Lithium silicate glass ceramic and glass with divalent metal oxide

Abstract

Lithium silicate glass ceramics and glasses containing specific oxides of divalent elements are described which crystallize at low temperatures and are suitable in particular as dental materials.

Claims

1. Lithium silicate glass ceramic which comprises a divalent metal oxide selected from MgO, CaO, SrO, BaO, ZnO and mixtures thereof and comprises at least 12.1 wt.-% Li.sub.2O, wherein the molar ratio between SiO.sub.2 and Li.sub.2O is in the range of from 2.4 to 3.1.

2. Lithium silicate glass ceramic according to claim 1, wherein the molar ratio between SiO.sub.2 and Li.sub.2O is in the range of from 2.4 to 3.0.

3. Glass ceramic according to claim 1, which comprises less than 1.0 wt.-% K.sub.2O.

4. Glass ceramic according to claim 1, which comprises less than 1.0 wt.-% K.sub.2O, Na.sub.2O and mixtures thereof.

5. Glass ceramic according to claim 1, which comprises less than 1.0 wt. % alkali metal oxide other than Li.sub.2O.

6. Glass ceramic according to claim 1, which comprises less than 0.1 wt.-% La.sub.2O.sub.3.

7. Glass ceramic according to claim 1, which comprises the divalent metal oxide or mixtures thereof in an amount of from 0.1 to 15 wt.-%.

8. Lithium silicate glass ceramic which comprises SrO and at least 12.1 wt.-% Li.sub.2O, wherein the molar ratio between SiO.sub.2 and Li.sub.2O is in the range of from 2.2 to 3.1.

9. Lithium silicate glass ceramic according to claim 1, which comprises less than 5.0 wt.-% BaO.

10. Glass ceramic according to claim 1, which comprises 55.0 to 85.0 wt.-% SiO.sub.2.

11. Glass ceramic according to claim 1, which comprises 12.5 to 20.0 wt.-% Li.sub.2O.

12. Glass ceramic according to claim 1, which comprises 0 to 10.0 wt.-% P.sub.2O.sub.5.

13. Glass ceramic according to claim 1, which comprises at least one of the following components: TABLE-US-00003 Component wt.-% SiO.sub.2 67.5 to 79.0 Li.sub.2O 12.5 to 20.0 divalent metal 2.0 to 12.0 oxide or mixtures P.sub.2O.sub.5 0 to7.0 Al.sub.2O.sub.3 0 to 6.0.

14. Glass ceramic according to claim 1, wherein lithium silicate glass ceramic is excluded which comprises at least 6.1 wt.-% ZrO.sub.2.

15. Glass ceramic according to claim 1, wherein lithium silicate glass ceramic is excluded which comprises at least 8.5 wt.-% transition metal oxide selected from the group consisting of oxides of yttrium, oxides of transition metals with an atomic number from 41 to 79 and mixtures of these oxides.

16. Lithium silicate glass ceramic which comprises a divalent metal oxide selected from MgO, CaO, SrO, BaO, ZnO and mixtures thereof and comprises at least 12.1 wt.-% Li.sub.2O, wherein the molar ratio between SiO.sub.2 and Li.sub.2O is in the range of from 2.2 to 3.1 and which comprises lithium metasilicate as a main crystal phase.

17. Glass ceramic according to claim 16, which comprises more than 5 vol.-% lithium metasilicate crystals.

18. Glass ceramic according to claim 16, which comprises more than 10 vol.-% lithium metasilicate crystals.

19. Glass ceramic according to claim 16, which comprises more than 15 vol.-% lithium metasilicate crystals.

20. Glass ceramic according to claim 1, which comprises lithium disilicate as a main crystal phase.

21. Lithium silicate glass ceramic which comprises a divalent metal oxide selected from MgO, CaO, SrO, BaO, ZnO and mixtures thereof and comprises at least 12.1 wt.-% Li.sub.2O, wherein the molar ratio between SiO.sub.2 and Li.sub.2O is in the range of from 2.2 to 3.1 and which comprises more than 10 vol.-% lithium disilicate crystals.

22. Glass ceramic according to claim 21, which comprises more than 20 vol.-% lithium disilicate crystals.

23. Glass ceramic according to claim 21, which comprises more than 30 vol.-% lithium disilicate crystals.

24. Lithium silicate glass ceramic according to claim 1, which has lithium disilicate as a main crystal phase and a fracture toughness, measured as K.sub.IC value, of at least 1.9 MPa.Math.m.sup.0.5.

25. Starting glass, which comprises the components of the glass ceramic according to claim 1.

26. Lithium silicate glass with nuclei which are suitable for forming lithium metasilicate and/or lithium disilicate crystals, wherein the glass comprises the components of the glass ceramic according to claim 1.

27. Glass ceramic according to claim 1, wherein the glass ceramic is present in the form of a powder, a granular material, a blank or a dental restoration.

28. Process for the preparation of the glass ceramic according to claim 1, wherein a starting glass, a glass with nuclei or a glass ceramic with lithium metasilicate as a main crystal phase is subjected to at least one heat treatment in the range of from 450 to 950° C.

29. Process for the preparation of a lithium silicate glass ceramic which comprises a divalent metal oxide selected from MgO, CaO, SrO, BaO, ZnO and mixtures thereof and comprises at least 12.1 wt.-% Li.sub.2O and less than 1.0 wt.-% K.sub.2O, wherein (a) a starting glass is subjected to a heat treatment at a temperature of from 470 to 560° C. for a period of from 10 min to 120 min in order to form the glass with nuclei, and (b) the glass with nuclei is subjected to a heat treatment at a temperature of from 600 to 750° C. in order to form the glass ceramic with lithium disilicate as main crystal phase.

30. Process according to claim 29, wherein the heat treatment in step (b) is carried out for a period of from 10 min to 120 min.

31. A process of using the glass ceramic according to claim 1 as dental material.

32. A process of using a lithium silicate glass ceramic which comprises a divalent metal oxide selected from MgO, CaO, SrO, BaO, ZnO and mixtures thereof and comprises at least 12.1 wt.-% Li.sub.2O, wherein the molar ratio between SiO.sub.2 and Li.sub.2O is in the range of from 2.2 to 3.1, as dental material, wherein the glass ceramic is shaped by pressing or machining to a desired dental restoration.

Description

EXAMPLES

Examples 1 to 17—Composition and Crystal Phases

(1) A total of 17 glasses and glass ceramics according to the invention with the composition given in Table I were prepared by melting corresponding starting glasses followed by heat treatment for controlled nucleation and crystallization.

(2) For this, the starting glasses weighing from 100 to 200 g were first melted from customary raw materials at 1400 to 1500° C., wherein the melting was very easily possible without formation of bubbles or streaks. By pouring the starting glasses into water, glass frits were prepared which were then melted a second time at 1450 to 1550° C. for 1 to 3 h for homogenization.

(3) In the case of Examples 1 to 8 and 10 to 17, the obtained glass melts were then poured into preheated moulds in order to produce glass monoliths. All glass monoliths proved transparent.

(4) In the case of Example 9, the obtained glass melt was cooled to 1400° C. and converted to a finely divided granulate by pouring into water. The granulate was dried and ground to a powder with a particle size of <90 μm. This powder was moistened with some water and pressed to form a powder compact at a pressure of 20 MPa.

(5) The glass monoliths (Examples 1-8 and 10-17) as well as the powder compact (Example 9) were then converted by thermal treatment to glasses and glass ceramics according to the invention. The thermal treatments used for controlled nucleation and controlled crystallization are also given in Table I. The following meanings apply T.sub.N and t.sub.N Temperature and time used for nucleation T.sub.C and t.sub.C Temperature and time used for crystallization of lithium disilicate LS lithium metasilicate LP lithium orthophosphate

(6) It can be seen that a first heat treatment in the range of 470 to 560° C. resulted in the formation of lithium silicate glasses with nuclei and these glasses crystallized by a further heat treatment already at 600 to 750° C. within only 20 to 30 min to glass ceramics with lithium disilicate as main crystal phase, as was established by X-ray diffraction tests.

(7) The produced lithium disilicate glass ceramics had high fracture toughness values, measured as critical stress intensity factor K.sub.IC, of more than 1.9 MPa.Math.m.sup.0.5.

(8) The produced lithium disilicate glass ceramics were able to be very satisfactorily machined in a CAD/CAM process or hot pressed into the form of various dental restorations, which were also provided with a veneer if required.

(9) They were also able to be applied by hot pressing as coatings onto in particular dental restorations, e.g. in order to veneer the latter as desired.

Example 18—Processing Via Powder Compacts

(10) The glass ceramics according to Examples 1, 2, 7 and 12 were ground to powders with an average particle size of <90 μm.

(11) In a first variant, the obtained powder was pressed with or without pressing auxiliaries to powder compacts and the latter were partly or densely sintered at temperatures of 800 to 1100° C. and then further processed by machining or by hot pressing to form dental restorations.

(12) In a second variant, the obtained powders were pressed with or without pressing auxiliaries to powder compacts and the latter were then further processed by machining or by hot pressing to form dental restorations. In particular, the dental restorations obtained after the machining were then densely sintered at temperatures of 900 to 1100° C.

(13) With both variants, it was possible to prepare in particular crowns, caps, partial crowns and inlays as well as coatings on dental ceramics and dental glass ceramics.

Example 19—Hot Pressing of Glass with Nuclei

(14) A glass with the composition according to Example 9 was prepared by mixing corresponding raw materials in the form of oxides and carbonates for 30 min in a Turbula mixer and then melting the mixture at 1450° C. for 120 min in a platinum crucible. The melt was poured into water in order to obtain a finely divided glass granulate. This glass granulate was melted again at 1530° C. for 150 min in order to obtain a glass melt with particularly high homogeneity. The temperature was reduced to 1500° C. for 30 min and cylindrical glass blanks with a diameter of 12.5 mm were then prepared by pouring into pre-heated, separable steel moulds or graphite moulds. The obtained glass cylinders were then nucleated at 560° C. and stress-relieved.

(15) The nucleated glass cylinders were then processed by hot pressing at a pressing temperature of 970° C. and a pressing time of 6 min using an EP600 press furnace, Ivoclar Vivadent AG, to form dental restorations, such as inlays, onlays, veneers, partial crowns, crowns, laminating materials and laminates. In each case, lithium disilicate was detected as main crystal phase.

(16) TABLE-US-00002 TABLE I Example 1 2 3 4 5 6 7 8 Composition wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% SiO.sub.2 73.8 73.8 69.4 68.7 73.8 76.4 73.8 73.8 Li.sub.2O 15.3 15.3 19.7 17.0 15.3 12.7 15.3 15.3 P.sub.2O.sub.5 3.4 3.4 3.4 7.0 3.4 3.4 3.4 3.4 Al.sub.2O.sub.3 3.5 — 3.5 3.4 3.5 3.5 — 3.5 ZrO.sub.2 — 3.5 — — — — — TiO.sub.2 — — — — — — 3.5 — MgO 4.0 4.0 4.0 3.9 — — — — CaO — — — — 4.0 4.0 4.0 — SrO — — — — — — — 4.0 BaO — — — — — — — — ZnO — — — — — — — — CeO.sub.2 — — — — — — — — Tb.sub.4O.sub.7 — — — — — — — — Er.sub.2O.sub.3 — — — — — — — — SiO.sub.2/Li.sub.2O molar ratio 2.4 2.4 1.8 2.0 2.4 3.0 2.4 2.4 Optical properties transparent transparent transparent transparent transparent transparent transparent transparent (after pouring) T.sub.g/° C. 464 475 455 461 468 468 469 466 T.sub.N/° C. 480 500 480 480 490 490 490 490 t.sub.N/min. 10 10 10 10 10 10 10 10 T.sub.C/° C. 700 700 700 700 700 700 700 700 t.sub.C/min. 20 20 20 20 20 20 20 20 Main crystal lithium lithium lithium lithium lithium lithium lithium lithium phase.sub.RT-XRD disilicate disilicate disilicate disilicate disilicate disilicate disilicate disilicate Other crystal phases — LP, LP, — LP — LP, — quartz quartz quartz K.sub.IC/MPa m.sup.1/2 — 1.92 — — 2.41 2.08 Example 9 10 11 12 13 14 15 16 17 Composition wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% SiO.sub.2 75.1 73.8 78.4 75.4 72.9 73.1 72.4 73.3 67.1 Li.sub.2O 15.6 15.3 16.3 15.6 15.1 15.2 15.0 15.2 16.7 P.sub.2O.sub.5 — 3.4 3.3 3.4 3.3 3.4 3.2 3.6 4.8 Al.sub.2O.sub.3 3.6 3.5 — 3.6 5.6 4.2 4.1 3.4 — ZrO.sub.2 — — — — — — 1.5 — — TiO.sub.2 — — — — — 0.5 0.5 — — MgO — — — — — — — — 3.8 CaO — — — 2.0 3.1 — — 4.5 3.8 SrO 4.1 — — — — — — — 3.8 BaO — 4.0 — — — — — — — ZnO — — 2.0 — — 3.6 3.3 — — CeO.sub.2 1.0 — — — — — — — — Tb.sub.4O.sub.7 0.3 — — — — — — — — Er.sub.2O.sub.3 0.3 — — — — — — — — SiO.sub.2/Li.sub.2O 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 molar ratio Optical transparent transparent transparent transparent transparent transparent transparent trans- trans- properties parent parent (after pouring) T.sub.g/° C. 460 469 461 472 468 474 490 466 445 T.sub.N/° C. 560 490 500 500 500 500 500 490 470 t.sub.N/min. 10 10 10 10 10 10 10 10 10 T.sub.C/° C. 750 700 600 650 650 650 720 700 650 t.sub.C/min. 30 20 20 20 20 20 20 20 20 Main crystal Lithium Lithium Lithium Lithium Lithium Lithium Lithium Lithium Lithium phase.sub.RT-XRD disilicate disilicate disilicate disilicate disilicate disilicate disilicate disilicate disilicate Other crystal Lithium LS, — — — — — — LP phases metasilicate, LP, quartz, quartz Li.sub.2O•Al.sub.2O.sub.3•7.5SiO.sub.2 K.sub.IC/MPa .Math. m.sup.1/2 — 2.37 — — — — — — —

(17) Although preferred embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the claims which follow.