplary embodiment, the density of the white body, and thus the Vickers hardness, is always greater on the lower side than on the upper side.

[0065] The determined values are shown in Table 3 below. Table 3: Vickers hardness [HV2] according to DIN EN 843 [Table 3]

Claims

1. 1. A process for producing a sintered compact with a color gradation for use in preparing a dental restoration, comprising: a) mixing at least three different base powders to prepare five or more different ceramic powder layer mixtures; b) stacking the different ceramic powder layer mixtures obtained in step a) to form a laminated ceramic powder layer including at least five different ceramic powder layers; c) uniaxially pressing the laminated ceramic powder layers perpendicularly to the upper and lower surfaces of the ceramic powder layers to form a pre-compressed compact; d) isostatically pressing the compression molded body preliminarily uniaxially pressed in step c); e) sintering the compact obtained in step d) to form a ceramic compact; each of said ceramic powder layers comprising a mixture of at least three different base powders in different amounts; At least three of the base powders comprise a coloring metal oxide selected from the group consisting of Fe2O3, Co3O4, and Er2O3; The base powders each contain at least 80% by weight of ZrO ２ the amount being based on the total weight of the base powder, the ceramic powder layer of each of the compacts comprises Er 2 O 3 ; a concentration of Er2O3 varies through each of the ceramic powder layers, and each of the ceramic powder layers, an intermediate layer, bounded by two immediately adjacent ceramic powder layers, is surrounded by one of the adjacent layers having a higher concentration of Er2O3 and one of the adjacent layers having a lower concentration of Er2O3 compared to the intermediate layer; the compact includes ceramic powder layers having an increasing concentration of Er2O3 from layer to layer proceeding from an outer ceramic powder layer; All powder layers contain 0.01 to 1.5 wt. % Er 2 O 3 , the amount being based on the total weight of the powder layer; said base powder having an average particle size D50, measured by laser diffraction, of 35 μm to 85 μm; A process wherein the inorganic component of the base powder has an average particle size D50 of 0.1 to 1 μm as measured by laser diffraction.

2. The base powders each contain at least 0.02 wt. % Al ２ O ３ 2. The process of claim 1, comprising:

3. At least one of the base powders is ２ O ３ and / or Er ２ O ３ 2. The process of claim 1, wherein the base powder comprises at least 3% by weight of the total components of the base powder.

4. At least one of the base powders is selected from zirconia and HfO ２ 2. The process of claim 1, wherein the base powder comprises at least 89% by weight of each of the components, the amount of each being based on the total weight of the components of the base powder.

5. The process of claim 1 , wherein each of the ceramic powder layers comprises at least four base powders.

6. 2. The process of claim 1, wherein the compact is comprised of five layers of the ceramic powder, each layer containing different amounts of four different base powders.

7. The ceramic powder layer is composed of 92 to 96 wt. % zirconia, 0.02 to 0.4 wt. % Al. ２ O ３ , 3.5 to 10 wt.% Y ２ O ３ %, and 0.02 to 0.1 wt. % Co ３ O ４ 2. The process of claim 1, further comprising a base powder A comprising:

8. The ceramic powder layer is composed of 85 to 93 wt. % zirconia, 0.02 to 0.4 wt. % Al. ２ O ３ and 7.5 to 11.0 wt.% Er ２ O ３ 2. The process according to claim 1, further comprising a base powder B comprising:

9. The ceramic powder layer is composed of 90 to 94 wt. % zirconia, 0.02 to 0.4 wt. % Al. ２ O ３ and 5.5 to 10 wt. % Y ２ O ３ 2. The process according to claim 1, further comprising a base powder C comprising:

10. The ceramic powder layer is composed of 90 to 94 wt. % zirconia, 0.02 to 0.4 wt. % Al. ２ O ３ and 5.5 to 10 wt. % Y ２ O ３ , 2 to 5 wt.% Fe ２ O ３ 2. The process according to claim 1, further comprising a base powder D comprising:

11. 2. The process of claim 1, wherein the compact consists of five of the ceramic powder layers, a first ceramic powder layer being 20 to 30% of the total thickness of the stacked ceramic powder layers, a second ceramic powder layer being 10 to 20%, a third ceramic powder layer being 15 to 25%, a fourth ceramic powder layer being 10 to 20%, and a fifth ceramic powder layer being 20 to 30%, totalling 100% of the total thickness of the stacked ceramic powder layers.

12. 2. The process of claim 1, wherein the pre-sintered ceramic compact is processed by a subtractive method, followed by final sintering in a separate step.

13. The uniaxial press is 2.8 g / cm ３ 2. The process of claim 1, further comprising forming a pre-compressed compact having a density of less than 1000 nm.

14. 2. The process of claim 1, wherein the uniaxial pressing is performed under a pressure of 10 to 20 MPA.

15. The isostatic pressing is performed following the preliminary uniaxial pressing and has a pressure of 2.80 to 3.15 g / cm ３ 2. The process of claim 1, further comprising forming a compact having a density of about 1000 to about 10000.

16. 2. The process according to claim 1, characterized in that the isostatic pressing is carried out under a pressure of 500 to 1000 bar.

17. Fe ２ O ３ The concentration of Fe increases from layer to layer proceeding from the outer powder layer, and all powder layers contain between 0.01 and 0.25 wt.% Fe. ２ O ３ 10. The process of claim 1, further comprising:

18. 18. A sintered compact with colour gradation for use in the manufacture of dental restorations, obtainable by the process according to any one of claims 1 to 17.

19. 20. Use of a molding according to claim 18 for a dental restoration or for preparing a dental restoration.

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