Lithium silicate glass ceramic
Lithium silicate materials are described which can be easily processed by machining to dental products without undue wear of the tools and which subsequently can be converted into lithium silicate products showing high strength.
1. Process for the preparation of a lithium silicate glass ceramic wherein lithium disilicate is the main crystalline phase comprising the following components:
Component
wt.- %
SiO 2
64.0-75.0
Li 2 O
13.0-17.0
K 2 O
2.0-5.0
Al 2 O 3
0.5-5.0
Nucleating agent
2.0-5.0
Me(II)O
0-3.0
and which comprises less than 0.1 wt. % of ZnO,
with Me(II)O being selected from at least one of CaO, BaO, MgO and SrO which comprises
(a) producing a starting glass containing the components of the glass ceramic,
(b) subjecting the starting glass to a first heat treatment at a first temperature to give a glass product which contains nuclei suitable for forming lithium metasilicate crystals,
(c) subjecting the glass product to a second heat treatment at a second temperature which is higher than the first temperature to obtain the lithium silicate glass ceramic with lithium metasilicate as the main crystalline phase,
and further subjecting the lithium silicate glass ceramic of step (c) to a third heat treatment at a third temperature of 830 to 880° C. for a period of 10 to 60 minutes.
2. Process according to claim 1 , further comprising forming the lithium disilicate glass ceramic into a dental restoration.
3. Process according to claim 1 , wherein the first heat treatment in step (b) comprises heating the starting glass to a temperature of 500 to 600° C. for a period of about 10 minutes to 3 hours.
4. Process according to claim 1 , wherein the second heat treatment in step (c) comprises heating the glass product to a second temperature of 680° to 720° C.
5. Process according to claim 4 , wherein the second temperature comprises from 690° to 710° C.
6. Process according to claim 5 , wherein the second temperature is about 700° C.
7. Process according to claim 1 , wherein the starting glass of step (a), the glass product of step (b), or the lithium metasilicate glass ceramic of step (c) is shaped to a desired geometry by machining or by hot pressing.
8. Process according to claim 7 , wherein the machining is performed by grinding, trimming or milling.
9. Process according to claim 1 wherein the glass ceramic is essentially free of ZnO.
10. Process according to claim 1 , wherein the glass ceramic comprises 0 to 2.0 wt. % of Me(II)O.
11. Process according to claim 10 , wherein the glass ceramic comprises 0 to 1.5 wt. % of Me(II)O.
12. Process according to claim 1 , wherein Me(II)O is selected from at least one of CaO and MgO.
13. Process according to claim 1 , wherein the glass ceramic comprises 0.1 to 1.0 wt. % of MgO.
14. Process according to claim 13 , wherein the glass ceramic comprises 0.5 to 3.5 wt. % coloring and fluorescent metal oxides.
15. Process according to claim 1 , wherein the molar ratio of SiO 2 :Li 2 O of the glass ceramic is at least 2.2:1.
16. Process according to claim 15 , wherein the glass ceramic comprises a molar ratio of SiO 2 :Li 2 O of at least 2.3:1.
17. Process according to claim 15 , wherein the glass ceramic comprises a molar ratio of SiO 2 :Li 2 O in the range of 2.3:1 to 2.5:1.
18. Process according to claim 1 , wherein the molar ratio of Al 2 O 3 :K 2 O of the glass ceramic is in the range of 1:0.5 to 1:2.0.
19. Process according to claim 18 , wherein the molar ratio of Al 2 O 3 :K 2 O is in the range of 1:1 to 1:2.0.
20. Process according to claim 1 , wherein the glass ceramic comprises 2.5 to 5.0 wt. % of Al 2 O 3 .
21. Process according to claim 1 , wherein the glass ceramic comprises 70.0 to 73.0 wt. % of SiO 2 .
22. Process according to claim 1 , wherein the glass ceramic comprises at least one of the following components in an amount of:
Component
wt. %
Li 2 O
14.0-16.0
K 2 O
3.0-4.5
coloring and fluorescent
0.5-7.5.
metal oxides
23. Process according to claim 1 , wherein the glass ceramic further comprises at least one of the following additional components
Component
wt. %
Na 2 O
0-2.0
B 2 O 3
0-5.0
F
0-5.0.
24. Process according to claim 1 , wherein the nucleating agent is at least one of P 2 O 5 and compounds of the elements Pt, Ag, Cu and W.
25. Process according to claim 1 , further comprising forming the glass ceramic into a blank or a dental restoration.
26. Process according to claim 25 , wherein the dental restoration is an inlay, an onlay, a bridge, an abutment, a facing, a veneer, a facet, a crown, a partial crown, a framework or a coping.
27. Process according to claim 1 , wherein the glass ceramic comprises 64.0 to 73.0 wt. % SiO 2 .
28. Process according to claim 1 , wherein the glass ceramic comprises 1.0 to 4.0 wt. % of ZrO 2 .
29. Process according to claim 1 , wherein the glass ceramic comprises 1.5 to 3.0 wt. % of ZrO 2 .