Zirconia-based monophase and multiphase materials

Abstract

Zirconium oxide material and a sintered molded body produced from the material. The zirconium oxide is present in the tetragonal phase in an amount of 70 to 99.9 vol.-%. The tetragonal phase is chemically stabilized with rare-earth oxides. The sintered moldings can be used, e.g., in the medical field as implants or as dental prostheses.

Claims

1. A zirconia material comprising: zirconia; and a chemical stabilizer; wherein 70 to 100 vol % of the zirconia is present in a tetragonal phase, and wherein the chemical stabilizer comprises at least one oxide of a rare earth metal and wherein the chemical stabilizer chemically stabilizes the tetragonal phase; wherein the content of zirconia is between 94 and 96 vol %; and wherein the zirconia material comprises a second main component is present with a volume amount between 4 and 6 vol %, wherein the second main component consists of a relative amount of more than 80 vol % strontium aluminate or lanthanum aluminate, and wherein the chemical stabilizer is selected from the group consisting of Sm.sub.2O.sub.3 and Gd.sub.2O.sub.3.

2. The zirconia material according to claim 1, wherein the chemical stabilizer is Sm.sub.2O.sub.3 .

3. The zirconia material according to claim 1, wherein 94 to 99.9% of the zirconia is present in the tetragonal phase.

4. The zirconia material according to claim 1, wherein 98 to 99.9% of the zirconia is present in the tetragonal phase.

5. The zirconia material according to claim 2, wherein the Sm.sub.2O.sub.3 is present in an amount between 1 and 5 mol % relative to the zirconia content.

6. The zirconia material according to claim 1, wherein the chemical stabilizer is Gd.sub.2O.sub.3 and is present in an amount between 1 and 5 mol % relative to the zirconia content.

7. The zirconia material according claim 1, wherein the chemical stabilizer content is <15 mol %.

8. The zirconia material according to claim 1, wherein the zirconia comprises a soluble constituent.

9. The zirconia material according to claim 1, wherein the zirconia comprises a soluble constituent comprising a member selected from the group consisting of a Cr compound, a Fe compound, a Mg compound, a Ca compound, a Ti compound, an Y compound, a Sc compound, a lanthanoid compound and a V compound.

10. The zirconia material according to claim 1, wherein the second main component consists of strontium aluminate.

11. The zirconia material according to claim 1, wherein the zirconia material has a hardness of less than 1250 (HV10).

12. The zirconia material according to claim 1, wherein the zirconia material has a breaking strength of ?500 MPa.

13. The zirconia material according to claim 1, wherein the zirconia material has a breaking strength of ?800 MPa.

14. The zirconia material according to claim 1, wherein the damage tolerance and/or residual strength after HV50 indentation is >400 MPa.

15. The zirconia material according to claim 1, wherein the zirconia material has an improved hydrothermal aging resistance, wherein the amount of monoclinic zirconia in the total zirconia content amounts to less than 17 vol % after storage in a hydrothermal atmosphere in an autoclave at 134? C. and 2.2 bar pressure and a cycle of 10 hours.

16. A sintered molding comprising the zirconia material according to claim 1 that has been molded and then sintered to form a sintered molded product, wherein the sintered molding is densely sintered or partially sintered, and wherein the sintered molded product can be mechanically processed without being damaged.

17. An artificial dental prosthesis, spinal implant or medical instrument comprising the sintered molding of claim 16.

18. A dental restoration comprising the zirconia material of claim 1, wherein the dental restoration is selected from the group consisting of a bridge, a crown, an inlay, an onlay, a tooth root pin, an implants and an abutment.

19. The zirconia material according to claim 1, wherein the chemical stabilizer is Gd.sub.2O.sub.3.

Description

(1) These findings are explained in greater detail below on the basis of figures and experimental series without restricting them:

(2) The figures show:

(3) FIG. 1: Diagram showing the hardness of sintered moldings made of zirconia as a function of the chemical stabilizer used.

(4) FIG. 2: Diagram showing the fracture toughness of sintered moldings made of zirconia as a function of the chemical stabilizer used.

(5) FIG. 3: Structural grain size as a function of the chemical stabilizer used.

(6) FIG. 4: Structure-forming agent as a function of the chemical stabilizer used.

(7) FIG. 5: Residual strength values after HV50 damage as a function of the chemical stabilizer used.

(8) FIG. 6: Damage tolerance characteristic lines of zirconia materials according to the invention, composite material according to the invention and reference Y-TZP.

(9) FIG. 7: Hydrothermal aging resistance as a function of the chemical stabilizer used.

EXPERIMENTAL SERIES 1

Hardness as a Function of the Chemical Stabilizer (FIG. 1)

(10) FIG. 1 shows the results of an experimental series with chemical stabilizers according to the invention. The chemical stabilizers yttria (Y.sub.2O.sub.3), cerium oxide (CeO.sub.2), samarium oxide (Sm.sub.2O.sub.3) and gadolinium oxide (Gd.sub.2O.sub.3) were tested along with a composite material according to the invention of strontium hexa-aluminate-reinforced zirconia (strontium hexa-aluminate-toughened zirconia). It has surprisingly been found that the variant with Ce stabilization has much lower hardness values in comparison with the Y stabilization. Samarium oxide and gadolinium oxide produce only a minor reduction in hardness, but this reduction is significant in the case of samarium oxide. The hardness was determined by means of a Vickers hardness test (HV10) with a force of 98.07 N.

(11) With regard to the use according to the invention in the dental field, lower hardness values are desired. In the molar dental field, an artificial dental prosthesis made of Y-TZP, which is frequently used, may come in hard contact with a natural tooth. The hardness of Y-TZP is approximately 1250 (HV10). The natural tooth and/or the enamel has a definitely lower hardness of approximately 400 (HV10) because of the incorporated hydroxylapatite crystals. This difference in hardness can result in substantial abrasion of the natural tooth in a case of stress-related tooth grinding movement (bruxism). In addition, a lower hardness of the zirconia material facilitates damage-free hard processing. Therefore, another preferred embodiment of the invention comprises a zirconia material containing stabilizers which reduce the hardness of the zirconia material wherein the hardness of a sintered body produced from the zirconia material is less than 1250 (HV10), preferably less than 900 (HV10).

EXPERIMENTAL SERIES 2

Fracture Toughness as a Function of the Chemical Stabilizer (FIG. 2)

(12) FIG. 2 shows an experimental series which represents the influence of the chemical stabilizer on the fracture toughness of the zirconia material. It has surprisingly been found that the use of cerium oxide (CeO.sub.2), samarium oxide (Sm.sub.2O.sub.3) and gadolinium oxide (Gd.sub.2O.sub.3) as chemical stabilizers definitely increases the fracture toughness. The fracture toughness of the variants according to the invention was determined on the Vickers hardness indentation (HV10). The variants according to the invention with CeO.sub.2 stabilization did not have any cracks at the hardness indentation. The variants according to the invention with Sm.sub.2O.sub.3 and Gd.sub.2O.sub.3 stabilization had few or no cracks at the hardness indentation. The variants which did not have any cracks at the hardness indentation are extremely tough zirconia materials. Their fracture toughness was estimated by extrapolation to 15 MPa*m^0.5. The range of extrapolated values is shown in FIG. 2 above a dotted line and relates to values above 13.4 MPa*m^0.5. This value is the highest measured fracture toughness that was measured with this determination method.

EXPERIMENTAL SERIES 3

Structural Grain Size and Structure-forming Agents as a Function of the Chemical Stabilizer (FIGS. 3 and 4)

(13) FIGS. 3 and 4 show the influence of the chemical stabilizer on the structural grain size of the zirconia material according to the invention. The structure was evaluated using a scanning electron microscope. The grain size was determined according to the line cut method for determining the mean cut length grain size of a structural phase. It has surprisingly been found that, by using gadolinium oxide and samarium oxide, the structure of the material can be refined. Use of samarium oxide led to an average structural grain size of 0.16 ?m. Use of gadolinium oxide led to an average structural grain size of 0.24 ?m. The zirconia variant according to the invention with Gd.sub.2O.sub.3 stabilization shows local formation of coarse grains in the structural pattern (see FIG. 4). The individual coarse grains are present in the cubic zirconia phase, which slightly promotes the translucency of the material according to the invention in comparison with that of the dental standard Y-TZP.

EXPERIMENTAL SERIES 4

Damage Tolerance as a Function of Chemical Stabilizers (FIG. 5)

(14) FIG. 5 shows zirconia materials according to the invention with different stabilizers. The x axis shows the various materials on the basis of the stabilizers used. The residual strength of the materials according to the invention after HV50 damage has been plotted in MPa on the Y axis.

(15) It is clearly apparent that in the case of the zirconia materials according to the invention and composite materials, the residual strength values increase by a multiple in comparison with the reference material and/or the Y-TZP dental standard.

EXPERIMENTAL SERIES 5

Damage Tolerance Characteristic Lines of the Zirconia Material According to the Invention and Composite Material in Comparison with State-of-the-art Materials (FIG. 6)

(16) FIG. 6 shows the residual strength values after different damages (here: Vickers hardness indentations with different loads of 3 to 500 N) of different material systems, a ZTA (zirconia-toughened alumina), a Y-TZP (Y-stabilized polycrystalline zirconia), a zirconia material Sm-TZP according to the invention and a composite material according to the invention (strontium hexa-aluminate-toughened zirconia). The tested indentation load has been plotted logarithmically in Newtons on the x axis as a function of the residual moisture in MPa on the y axis.

(17) In comparison with materials from the prior art, it is found that the novel materials according to the invention have significantly higher damage tolerance after different damage loads with a uniform initial strength.

EXPERIMENTAL SERIES 6

Hydrothermal Aging Resistance as a Function of the Chemical Stabilizer (FIG. 7)

(18) FIG. 7 shows the hydrothermal aging resistance of the zirconia materials according to the invention as a function of the stabilizer used. To do so, the monoclinic phase component before and after aging was measured on polished sintered moldings by means of X-ray diffractometry.

(19) The moldings were stored in hydrothermal atmosphere in an autoclave at 134? C. and 2.2 bar pressure, running through a cycle of 10 hours.

(20) It has surprisingly been found that the variant according to the invention with CeO.sub.2 stabilization does not exhibit any hydrothermal aging. The variants according to the invention with Sm.sub.2O.sub.3 and Gd.sub.2O.sub.3 stabilization show a slight but significant improvement in the hydrothermal stability in comparison with the reference material Y-TZP.

(21) Thus the zirconia material according to a particularly preferred embodiment of the invention has an improved hydrothermal aging resistance. The improved aging resistance is manifested in the fact that the amount of monoclinic zirconia in the total zirconia content amounts to less than 17 vol % and preferably less than 10 vol % and especially preferably less than 5 vol % after storage in a hydrothermal atmosphere in an autoclave at 134? C. and 2.2 bar pressure with a cycle of 10 hours.

(22) The advantages of the zirconia material according to the invention are summarized again in the following section: the zirconia material according to the invention and sintered moldings according to the invention are produced by means of the known conventional ceramic technology 3-step sintering (prefiring, HIP, white firing) is possible, resulting in a greater strength no hydrothermal aging due to the use of CeO.sub.2 as a chemical stabilization damage-free hard processing, in particular mechanical hard processing of densely sintered or partially sintered intermediate products is possible easier hard processing due to lower material hardness (equivalent to less tool wear) lower hardness therefore definitely reduced abrasion of the natural antagonist in the molar area, among other things use as a fully anatomical system is possible, i.e., veneers are not needed in the molar area, therefore additional cost savings for the patient and reduction in the risk of chipping of parts of the veneer (chip off) aesthetics suitable for dental standards compensation for lack of resilience (damping and/or elasticity of the tooth in chewing action) in the case of a complete dental restoration with implant, i.e., definitely reduced buildup of stress with a chewing action zirconia material can be used to produce blanks and/or blocks for CAD/CAM processing in the presintered or densely sintered condition use of the sintered moldings as dental prostheses, for example, restorations (bridges, crowns, inlays, onlays), as dental root pins, implants, abutments use to produce spinal cages, medical instruments, etc.