Multi-Layer Structure

Abstract

The present invention relates to a molded body with a color profile for use in the production of dental restorations obtainable by sintering a press-molded body comprising two or more color-different ceramic powder layers, wherein each powder layer comprises at least 80 wt. % of ZrO.sub.2 and is essentially free of iron oxide, characterized in that at least one powder layer comprises terbium oxide (Tb.sub.4O.sub.7).

Claims

1. A sintered molding with a color gradient for use in the preparation of dental restorations, obtainable by sintering a compression molding comprising 2 or more ceramic powder layers having different colors, wherein each powder layer has at least 80% by weight ZrO.sub.2 and is essentially free of iron oxide, characterized in that each powder layer has a different concentration of terbium oxide, erbium oxide, and cobalt oxide.

2. The sintered molding according to claim 1, characterized in that each of the sintered powder layers is subject to an essentially equal volume change over a temperature range of from 25 to 1600 C.

3. The sintered molding according to claim 1, characterized in that the weight ratio of terbium oxide to cobalt oxide is within a range of from 80:1 to 5:1 in at least one powder layer.

4. The sintered molding according to claim 1, characterized in that the blank has layers with different colors, and the sintering process yields a gradual color gradient.

5. The sintered molding according to claim 1, characterized in that at least 2, powder layers have an essentially identical yttria content.

6. The sintered molding according to one or more of claim 1, characterized in that said blank has a translucency gradient.

7. The sintered molding according to claim 1, characterized in that each of the powder layers have at least 0.02% by weight Al.sub.2O.sub.3.

8. The sintered molding according to claim 1, characterized in that at least one of the powder layers include 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 powder layer.

9. The sintered molding according to claim 1, characterized in that the powder layers include 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.

10. The sintered molding according to claim 1, characterized in that the compressed molding consists of 4 or more powder layers.

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 a presintered ceramic molding is processed by subtractive methods.

13. The sintered molding according to claim 1, characterized in that the molding exhibits an increase from layer to layer of the terbium oxide content.

14. The sintered molding according to claim 1, characterized in that the molding contains terbium oxide in an amount of from 0.001 to 0.15% by weight of terbium oxide in each powder layer.

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

16. A process for preparing a sintered molding with a color gradient according to claim 1, comprising the following steps: a) providing 2 or 3 or 4 or 5 or more ceramic powder layers having different colors, which are stacked on one another, b) pressing the layerwise stacked ceramic powder layers to form a compression molding, and c) sintering the molding obtained in step b) to form a ceramic molding, wherein the ceramic powder layers respectively have different compositions, and wherein each powder layer has at least 80% by weight ZrO.sub.2 and is essentially free of iron oxide, characterized in that each powder layer has a different concentration of terbium oxide, erbium oxide, and cobalt oxide.

17. The sintered molding according to claim 2, characterized in that each of the sintered powder layers is subject to an essentially equal volume change over a temperature range of from 900 to 1400 C.

18. The sintered molding according to claim 3, characterized in that the weight ratio of terbium oxide to cobalt oxide is within a range of from 75:1 to 10:1 in at least 2 or 3 powder layers.

19. The sintered molding according to claim 1, characterized in that said blank has an increase of the amount of yttrium oxide from layer to layer.

20. The sintered molding according to claim 1, characterized in that each of the powder layers Al.sub.2O.sub.3 is present in an amount of from 0.03% to 0.15% by weight.

Description

EXAMPLES

[0075] Table 1 shows 5 base powders A to E 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 m. The inorganic components of the base powders have a particle size D.sub.50 of from 0.2 to 0.7 m.

[0076] The indicated weights are respectively based on the total weight of the powder composition.

TABLE-US-00001 TABLE 1 Proportion Designation Component (% by weight) Base powder A Y.sub.2O.sub.3 6.92 Al.sub.2O.sub.3 0.05 Organic binder 4.18 ZrO.sub.2 ad 100 Base powder B Y.sub.2O.sub.3 6.86 Al.sub.2O.sub.3 0.05 Terbium oxide (Tb.sub.4O.sub.7) 0.20 Organic binder 4.26 ZrO.sub.2 ad 100 Base powder C Er.sub.2O.sub.3 11.6 Al.sub.2O.sub.3 0.05 Organic binder 3.78 ZrO.sub.2 ad 100 Base powder D Y.sub.2O.sub.3 6.91 Al.sub.2O.sub.3 0.05 Co.sub.3O.sub.4 0.04 Organic binder 4.25 ZrO.sub.2 ad 100 Base powder E Y.sub.2O.sub.3 9.92 Al.sub.2O.sub.3 0.06 Organic binder 3.7 ZrO.sub.2 ad 100

[0077] 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.

[0078] Subsequently, binder removing 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.

[0079] 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 Base Base Base powder A powder B powder C powder D Powder Region of (% by (% by (% by (% by layer restoration weight) weight) weight) weight) 1 Cutting edge 56.9 28.4 4.2 10.5 2 Dentin/cutting 46.9 36.5 4.7 11.9 edge 3 Dentin 43.9 41.3 5.2 9.6 4 Dentin/neck 36.2 47.2 5.5 11.1 5 Neck 28.8 52.9 5.8 12.5

[0080] 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.

[0081] Surprisingly, it has been found that a sintering distortion could not be observed even at higher temperatures as compared to formulations containing iron oxide that lead to an identical color design. In comparison, a sintering distortion was found in formulations containing iron oxide, known from the prior art. The sintering increases as the iron oxide proportion increases, so that the Vickers hardness in the white body also increases from lighter layers (low proportion of iron oxide) to darker layers (higher proportion of iron oxide). In contrast, the embodiments according to the invention, which are colored with terbium oxide, are free of distortion throughout the layers, and thus the degree of sintering is also homogeneous throughout the layers, which again leads to a homogeneous distribution of the Vickers hardness and thus also to consistent processing properties in CAM processing.

[0082] FIG. 1 shows examples of dental restorations obtained from the exemplary ceramic molding. Front tooth crowns 2 are shown.

[0083] 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.

[0084] 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.

[0085] The following Table 3 shows examples of different VITA classical A1-D4 tooth colors that can be realized with the base powders.

TABLE-US-00003 TABLE 3 Formulation [% by Color Raw material weight] Component [% by weight] A1 Base powder A 84.62 Y.sub.2O.sub.3 6.71459 Base powder B 10.07 Al.sub.2O.sub.3 0.04985 Base powder C 3.00 Tb.sub.4O.sub.7 0.02193 Base powder D 2.31 Co.sub.3O.sub.4 0.00092 Er.sub.2O.sub.3 0.34800 Total: 7.13530 A2 Base powder A 78.10 Y.sub.2O.sub.3 6.57312 Base powder B 14.00 Al.sub.2O.sub.3 0.04975 Base powder C 5.00 Tb.sub.4O.sub.7 0.02972 Base powder D 2.90 Co.sub.3O.sub.4 0.00116 Er.sub.2O.sub.3 0.5800 Total: 7.23375 A3 Base powder A 70.17 Y.sub.2O.sub.3 6.55361 Base powder B 19.44 Al.sub.2O.sub.3 0.04974 Base powder C 5.22 Tb.sub.4O.sub.7 0.04049 Base powder D 5.17 Co.sub.3O.sub.4 0.00207 Er.sub.2O.sub.3 0.60552 Total: 7.25143 A3.5 Base powder A 56.28 Y.sub.2O.sub.3 6.43698 Base powder B 28.80 Al.sub.2O.sub.3 0.04966 Base powder C 6.80 Tb.sub.4O.sub.7 0.05902 Base powder D 8.12 Co.sub.3O.sub.4 0.00325 Er.sub.2O.sub.3 0.78880 Total: 7.33771 A4 Base powder A 49.74 Y.sub.2O.sub.3 6.44178 Base powder B 30.40 Al.sub.2O.sub.3 0.04967 Base powder C 6.70 Tb.sub.4O.sub.7 0.06219 Base powder D 13.16 Co.sub.3O.sub.4 0.00526 Er.sub.2O.sub.3 0.77720 Total: 7.33610

[0086] With respect to the components, the stated weight amounts are supplemented to 100% by weight by the binder and the zirconia.

TABLE-US-00004 TABLE 4 Different tooth colors that can be obtained by mixing base powders. They may serve, for example, as powder layer materials for the sintered moldings according to the invention. GR A3 GR A3 GR A3 GR A3 GR A3 Granules A01 B01 C01 D01 E01 Base powder A [g] 29.969 21.021 42.104 29.787 43.693 Base powder B [g] 5.349 5.160 11.664 10.004 17.416 Base powder C [g] 1.680 1.395 3.132 2.480 4.039 Base powder D [g] 3.002 2.424 3.100 2.729 4.852 Total amount [g] 40.000 30.000 60.000 45.000 70.000

TABLE-US-00005 TABLE 5 Examples of single layer compositions The powder layer compositions are obtained by mixing the base powders. Granules GR A3 A02 GR A3 B02 Base powder E [g] 29.969 21.021 Base powder B [g] 5.349 5.160 Base powder C [g] 1.680 1.395 Base powder D [g] 3.002 2.424 Total amount [g] 40.000 30.000

[0087] The powder compositions for the individual powder layers of the sintered molding according to the invention are obtained by mixing the base powders.

[0088] For preparing the multilayer sintered molding, the layer powder compositions listed in Tables 4 and 5 are compressed in a Weber press (program No. 22; 100 MPa=80 kN). The total charge per block weighed 40 g. The different layers are distributed in the following way as set forth in Tables 6 and 7:

TABLE-US-00006 TABLE 6 Powder composition Layer Height [%] Weighed charge [g] GR A3 A01 A 25 10 GR A3 B01 B 15 6 GR A3 C01 C 20 8 GR A3 D01 D 15 6 GR A3 E01 E 25 10

TABLE-US-00007 TABLE 7 Powder composition Layer Height [%] Weighed charge [g] GR A3 A02 A 25 10 GR A3 B02 B 15 6 GR A3 C01 C 20 8 GR A3 D01 D 15 6 GR A3 E01 E 25 10

[0089] The green body density of the pressed blanks is 3.08 g/cm.sup.3.

[0090] The pressed blanks prepared in Tables 6 and 7 are subsequently freed from binder. The removal of the binder is performed in a Thermo-STAR oven. The removal of the binder or sinter-bonding of the blocks is effected with the following binder removal program (about 20 hours). Tmax=1040 C. (see Table 8).

TABLE-US-00008 TABLE 8 Temperature Heating rate Holding time [ C.] [ C./min] [min] 30 .fwdarw. 280 0.7 280 90 280 .fwdarw. 400 1 400 .fwdarw. 600 10 600 .fwdarw. 1040 5 1040 120 1040 .fwdarw. 30 10

[0091] The white body density of the green bodies with removed binder is 3.17 g/cm.sup.3.

[0092] The Vickers hardness of the white bodies was determined with a Zwick hardness testing machine. Thus, the hardness on the top side and the bottom side was determined each by six measurements and averaging. (testing force 19.61 N; loading level HV 2; waiting time at the load point: 20 s): [0093] Vickers hardness HV 2 (top side): 55.3 [0094] Vickers hardness HV 2 (bottom side): 55.0

[0095] From the white body block, 2 front tooth crowns are milled and subsequently finally sintered, in which the crowns are heated up to 1450 C. at first, then heated at that temperature for 2 hours, and then continuously cooled down to room temperature.

[0096] What is surprising in the sintered bodies according to the invention is the Vickers hardness, in particular. While the Vickers hardness at the presintered blank (white body) increases as the Fe.sub.2O.sub.3 content increases in sintered bodies not according to the invention, the Vickers hardness remains unchanged throughout the block with about 55 HV 2 in sintered bodies according to the invention.

[0097] Under an aesthetic aspect, the variant with the higher yttrium content (Table 8) in the cutting edge offers a somewhat higher translucency along the cutting edge.