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 sintered molding with a color gradient for use in the preparation of dental restorations, obtained by a process of: a) mixing at least three 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 including at least 4 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 each ceramic powder layer includes a mixture of at least three different base powders in different amounts, at least three of the base powders include 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, 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, each of the ceramic powder layer of the compressed molding includes Er.sub.2O.sub.3, the concentration of Er.sub.2O.sub.3 is different in each of the ceramic powder layer, each intermediate layer which is each powder layer bounded by neighboring layers that are two directly neighboring powder layers, is surrounded by one neighboring layer that has a higher concentration of Er.sub.2O.sub.3 and one neighboring layer that has a lower concentration of Er.sub.2O.sub.3 as compared to the intermediate layer, the compressed molding includes the ceramic powder layers, in which, proceeding from an outer ceramic powder layer, the concentration of Er.sub.2O.sub.3 increases from layer to layer, 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.

2. The sintered molding 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 sintered molding 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 sintered molding according to claim 1, characterized in that at least one of the base powders includes zirconia or zirconia and hafnium oxide in an amount of at least 89% by weight, respectively, based on the total weight of the components of the base powder.

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

6. The sintered molding 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.

7. The sintered molding 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.

8. The sintered molding 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.

9. The sintered molding 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.

10. The sintered molding 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.

11. The sintered molding 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%.

12. The sintered molding according to claim 1, characterized in that the sintered ceramic molding is presintered and processed by subtractive methods before sintering.

13. The sintered molding 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.

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

15. The sintered molding 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.

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

17. The sintered molding according to claim 1, characterized in that the base powders have an average granule size D.sub.50 of from 35 m to 85 m as measured by laser diffraction.

18. The sintered molding according to claim 1, characterized in that the concentration of Fe.sub.2O.sub.3 increases from layer to layer proceeding from an outer powder 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.

19. A dental restoration made from the molding according to claim 1.

Description

(1) 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.

(2) FIG. 1 shows examples of dental restorations obtained from the exemplary ceramic molding.

(3) 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.

(4) 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.

(5) 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.

(6) The following Table 3 shows the determined values:

(7) 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