Concurrent kinetics of crystallization and toughening in multicomponent biomedical SiO2-Li2O-P2O5-ZrO2 glass-ceramics

We investigate here the crystallization kinetics of two pre-crystallized multicomponent dental glass-ceramics (IPS e.max® CAD, Ivoclar-Vivadent; Suprinity® PC, Vita Zahnfabrik) by interrupting the heat treatment at different periods of the non-isothermal and isothermal stage at 840°C. Differential scanning calorimetry (DSC) was used to characterize the crystallization peaks of the pre-crystallized and the base glass, and dilatometry was used to determine the coefficient of thermal expansion and Tg after different times at the maximum temperature. The evolution of crystallinity was tracked by XRD, while the evolution of fracture toughness was obtained by the ball-on-three-balls surface crack in flexure method. The change in microstructural features was made visible using FE-SEM. We show that the isothermal stage is dominated by the transformation of Li2SiO3 in Li2Si2O5, inducing the impingement of nanocrystals into clusters. The residual glass became thereby less polymerized. The kinetics of toughening followed closely the evolution of crystallinity in both systems.