Lithium disilicate glass-ceramic, method for production thereof and use thereof

Abstract

The invention relates to glass-ceramics based on the lithium silicate system which can be mechanically machined easily in an intermediate step of crystallisation and, after complete crystallisation, represent a very strong, highly-translucent and chemically-stable glass-ceramic. Likewise, the invention relates to a method for the production of these glass-ceramics. The glass-ceramics according to the invention are used as dental material.

Claims

1. A lithium silicate glass ceramic that includes at least 10 wt % ZrO.sub.2, from 55 to 70 wt % SiO.sub.2, and from 10 to 15 wt % LiO.sub.2 and having a main crystal phase consisting of lithium disilicate crystal.

2. Lithium silicate glass ceramic of claim 1, which is in the form of a dental restoration.

Description

EXAMPLES 1 TO 6

(1) In examples 1 to 6, compositions of glasses with a high zirconium oxide content are indicated, which are converted by a two-step temperature treatment firstly into readily mechanically machinable lithium metasilicate glass-ceramics and subsequently into highly-translucent, very strong and chemically-stable lithium disilicate glass-ceramics.

(2) The compositions with their components are represented in Table 1.

(3) TABLE-US-00001 TABLE 1 81 82 83 84 85 86 Si0.sub.2 66.9 65.8 65.5 63.7 63.5 63.5 Li.sub.20 13.9 13.7 13.6 13.2 14.4 12.9 Zr0.sub.2 10.0 10.0 12.0 11.7 12.7 13.5 Al.sub.20.sub.3 3.2 3.1 3.1 3.0 3.3 3.5 P.sub.20.sub.5 3.0 3.0 3.0 2.9 3.1 3.4 K.sub.20 2.9 2.9 2.9 2.8 3.0 3.2 Ce0.sub.2 1.0 2.0 Er.sub.20.sub.3 0.2 0.3 Tb.sub.20.sub.3 0.3 0.3

(4) The glasses were melted at 1,500 C. and poured into metal moulds to form blocks. The blocks were stress-relieved at 560 C. in the furnace and cooled slowly. For the different characterisation processes, the glass blocks were divided up and subjected to a first crystallisation treatment. For this purpose, the glasses were aged for 10 to 120 minutes at 600 C. to 750 C. As a result, 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, machining by means of CAD/CAM methods is very readily possible.

(5) With a second short crystallisation at 800 C. to 950 C. for 3 to 15 minutes, recrystallisation of the lithium metasilicate with amorphous SiO.sub.2 from the glass phase takes place to form lithium disilicate and the result is an increase in strength to 300 MPa to 450 MPa. In addition to the lithium disilicate phase, a subsidiary crystal phase with a zirconium oxide content can hereby be produced. In addition, also small residues of lithium metasilicate can be present. The unequivocal main crystal phase is lithium disilicate.

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

(7) TABLE-US-00002 TABLE 2 Glass 81 82 83 84 85 86 1. Crystallisation 650 C. 700 C. 650 C. 700 C. 700 C. 700 C. 20 min 40 min 30 min 20 min 40 min 40 min 2. Crystallisation 850 C. 830 C. 870 C. 850 C. 820 C. 830 C. 10 min 10 min 20 min 8 min 10 min 10 min Crystal phases Main phase disilicate disilicate disilicate disilicate disilicate disilicate (>80%) Subsidiary phase metasilicate metasilicate (<20%) Translucence excellent very good excellent very good excellent excellent 3-point 375 MPa 413 MPa 380 MPa 418 MPa 356 MPa 385 MPa bending strength