Zirconium Dioxide Green Body with Color and Translucency Gradients

Abstract

The invention relates to a sintered molding with a color gradient for use in the manufacture of dental restorations, obtainable by sintering a compression-molded element comprising five or more different ceramic powder layers, each powder layer comprising at least two different base powders and each base powder containing at least 80 wt. % ZrO.sub.2, each weight amount being relative to the total weight of the base powder.

Claims

1. A process for preparing a sintered molding with a color gradient for use in the preparation of dental restorations, comprising the steps of: a) mixing at least two different base powders; for preparing five or more different ceramic powder layer mixtures; b) stacking of the different ceramic powder layer mixtures obtained in step a) to form stacked ceramic powder layers, c) uniaxially pressing the ceramic powder layers perpendicular to the surface of the powder layer to form a preliminarily compacted compressed molding; d) isostatically pressing the compressed molding preliminarily uniaxially compacted in step c); and e) sintering the molding obtained in step d) to form a ceramic molding, wherein the ceramic powder layers respectively have different compositions, and wherein each ceramic powder layer includes a mixture of at least two different base powders, and said base powders each have at least 80% by weight ZrO.sub.2, the indicated weight being based on the total weight of the base powder.

2. The process according to claim 1, characterized in that said base powders each include at least 0.02% by weight Al.sub.2O.sub.3.

3. The process according to claim 1, characterized in that at least one of the base powders includes Y.sub.2O.sub.3 and/or Er.sub.2O.sub.3 in an amount of at least 3% by weight based on the total weight of the components of the base powder.

4. The process according to claim 1, characterized in that at least one of the base powders includes coloring metal oxides, selected from the group consisting of Fe.sub.2O.sub.3, Co.sub.3O.sub.4, and Er.sub.2O.sub.3.

5. The process according to claim 1, characterized in that at least one of the base powders includes zirconia and/or HfO.sub.2 in an amount of at least 89% by weight based on the total weight of the components of the base powder.

6. The process according to claim 1, characterized in that each ceramic powder layer includes at least 4 base powders.

7. The process according to claim 1, characterized in that the compressed molding consists of 5 ceramic powder layers that respectively include 4 different base powders in different amounts.

8. The process according to claim 1, characterized in that the ceramic powder layers include a base powder A, which contains from 92 to 96% by weight zirconia, from 0.02 to 0.4% by weight Al.sub.2O.sub.3, from 3.5 to 10% by weight Y.sub.2O.sub.3, and from 0.02 to 0.1% by weight Co.sub.3O.sub.4, the indicated weights being respectively based on the total weight of base powder A.

9. The process according to claim 1, characterized in that the ceramic powder layers include a base powder B, which contains from 85 to 93% by weight zirconia, from 0.02 to 0.4% by weight Al.sub.2O.sub.3, and from 7.5 to 11.0% by weight Er.sub.2O.sub.3, the indicated weights being respectively based on the total weight of base powder B.

10. The process according to claim 1, characterized in that the ceramic powder layers include a base powder C, which contains from 90 to 94% by weight zirconia, from 0.02 to 0.4% by weight Al.sub.2O.sub.3, and from 5.5 to 10% by weight Y.sub.2O.sub.3, the indicated weights being respectively based on the total weight of base powder C.

11. The process according to claim 1, characterized in that the ceramic powder layers include a base powder D, which contains from 90 to 94% by weight zirconia, from 0.02 to 0.4% by weight Al.sub.2O.sub.3, from 5.5 to 10% by weight Y.sub.2O.sub.3, and 2 to 5% by weight Fe.sub.2O.sub.3, the indicated weights being respectively based on the total weight of base powder D.

12. The process according to claim 1, characterized in that the compressed molding consists of 5 ceramic powder layers, wherein the first powder layer comprises from 20 to 30%, the second powder layer comprises from 10 to 20%, the third powder layer comprises from 15 to 25%, the fourth powder layer comprises from 10 to 20%, and the fifth powder layer comprises from 20 to 30%, of the total thickness of the stacked powder layers, and provided that the total thickness sums up to 100%.

13. The process according to claim 1, characterized in that the presintered ceramic molding is processed by subtractive methods.

14. The process according to claim 1, characterized in that said uniaxial pressing is effected to form a precompacted compressed molding having a density of below 2.8 g/cm.sup.3.

15. The process according to claim 1, characterized in that said uniaxial pressing is effected under a pressure of from 10 to 20 MPa.

16. The process according to claim 1, characterized in that said isostatic pressing is effected subsequently to said uniaxial precompaction, to form a compressed molding having a density of from 2.80 to 3.15 g/cm.sup.3.

17. The process according to claim 1, characterized in that said isostatic pressing is effected under pressures of from 500 to 10000 bar.

18. The process according to claim 1, characterized in that each ceramic powder layer of the compressed molding includes Er.sub.2O.sub.3.

19. The process according to claim 18, characterized in that the concentration of Er.sub.2O.sub.3 is different in each powder layer, wherein each intermediate layer bounded by two directly neighboring powder layers is surrounded by one neighboring layer that has a higher concentration of Er.sub.2O.sub.3 as compared to the intermediate layer.

20. The process according to claim 19, characterized in that each intermediate layer is surrounded by one neighboring layer that has a lower concentration of Er.sub.2O.sub.3, and one neighboring layer that has a higher concentration of Er.sub.2O.sub.3.

21. The process according to claim 18, characterized in that the compressed molding includes powder layers, in which, proceeding from an outer powder layer, the concentration of Er.sub.2O.sub.3 increases from layer to layer.

22. The process according to claim 18, characterized in that all powder layers include Er.sub.2O.sub.3 in an amount of from 0.01 to 1.5% by weight based on the total weight of the powder layer.

23. The process according to claim 1, characterized in that the base powders have an average grain size D.sub.50 of from 35 μm to 85 μm as measured by laser diffraction.

24. The process according to claim 1, characterized in that the inorganic components of the base powders have an average particle size D.sub.50 of from 0.1 to 1 μm as measured by laser diffraction.

25. The process according to claim 1, characterized in that the concentration of Fe.sub.2O.sub.3 increases from layer to layer, wherein all powder layers include Fe.sub.2O.sub.3 in an amount of from 0.01 to 0.25% by weight based on the total weight of the powder layer.

26. A sintered molding with a color gradient for use in the preparation of dental restorations, obtainable by a process according to claim 1.

27. Use of the molding according to claim 26 for dental restorations, or for preparing dental restorations.

Description

EXAMPLES

[0058] Table 1 shows 4 base powders A to D that are employed for the compositions of the ceramic powder layers. The grain size D.sub.50 of the base powders is within a range of from 40 to 80 μm. The inorganic components of the base powders have a particle size D.sub.50 of from 0.2 to 0.7 μm.

[0059] The indicated weights are respectively based on the total weight of the powder composition.

TABLE-US-00001 TABLE 1 Designation Component Proportion (% by weight) Base powder A Y.sub.2O.sub.3 5.33 Al.sub.2O.sub.3 0.05 organic binder 4 CO.sub.3O.sub.4 0.05 ZrO.sub.2 ad 100 Base powder B Er.sub.2O.sub.3 9.2 Al.sub.2O.sub.3 0.045 organic binder 4 ZrO.sub.2 ad 100 Base powder C Y.sub.2O.sub.3 6.93 Al.sub.2O.sub.3 0.05 organic binder 4 ZrO.sub.2 ad 100 Base powder D Y.sub.2O.sub.3 6.09 Al.sub.2O.sub.3 0.049 organic binder 4 Fe.sub.2O.sub.3 0.2 ZrO.sub.2 ad 100

[0060] The arrangements of the layers set forth in the following Table 2 show the composition of each individual ceramic powder layer in the compressed molding. The compressed moldings are provided for use in the preparation of dental restorations, so that the layer compositions are designed in accordance with the position in the tooth. The compositions of the powder layers are formed from the base powders by varying the proportions to obtain an ideal color gradient. The composition of each powder layer is achieved by homogeneously mixing the base powders in the stated quantities. Subsequently, the powders are placed layer by layer into a cylindrical mold having a diameter of 100 mm, and a layer thickness of 18 mm was set. The powder layers are precompressed uniaxially under a pressure of 13 MPa perpendicular to the layer surface, and subsequently compressed isostatically under a pressure of 2000 bar.

[0061] Subsequently, debinding occurs at about 1000° C. over a period of about 100 hours. The thus obtained white bodies are milled using CAD/CAM systems into dental restorations.

[0062] These presintered and processed white bodies are subsequently subjected to final sintering at 1450° C. over a period of 120 minutes.

TABLE-US-00002 TABLE 2 Base powder Base powder Base powder Base powder Powder Region of C D B A layer restoration (% by weight) (% by weight) (% by weight) (% by weight) 1 Cutting edge 36.90 51.00 6.10 6.00 2 Dentin/Cutting edge 30.30 58.00 6.20 5.50 3 Dentin 17.40 72.00 6.80 3.80 4 Dentin/Neck 10.60 76.00 7.40 6.00 5 Neck 3.70 79.00 8.30 9.00

[0063] In the present Example, the ceramic powder layers are arranged in such a way that layer 1 (cutting edge) comprises 25%, layer 2 (dentin/cutting edge) comprises 15%, layer 3 (dentin) comprises 20%, layer 4 (dentin/neck) comprises 15%, and layer 5 (neck) comprises 25% of the total thickness of the compressed molding.

[0064] FIG. 1 shows examples of dental restorations obtained from the exemplary ceramic molding.

[0065] The layer transitions and color transitions are fluent. The restorations exhibit an excellent edge strength and stability. Reworking and readjusting of the tooth color is not required.

[0066] The optimum structure and compositions of the layers shows a shrinkage during sintering that is substantially homogeneous throughout the layers. This is advantageous, in particular, for a perfectly fitting production of the dental restorations, since laborious reworking can be substantially avoided thereby.

[0067] 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 top side (light layer, cutting edge) and on the bottom side (dark layer, tooth neck) after firing in a kiln. As to the exemplary embodiment, the density of the white bodies and thus the Vickers hardness is always larger on the bottom side than it is on the top side.

[0068] The following Table 3 shows the determined values:

TABLE-US-00003 TABLE 3 Vickers hardness [HV2] according to DIN EN 843 Mean value of Vickers hardness of cutting edge 55.45 Maximum value of Vickers hardness of cutting 59.50 edge Minimum value of Vickers hardness of cutting 51.60 edge Mean value of Vickers hardness of tooth neck 67.76 Maximum value of Vickers hardness of tooth 74.70 neck Minimum value of Vickers hardness of tooth neck 61.20