Impact of crystallization firing process on the microstructure and flexural strength of zirconia-reinforced lithium silicate glass-ceramics

Objectives. The aim of this study was to characterize the microstructure of two zirconia-reinforced lithium silicate (ZLS) glass-ceramics and evaluate their mechanical properties before and after the crystallization firing process (CFP). Methods. Field emission-scanning electron microscope (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were performed for microstructural characterization. To evaluate the pattern of crystallization and the molecular composition of ZLS glass-ceramics, was used X-ray diffraction (XRD). Vickers hardness, fracture toughness by the indentation method, and biaxial flexural strength were also measured. One hundred and forty ceramic discs were produced (diameter = 12 mm; thickness = 1.2 mm) and allocated among four groups (n = 30): Sfir, Sunf-ZLS Vita Suprinity; and Cfir and Cunf-ZLS Celtra Duo; fired and unfired, respectively. Statistical analysis was performed and Weibull failure probabilities were calculated. Results. Cfir showed the highest characteristic strength (251.25 MPa) and hardness (693.333 +/- 10.85 GPa). Conversely, Sunf presented the lowest characteristic strength (106.95 MPa) and significantly lowest hardness (597.533 +/- 33.97 GPa). According to Weibull analysis, Sunf had the highest structural reliability (m = 7.07), while Sfir presented the lowest (m = 5.38). The CFP was necessary to crystallize zirconia in the partially crystallized ZLS glass-ceramics. Sfir had a lower percentage of crystallized zirconia than did Cfir. Fracto-graphic analyses showed that all failures initiated from an inherent critical defect in Sunf and from processing defects in the remaining groups. Significance. The CFP had a direct influence on the flexural strength and microstructural characteristics of both ZLS materials. (C) 2018 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.