Method for producing a shaped body and molding

Abstract

The invention relates to a method for the production of a shaped body comprising at least the method steps of producing a blank having an open porosity by pressing and treating pourable material in a first heat treatment step comprising or consisting of a metal oxide, infiltrating the blank with an infiltration fluid containing a precursor of the metal oxide, precipitating hydroxide of the metal from the infiltration fluid by treating the blank with a basic solution, forming the metal oxide from the hydroxide by treating the blank in a second heat treatment step, wherein the blank is processed before or after the second heat treatment step to achieve a shape that corresponds to the shaped body.

Claims

1. A method for production of a shaped body, comprising the steps of: a) producing a blank having an open porosity through pressing and treatment of a pourable material in a first heat treatment step, the pourable material including a metal dioxide, b) infiltrating the blank with an infiltration fluid, which includes a precursor of the metal dioxide, c) precipitating a hydroxide of the metal dioxide from the infiltration fluid by treatment of the blank with a basic solution, d) forming the metal dioxide from the hydroxide through treatment of the blank in a second heat treatment step, and e) processing the blank before or after the second heat treatment step to achieve a shape corresponding to the shaped body.

2. The method according to claim 1, wherein the second heat treatment step is carried out by sintering of the blank.

3. The method according to claim 1, wherein the metal dioxide embedded in the blank at room temperature after the second heat treatment has a first stabilized crystal phase of at least 50%.

4. The method according to claim 3, wherein the infiltration fluid is such that the metal dioxide formed from the hydroxide has a second crystal phase that differs from the stabilized first crystal phase.

5. The method according to claim 4, wherein the crystals of the second crystal phase have a greater volume than the crystals of the first crystal phase.

6. The method according to claim 1, wherein a tetragonal stabilized zirconium dioxide is used as the metal dioxide of the blank.

7. The method according to claim 1, wherein the pourable material further includes at least one metal oxide powder being selected from the group consisting of Al.sub.2O.sub.3, TiO.sub.2, CeO.sub.2, MgO, Y.sub.2O.sub.3, and a zirconium dioxide mix crystal of the formula:
Zr.sub.1-xMe.sub.xO.sub.2(4n/2)x, wherein Me is a metal which in oxide form is present as a bivalent, trivalent or tetravalent cation (n=2, 3, 4 and 0x1) and stabilizes a tetragonal and/or cubic phase of the zirconium dioxide.

8. The method according to claim 1, wherein the pourable material is one that includes at least one powder containing the metal dioxide as well as at least one organic binder selected from the group consisting of classes of polyvinylalcohols (PVA), polyacrylic acids (PAA), celluloses, polyethyleneglycols, thermoplasts and mixtures thereof.

9. The method according to claim 8, wherein a binder with a percentage in the range 0.1 to 45 vol % is used.

10. The method according to claim 1, wherein the pourable material used is one that includes a zirconium dioxide doped with yttrium oxide (Y.sub.2O.sub.3), calcium oxide (CaO), magnesium oxide (MgO) and/or cerium oxide (CeO.sub.2) and at room temperature the zirconium dioxide is stabilized in the cubic and/or tetragonal crystal form.

11. The method according to claim 1, wherein the infiltration fluid is one in which the metal dioxide formed from the hydroxide after method step d) is monoclinic zirconium dioxide or includes monoclinic zirconium dioxide.

12. The method according to claim 1, wherein a solution or a precursor is used as the infiltration fluid and includes deionized water and an oxychloride of zirconium.

13. The method according to claim 1, wherein the infiltration fluid used for the step of infiltration has a dynamic viscosity of 3.5 MPa.Math.s4.0 MPa.Math.s.

14. The method according to claim 1, wherein the blank is immersed in the infiltration fluid for a period of time t, where t>10 minutes.

15. The method according to claim 1, wherein the blank is penetrated isotropically by the infiltration fluid.

16. The method according to claim 1, wherein for the step of infiltration, the blank is arranged in a negative pressure atmosphere, is then immersed in the infiltration fluid at negative pressure, and is subsequently exposed to atmospheric pressure.

17. The method according to claim 1, wherein after the step of infiltration, the blank is dried with the infiltration fluid.

18. The method according to claim 1, wherein after the step of infiltrating, the blank is dried and then contacted with the basic solution.

19. The method according to claim 18, wherein the basic solution is selected from the group consisting of a 45-55% NH.sub.4OH solution and a 15-25% NaOH solution.

20. The method according to claim 18, wherein during the step of precipitating, the blank is contacted with the basic solution is at room temperature.

21. The method according to claim 18, wherein during the step of precipitating, the blank is contacted with the basic solution for a period of time t where t10 minutes.

22. The method according to claim 18, wherein after the step of infiltration, the blank is dried.

23. The method according to claim 22, wherein after drying of the blank from the precipitating step, the blank is completely sintered, end-sintered or over-sintered.

24. The method according to claim 23, wherein over-sintering is at a temperature that is 5-15% higher than a temperature at which the blank is completely sintered or end-sintered.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 shows a process sequence for a standard sintering program according to the present invention; and

(3) FIG. 2 shows a process sequence for an over-sintering program according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) By means of the teaching according to the invention, a shaped body is provided which has a higher strength compared to those which are not subjected to vacuum infiltration in accordance with the teaching of the invention. This is up to 58% higher.

(5) The strength increase is likely to be due to the sealing of the pores and inhomogeneity (e.g., cracks) in the blank. However, different volumes of the crystal phases as well as the intrinsic stress of the structure are also likely to contribute to the strength increase.

(6) The invention is in particular characterized by a sintered shaped body, in particular in the form of a dental restoration, such as a dental framework, a crown, a partial crown, a bridge, a cap, a veneer, an abutment or a pin construction, wherein the body comprises first particles of zirconium dioxide (ZrO.sub.2), or containing zirconium dioxide, bound through sintering, as a metal oxide and second particles of or containing ZrO.sub.2 present between the first particles. It is characteristic of the shaped body that the shaped body consists of an open-pore matrix formed by the first particles and of pores of the matrix filled by the second particles, the first particles having a predominantly tetragonal phase component, and the second particles having a second crystal phase in part differing from the tetragonal phase and that the shaped body has a bending strength 1000 MPa.

(7) The shaped body according to the invention is characterized by a much higher bending strength, determined according to DIN ISO 6872, compared to those in which the pores are not filled by a metal oxide corresponding to the matrix. The increase in strength is likely to be due not just to the filling of the pores but also to the fact that the metal oxide embedded in the pores has a crystal shape which deviates in terms of volume from the tetragonal crystal form in the matrix and is greater. This is particularly noticeable if the matrix consisting of, or containing, zirconium dioxide, has a tetragonal phase component of more than 80%, preferably more than 90%, in particular more than 95%.

(8) The embedded zirconium dioxide should have a monoclinic phase percentage of at least 50%.

(9) However, there is no departure from the invention even if the zirconium dioxide which is incorporated is likewise doped, i.e., has a substantially tetragonal crystal form; filling the pores with the metal oxide leads to an increase in strength.

(10) According to the invention, a shaped body is provided which consists of, or contains, a first metal oxide forming a matrix into which a metal oxide of the same or different chemical composition is incorporated, which in turn has a crystal shape with a volume which is greater than the volume of the crystal form of the first metal oxide forming the matrix or contained in the matrix.

(11) Further details, advantages and features of the invention result not only from the claims, the features to be derived from theseseparately and/or in combination-, but also from the following description of preferred example embodiments.

(12) To facilitate comparative tests, at 900 C. pre-sintered tetragonal stabilized zirconium dioxide disks each having a thickness of 2 mm and a diameter of 24.8 mm were used.

(13) Each zirconium dioxide (ZrO.sub.2) disk comprises in % by weight: HfO.sub.2<3.0 Al.sub.2O.sub.3<0.3 Technically necessary, unavoidable components0.2 (such as SiO.sub.2, F.sub.2O.sub.3, Na.sub.2O) Y.sub.2O.sub.34.5 to 7.0 Color-imparting oxides:0-1.5
ZrO.sub.2=100(Y.sub.2O.sub.3+Al.sub.2O.sub.3+HfO.sub.2+unavoidable+color-imparting oxides)

(14) Bending strength measurements according to DIN EN ISO 6872 were carried out on these discs or specimens as blanks, after infiltration where necessary, after the specimens have been densely or finely sintered or over-sintered in the following manner.

(15) Some of the samples were previously subjected to a vacuum infiltration process according to the teaching of the invention.

(16) For this purpose a sol or precursor of 70 g ZrOCl.sub.2O.Math.8H.sub.2O per 100 ml solution was prepared as the infiltration fluid, with deionized water used as the solvent.

(17) As a result, a viscosity of the infiltration fluid of 3.89 MPa.Math.s could be achieved, whereby it was insured that the blank was uniformly penetrated by the infiltration fluid and was distributed isotropically after infiltration with the basic solution zirconium dioxide was precipitated.

(18) Some of the pre-sintered porous blanks were then evacuated in a vacuum infiltration system, Cast NVac 1000 (Buehler) for 20 minutes, whereby a pressure of 0.7 bar relative to atmospheric pressure was attained. The blanks were then held in the sol/precursor (infiltration fluid) while maintaining a negative pressure to carry out infiltration. After this immersion, the negative pressure was maintained for a further 5 minutes, with subsequent ventilation by means of a pressure valve. By opening the valve, the infiltration fluid is pressed into the porous specimens. The specimens i.e., blanks were then held in the infiltration fluid at atmospheric pressure for 25 minutes (infiltration time). The infiltration was carried out at room temperature. After removal from the infiltration fluid, the blanks were dried in a heating cabinet at 50 C. for 5 minutes.

(19) Some of the dried samples were then placed in a 51.5% NH.sub.4OH solution (reactant) (corresponds to 25% NH.sub.3 in 100 g solution) and infiltrated at room temperature over a period of 60 minutes.

(20) The infiltrated blanks were then dried again for 5 minutes at 50 C. and finally sintered.

(21) Infiltration with the sol/precursor and subsequent infiltration with the NH.sub.4OH solution leads to the following simplified reaction proceeds (ammonium hydroxide route):
ZrOCl.sub.2+2NH.sub.4OH+H.sub.2O=>Zr(OH).sub.4+2NH.sub.4Cl

(22) Subsequent drying and sintering leads to the formation of zirconium dioxide according to the following reaction equation:
Zr(OH).sub.4=>ZrO.sub.2(solid)+2H.sub.2O(liquid or gas).

(23) Alternatively, some samples, which were previously infiltrated with the infiltration fluid as explained above and then dried, were infiltrated with a twenty percent NaOH solution (reactant) for one hour, also at room temperature. This was followed by drying and sintering. The following reactions proceed through the so-called sodium hydroxide route (again simplified):
ZrOCl.sub.2+2NaOH+H.sub.2O=>Zr(OH).sub.4+2NaCl
and
Zr(OH).sub.4=>ZrO.sub.2(solid)+2H.sub.2O(liquid or gas),
wherein the last reaction is determined through drying and sintering.

(24) The sintering, carried out after infiltration with the basic solution (NaOH or NH.sub.4OH) and drying, generally referred to as end-sintering or complete sintering, was carried out according to the standard sintering program for the blanks, which is shown in FIG. 1.

(25) Some of the samples were over-sintered, i.e., at a temperature approximately 100 C. above that which the manufacturer of the blanks specifies for end-sintering or complete sintering. The process sequence for over-sintering is shown in FIG. 2. It can be seen that the duration of the over-sintering at maximum temperature corresponds to that of complete sintering or end-sintering (FIG. 1).

(26) Biaxial bending tests were then carried out, both for blanks which were not subjected to the vacuum infiltration process (reference samples), as well as blanks infiltrated by the sodium hydroxide route and ammonium hydroxide route. The measurements were carried out in accordance with DIN EN ISO 6872 (Dentistry Ceramic Materials). For determination of the biaxial bending strength, the samples were placed on three hardened steel spheres. These were arranged in a circle with a radius of 6 mm (radius of support circle). The fourth contact point was created by the force-transferring fracture tool (radius of the upper stamp: 0.70 mm). A bending test machine Z020 and the associated software TestXpert II (Zwick GmbH and Co. KG, Germany) were used. The initial force was 2 N and the velocity of the initial force 5 mm/minute. The test speed of 1 mm/minute corresponded to that given in DIN EN ISO 6872.

(27) The biaxial bending tests were carried out on 30 samples which were infiltrated by the ammonium hydroxide route and on 30 reference samples, i.e., blanks, which were not infiltrated.

(28) The mean bending strength value of the reference samples sintered with the standard sintering program (FIG. 1) was 736 MPa, with a standard deviation of 95.9 MPa, a Weibull modulus of 9.2 and a Weibull strength of 777 MPa. The mean bending strength value of the samples of the ammonium hydroxide route was 1087 MPa, with a standard deviation of 119.6 MPa, a Weibull modulus of 10.9 and a Weibull strength of 1137 MPa.

(29) The biaxial bending test of the reference samples sintered with the sintering program over-sintering (FIG. 2) yielded a mean bending strength value of 878 MPa, a standard deviation of 95.8 MPa, a Weibull modulus of 11.1 and a Weibull strength of 918 MPa. The mean bending strength of the over-sintered samples of the ammonium hydroxide route was 1144 MPa, with a standard deviation of 263.8 MPa, a Weibull modulus of 4.5 and a Weibull strength of 1258 MPa.

(30) The tests of blanks infiltrated by the sodium hydroxide route yielded strength values corresponding to those of the ammonium hydroxide route.

(31) A comparison of the numerical values shows that with the standard sintering program, the mean bending strength value was 48% higher than that of the reference samples when the ammonium hydroxide route was selected. The Weibull strength was increased by 46%.

(32) In order to produce a shaped body, in particular a dental shaped body, such as a dental restoration, in particular a dental framework, crown, partial crown, cap, veneer, abutment or pin construction, the blank is in principle machined before the end-sintering or over-sintering process, in particular by milling. In this case, the shrinkage resulting from the complete sintering or end-sintering/over-sintering must be taken into account. Alternatively, machining can also be carried out after the sintering process.