Crystallization and flexural strength optimization of fine-grained leucite glass-ceramics for dentistry

Objectives: Leucite glass-ceramics with fine-grained leucite crystals promote improved mechanical strength and increased translucency. The objectives of the study were to optimize the microstructure of a fine-grained leucite glass-ceramic in order to increase its flexural strength and reliability as measured by its Weibull modulus. Methods: Glass was prepared by a melt-derived method and ground into a powder (M1A). The glass crystallization kinetics were investigated using high temperature XRD and DSC. A series of two-step heat treatments with different nucleation/crystal growth temperatures and holds were carried out to establish the optimized crystallization heat treatment. Glass-ceramics were characterized using XRD, SEM and dilatometry. The glass-ceramic heat treated at the optimized crystallization parameters (M1A opt) was both sintered (SM1Aopt) and heat extruded (EM1Aopt) into discs and tested using the biaxial flexural strength (BFS) test. Results: High temperature XRD suggested leucite and sanidine crystallization at different temperatures. Optimized crystallization resulted in an even distribution of fine leucite crystals (0.15 (0.09) μm2) in the glassy matrix, with no signs of microcracking. Glass-ceramic M1A opt showed BFS values of [mean (SD), MPa]: SM1Aopt = 252.4 (38.7); and EM1Aopt = 245.0 (24.3). Weibull results were: SM1A opt; m = 8.7 (C.I. = 7.5-10.1) and EM1Aopt; m = 11.9 (C.I. = 9.3-15.1). Both experimental groups had a significantly higher BFS and characteristic strength than the IPS Empress Esthetic glass-ceramic, with a higher m value for the EM1Aopt material (p <0.05). Significance: A processable fine-grained leucite glass-ceramic with high flexural strength and improved reliability was the outcome of this study. © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.