Lithium silicate glasses or glass ceramics, method for production thereof and use thereof

Abstract

The invention relates to glass ceramics based on the lithium metasilicate system (Li.sub.2O.SiO.sub.2(Li.sub.2SiO.sub.3)), which are mechanically processible in a simple manner in an intermediate stage of the crystallization and, after complete crystallization, represent a high-strength, highly translucent and chemically stable glass ceramic.

Claims

1. A lithium silicate glass ceramic having the following composition: 55 to 64 wt-% SiO.sub.2, 10 to 20 wt-% Li.sub.2O, 8 to 20 wt-% of a stabilizer selected from the group consisting of ZrO.sub.2, HfO.sub.2, and mixtures of ZrO.sub.2 and HfO.sub.2, wherein said stabilizer is not present as a separate crystal phase but is present in an amorphous residual glass phase, 0 to 5 wt-% K.sub.2O, 0.1 to 5 wt-% Al.sub.2O.sub.3, and 0 to 10 wt-% additives.

2. The lithium silicate glass ceramic of claim 1, wherein the stabilizer is a mixture of ZrO.sub.2 and HfO.sub.2.

3. The lithium silicate glass ceramic of claim 1, wherein the additives are selected from the group consisting of nucleating agents, dyes, glass colouring oxides, coloured pigments, and mixtures thereof.

4. The lithium silicate glass ceramic of claim 3, wherein the nucleating agents are selected from the group consisting of phosphorous oxide, titanium oxide, and tin oxide.

5. The lithium silicate glass ceramic of claim 3, wherein the glass colouring oxides are selected from the group consisting of oxides of iron, titanium, cerium, copper, chromium, cobalt, nickel, manganese, selenium, silver, indium, gold, neodymium, praseodymium, samarium, europium, and mixtures thereof.

6. The lithium silicate glass ceramic of claim 3, wherein the additives are selected from the group consisting of boron oxide, fluorine, barium oxide, strontium oxide, magnesium oxide, zinc oxide, calcium oxide, yttrium oxide, titanium oxide, niobium oxide, tantalum oxide, lanthanum oxide, and mixtures thereof.

7. A method for producing a dental restoration comprising a lithium silicate glass ceramic in accordance with claim 1, wherein a) a glass is provided as starting material which comprises the components of the glass ceramic, b) the glass is subjected to a first heat treatment for producing a glass ceramic which comprises lithium metasilicate as exclusive or main crystal phase, and c) the glass ceramic of b) is subjected to a second heat treatment, wherein further metasilicate is segregated from the glass phase and is existent as main crystal phase.

8. The method of claim 7, wherein the first heat treatment is effected with temperatures from 620 C. to 950 C. over a period of 1 to 200 min, and/or the second heat treatment is effected with temperatures from 800 C. to 1040 C. over a period of 5 to 200 min.

9. A shaped dental product comprising a lithium silicate glass ceramic of claim 1.

10. The shaped dental product of claim 9, which is an inlay, an onlay, a bridge, an abutment, a facing, a crown, or a partial crown.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject according to the application is intended to be explained in more detail with reference to the subsequent figures and examples without restricting said subject to these variants.

(2) FIG. 1 is a Scanning Electron microscope (SEM) micrograph of a glass ceramic known from the prior art.

(3) FIG. 2 is a Scanning Electron microscope (SEM) micrograph of a glass ceramic according to the present invention.

(4) FIG. 3 is a Scanning Electron microscope (SEM) micrograph of a glass ceramic with a low content of stabilizer.

DETAILED DESCRIPTION OF THE INVENTION

(5) As can be seen from the figures, the glass ceramic according to the present invention shows much better results resulting in a higher translucency as the prior art glass ceramic of FIG. 1.

(6) The glass ceramic of FIG. 3 has a lower amount of stabilizer (4 wt-%) and shows a number of white spots of the stabilizer (ZrO.sub.2) which results opaque ceramic which is undesirable in the dental field.

Example 1

(7) In Table 1, compositions which are given by way of example are mentioned, from which high zirconium oxide-containing metasilicate glass ceramics can be produced for the dental field.

(8) TABLE-US-00002 TABLE 1 (Data in % by weight) G1 G2 G3 G4 G5 G6 SiO.sub.2 63.5 63.5 59.0 59.0 63.5 63.5 Li.sub.2O 12.9 13.9 18.0 19.0 12.9 12.9 ZrO.sub.2 10.0 9.0 12.0 12.0 12.3 11.0 Al.sub.2O.sub.3 4.7 5.1 4.5 4.5 3.9 4.4 P.sub.2O.sub.5 4.5 4.5 3.5 3.5 3.7 4.2 K.sub.2O 4.4 4.0 3.0 2.0 3.6 4.0

(9) The glasses were melted at 1,500 C. and poured into metal moulds to form blocks. The blocks were stress-relieved in the oven at 560 C. and cooled down slowly. For the various characterisation processes, the glass blocks were divided up and subjected to a first crystallization treatment. For this purpose, the glasses were stored for 10 to 120 minutes at 600 C. to 750 C. As a result of this, glass ceramics with strength values of 150 MPa to 220 MPa (measured according to DIN ISO 6872) were produced. Exclusively lithium metasilicate was hereby established as crystal phase. In this state, processing by means of CAD/CAM methods is possible very readily.

(10) With a second short crystallization at 800 C. to 950 C. for 3 to 15 minutes, the crystallization is continued and the result is an increase in strength from 300 MPa to 450 MPa (measured according to DIN ISO 6872). In addition to the lithium metasilicate phase, a zirconium oxide-containing subsidiary crystal phase can hereby be produced. Also a small conversion of lithium metasilicate into lithium disilicate is possible. The unambiguous main crystal phase remains the lithium metasilicate.

(11) In Table 2, the crystallization conditions of individual glasses and also the resulting crystal phases and strength values are displayed.

(12) TABLE-US-00003 TABLE 2 Glass G1 G2 G3 G4 G5 G6 1. Crystallization 680 C. 700 C. 690 620 C. 680 C. 700 C. 10 min 40 min 120 min 120 min 20 min 20 min 2. Crystallization 820 C. 850 C. 870 C. 880 C. 830 C. 830 C. 15 min 10 min 10 min 8 min 15 min 10 min Crystal phases main phase Metasilicate Metasilicate Metasilicate Metasilicate Metasilicate Metasilicate (>80%) subsidiary ZrO.sub.2- ZrO.sub.2- disilicate disilicate phase (<20%) containing containing Translucence excellent excellent very good very good excellent excellent 3-point bend- 322 MPa 418 MPa 430 MPa 323 MPa 403 MPa 402 MPa ing strength

Example 2

(13) In Table 3, fixed compositions given by way of example for different stabilizer is mentioned, from which high stabilizer-containing metasilicate glass ceramics can be produced for the dental field.

(14) TABLE-US-00004 TABLE 3 in % by weight SiO.sub.2 60.0 Li.sub.2O 19.0 P.sub.2O.sub.5 6.0 Al.sub.2O.sub.3 2.0 K.sub.2O 2.0 CeO.sub.2 1.0 Stabilizer SX* 10.0 *SX represent compositions of the stabilizer S1 to S5 (s. table 4)

(15) Table 4 shows stabilizers used by way of example for dental applications with the composition of table 1.

(16) TABLE-US-00005 TABLE 4 Stabilizers SX S1 Zirconium oxide: 10% S2 Germanium oxide: 10% S3 Lanthanum oxide: 10% S4 Yttrium oxide: 10% S5 Zirconium oxide: 6% Titanium oxide: 4%

(17) The glasses were melted at 1,500 C. and poured into metal moulds to form blocks. The blocks were stress-relieved in the oven at 560 C. and cooled down slowly. For the various characterisation processes, the glass blocks were divided up and subjected to a first crystallization treatment. For this purpose, the glasses were stored for 10 to 120 minutes at 600 C. to 750 C. As a result of this, glass ceramics with strength values of 150 MPa to 220 MPa were produced. Exclusively lithium metasilicate was hereby established as crystal phase. In this state, processing by means of CAD/CAM methods is possible very readily.

(18) With a second short crystallization at 800 C. to 950 C. for 3 to 15 minutes, the crystallization is continued and the result is an increase in strength from 300 MPa to 450 MPa. In addition to the lithium metasilicate phase, a zirconium oxide-containing subsidiary crystal phase can hereby be produced. Also a small conversion of lithium metasilicate into lithium disilicate is possible. The unambiguous main crystal phase remains the lithium metasilicate.

(19) In Table 5, the crystallization conditions of individual glasses and also the resulting crystal phases and strength values are shown for different stabilizers.

(20) TABLE-US-00006 TABLE 5 S1 S2 S3 S4 S5 Crystallization 1 620 C./60 min 540 C./60 min 615 C./60 min 620 C./60 min 620 C./60 min Crystallization 2 850 C./8 min 820 C./8 min 800 C./8 min 820 C./8 min 820 C./8 min Crystal Li-metasilicate, phases (Li-disilicate, Li-phosphate) Trans- excellent very good very good excellent Good lucency 3-point- 418 MPa 341 MPa 325 MPa 363 MPa 358 MPa bending strength