title: Crystallization and flexural strength optimization of fine-grained leucite glass-ceramics for dentistry.
abstract: OBJECTIVE
  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 (SM1A(opt)) and heat extruded (EM1A(opt)) 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) μm(2)) in the glassy matrix, with no signs of microcracking. Glass-ceramic M1A(opt) showed BFS values of [mean (SD), MPa]: SM1A(opt)=252.4 (38.7); and EM1A(opt)=245.0 (24.3). Weibull results were: SM1A(opt); m=8.7 (C.I.=7.5-10.1) and EM1A(opt); 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 EM1A(opt) material (p<0.05).
  
  
  CONCLUSIONS
  A processable fine-grained leucite glass-ceramic with high flexural strength and improved reliability was the outcome of this study.
authors.affiliation: Centre of Adult Oral Health, Queen Mary University of London, Barts and The London School of Medicine and Dentistry, Institute of Dentistry, Turner Street, London, E12AD, UK.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Chen
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Chadwick
authors.forename: Rory M
authors.initials: RM
authors.lastname: Wilson
authors.forename: Robert G
authors.initials: RG
authors.lastname: Hill
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Cattell
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002516:Ceramics / Q000138:chemical synthesis / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D006358:Hot Temperature; D008422:Materials Testing; D018583:Pliability; D012031:Refractometry; D016019:Survival Analysis
chemical_list: D000538:Aluminum Silicates; D003776:Dental Porcelain; C078519:leucite; C023506:Glass ceramics