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US-12623954-B2 - Lithium silicate glass ceramic with easy machinability

US12623954B2US 12623954 B2US12623954 B2US 12623954B2US-12623954-B2

Abstract

A lithium silicate glass ceramic having lithium metasilicate as main crystal phase and having not more than 30 wt.-% of lithium metasilicate crystals.

Inventors

  • Christian Ritzberger

Assignees

  • IVOCLAR VIVADENT AG

Dates

Publication Date
20260512
Application Date
20220819
Priority Date
20210823

Claims (19)

  1. 1 . A lithium silicate glass ceramic, which comprises lithium metasilicate as main crystal phase and comprises not more than 30 wt.-% of lithium metasilicate crystals, wherein the glass ceramic comprises 0.5 to 7.0 wt.-% P 2 O 5 and wherein the molar ratio of SiO 2 to Li 2 O is in the range of 2.9 to 5.0.
  2. 2 . The glass ceramic according to claim 1 , which comprises not more than 28 wt. % of lithium metasilicate crystals.
  3. 3 . A lithium silicate glass ceramic, which comprises lithium metasilicate as main crystal phase and comprises not more than 30 wt.-% of lithium metasilicate crystals, wherein the molar ratio of SiO 2 to Li 2 O is in the range of 2.9 to 5.0 and wherein the average size of the lithium metasilicate crystals is in the range of 5 to 80 nm.
  4. 4 . The glass ceramic according to claim 1 , which comprises 71.0 to 82.0 wt.-% SiO 2 .
  5. 5 . The glass ceramic according to claim 1 , which comprises 6.0 to 14.0 wt.-% Li 2 O.
  6. 6 . The glass ceramic according to claim 1 , which comprises 4.0 to 13.0 wt.-% further oxide of monovalent elements Me I 2 O, wherein Me I 2 O is selected from Na 2 O, K 2 O, Rb 2 O, Cs 2 O and mixtures thereof.
  7. 7 . The glass ceramic according to claim 1 , which comprises 2.0 to 10.0 wt.-% Al 2 O 3 .
  8. 8 . The glass ceramic according to claim 1 , which comprises 1.0 to 4.0 wt.-% P 2 O 5 .
  9. 9 . The glass ceramic according to claim 1 , which comprises at least one of the following components in the amounts indicated: Component Wt.-% SiO 2 73.1 to 80.0 Li 2 O 7.0 to 12.9 Me I 2 O 4.0 to 15.0 Al 2 O 3 4.0 to 10.0 P 2 O 5 1.2 to 2.6 Me II O 0 to 9.0 Me III 2 O 3 0 to 8.0 Me IV O 2 0 to 10.0 Me V 2 O 5 0 to 8.0 Me VI O 3 0 to 5.0 Fluorine 0 to 1.0, wherein Me I 2 O is selected from Na 2 O, K 2 O, Rb 2 O, Cs 2 O and mixtures thereof, Me II O is selected from MgO, Cao, SrO, ZnO and mixtures thereof, Me III 2 O 3 is selected from B 2 O 3 , Y 2 O 3 , La 2 O 3 , Ga 2 O 3 , In 2 O 3 and mixtures thereof, Me IV O 2 is selected from TiO 2 , ZrO 2 , GeO 2 , SnO 2 , CeO 2 and mixtures thereof, Me V 2 O 5 is selected from V 2 O 5 , Nb 2 O 5 , Ta 2 O 5 and mixtures thereof; and Me VI O 3 is selected from MoO 3 , WO 3 and mixtures thereof.
  10. 10 . The glass ceramic according to claim 1 , wherein the molar ratio of SiO 2 to Li 2 O is in the range of 3.3 to 5.0.
  11. 11 . The glass ceramic according to claim 1 , wherein the glass ceramic is in a form of a powder, a granulate, a blank or a dental restoration.
  12. 12 . A process for the preparation of the glass ceramic according to claim 1 , wherein a starting glass is subjected to at least one heat treatment in the range of 450 to 750° C.
  13. 13 . The process according to claim 12 , in which (a) the starting glass is subjected to a heat treatment at a temperature of 450 to 600° C. to form starting glass with nuclei, and (b) the starting glass with nuclei is subjected to a heat treatment at a temperature of 550 to 750° C. to form the glass ceramic.
  14. 14 . A process of using the glass ceramic according to claim 1 , for coating a dental restoration or for preparation of a dental restoration.
  15. 15 . The process according to claim 14 , wherein the glass ceramic is given the shape of the dental restoration comprising a bridge, inlay, onlay, veneer, abutment, partial crown, crown or facet, by pressing or machining.
  16. 16 . The process according to claim 14 , wherein the glass ceramic is subjected to a heat treatment at a temperature of 750 to 950° C. for a duration of 1 to 60 minutes.
  17. 17 . The process according to claim 14 , in which the preparation of the dental restoration is performed by machining using a CAD/CAM process.
  18. 18 . A lithium silicate glass ceramic, which comprises lithium metasilicate as main crystal phase and comprises not more than 30 wt.-% of lithium metasilicate crystals, wherein the glass ceramic comprises 5.1 to 10.0 wt.-% K 2 O and wherein the molar ratio of SiO 2 to Li 2 O is in the range of 2.9 to 5.0.
  19. 19 . The glass ceramic according to claim 18 , wherein the glass ceramic comprises 5.5 to 10.0 wt.-% K 2 O.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to European patent application No. 21192545.8 filed on Aug. 23, 2021, which disclosure is incorporated herein by reference in its entirety. TECHNICAL FIELD The invention relates to lithium silicate glass ceramic, which is particularly suitable for use in dentistry and in particular for the preparation of dental restorations, and to precursors for the preparation of this glass ceramic. BACKGROUND Lithium silicate glass ceramics are generally characterized by very good mechanical properties, which is why they have been used for some time in the dental field, primarily for the fabrication of dental crowns and small dental bridges. WO 95/32678 A2 and corresponding U.S. Pat. No. 6,376,397, which U.S. patent is hereby incorporated by reference in its entirety, describe lithium disilicate glass ceramics which are processed into dental restorations by pressing in a viscous state. However, the use of a deformable crucible is mandatory, which makes the processing very complex. EP 0 827 941 A1 and EP 0 916 625 A1 disclose lithium disilicate glass ceramics which can be given the shape of the desired dental restoration by pressing or machining. EP 1 505 041 A1 and corresponding U.S. Pat. No. 7,316,740, which U.S. patent is hereby incorporated by reference in its entirety, and EP 1 688 398 A1 describe processes for producing dental restorations of lithium disilicate glass ceramics. In this process, a glass ceramic with lithium metasilicate as the main crystal phase is first produced as a precursor, which can be machined, e.g. by means of a CAD/CAM process. This precursor is then subjected to further heat treatment to form the desired high-strength lithium disilicate glass ceramic. The machining of conventional lithium disilicate glass ceramics is difficult due to their high strength and is therefore regularly associated with high wear of the tools used. The machining of lithium metasilicate glass ceramics is basically easier and possible with less tool wear. However, the known lithium metasilicate glass ceramics can only be machined relatively slowly, for example by the grinding tools of common CAD/CAM machines. This is particularly problematic for the frequently desired provision of a patient with a dental restoration in a single treatment session (so-called chairside treatment). SUMMARY Therefore, there is a need for lithium silicate glass ceramics, which can be machined faster than the known lithium metasilicate glass ceramics and can subsequently be converted into high-strength dental products which also exhibit high chemical resistance and excellent optical properties. This problem is solved by the lithium silicate glass ceramic according to the claims. Subject of the invention are also the starting glass according to the claims and a process according to the claims. DETAILED DESCRIPTION The lithium silicate glass ceramic according to the invention is characterized in that it has lithium metasilicate as main crystal phase and comprises no more than 30 wt.-% of lithium metasilicate crystals. Surprisingly, it has been shown that the glass ceramic according to the invention incorporates a combination of very desirable mechanical and optical properties, as required especially for a dental restoration material. This glass ceramic has a low strength and toughness and accordingly can be easily and in a very short time machined into the shape of even complicated dental restorations, but after such machining can be converted by heat treatment into a glass ceramic product having excellent mechanical properties, excellent optical properties and very good chemical stability. The team “main crystal phase” is used to describe the crystal phase which has the highest proportion by mass of all the crystal phases present in the glass ceramic. The masses of the crystal phases are determined in particular using the Rietveld method. A suitable procedure for the quantitative analysis of the crystal phases by means of the Rietveld method is described, for example, in the dissertation by M. Dittmer “Glasses And Glass-Ceramics In The System MgO—Al2O3—SiO2 With ZrO2 As Nucleating Agent,” University of Jena 2011. Preferably, the glass ceramic according to the invention comprises no more than 28 wt.-%, preferably no more than 26 wt.-% and particularly preferably no more than 22 wt.-% of lithium metasilicate crystals. Particularly preferably, the glass ceramic comprises 10 to 30 wt.-%, preferably 12 to 28 wt.-%, more preferably 15 to 26 wt.-% and most preferably 18 to 22 wt.-% of lithium metasilicate crystals. It is further preferred that in the glass ceramic according to the invention the average size of the lithium metasilicate crystals is in the range of 5 to 80 nm, in particular in the range of 10 to 50 nm, preferably in the range of 15 to 45 nm and particularly preferably in the range of 25 to 35 nm. The average size of the lithium metasilicate crystals can be determi