THE EFFECT OF MICROSTRUCTURAL FEATURES ON THE BIAXIAL FLEXURAL STRENGTH OF LEUCITE REINFORCED GLASS-CERAMICS

In this study the effect of size and distribution of leucite crystals on the biaxial flexural strength of five leucite reinforced glass-cera mics used in dentistry for the construction of veneers was investigate d. Three of these were found to have a non-uniform distribution of leu cite crystals, which were associated with a considerable degree of mic rocracking in the glassy matrix around the leucite crystals. The mean values of biaxial flexural strength of these ceramics ranged from 56 t o 70 MPa. The other two ceramics exhibited a more uniform distribution in their leucite crystals, which were also finer in size. The latter ceramics had a significantly higher biaxial flexural strength which ra nged from 120 to 137 M Pa. When the particle size of the starting powd ers of the three low strength ceramics was reduced, a more uniform mic rostructure with less evidence of microcracking was produced in the fi red ceramics and the biaxial flexural strength values were significant ly increased. We conclude that uniformity of microstructure and leucit e crystal size are major factors in determining the biaxial flexural s trength of leucite reinforced glass-ceramics.