The influence of calcium fluoride (CaF2) on biaxial flexural strength of apatite-mullite glass-ceramic materials

Objective. The aim of this study was to evaluate the effect of varying the molar percentage of calcium fluoride (CaF2) on the biaxial flexural strength (BFS) of apatite-mullite glass-ceramics. Methods. Three apatite-mullite glass-ceramic materials were produced based on a formula of 4.5SiO(2)-3Al(2)O(3)-1.5P(2)O(5)-3CaO-XCaF2, where X=0.5, 1 and 3 and called HG 1-3, respectively. These materials were used to produce discs of 2 mm thickness and 12 mm diameter using the lost-wax casting process. 30 discs per material were produced, 10 discs per material were cast and then left to bench cool (glass state), 10 discs per material were given a heat treatment at 765, 679 and 629 degrees C for I h and then heat treated at 890, 860 and 824 degrees C for the HG 1-3, respectively, for another hour to form apatite. Ten discs per material were heat treated as previously described (765, 679 and 629 degrees C) then heat treated for I h at 1022, 987 and 892 degrees C for the HG 1-32 respectively, to form apatite-mullite. The heat treatment temperatures were obtained from differential thermal analysis data. A lithium disilicate glass-ceramic Was used as a control. Biaxial flexural strength (BFS) was determined using a Lloyd 2000R tester. Results. Data showed that the BFS increased as the fluoride content increased, and the apatite-mullite samples had significantly higher BFS values than the as cast glass or apatite samples (p < 0.05), with the control having significantly higher BFS values than all the HG glass-ceramic materials for every condition (p < 0.05). The fictive glass transition temperature (T.) was observed to drop with increasing fluoride content. Significance. Increasing the CaF2 content increased the BFS and decreased the T. of the glass-ceramic materials tested. (c) 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.