Phase characterization of lithium silicate biomedical glass-ceramics produced by two-stage crystallization

A commercially available lithium (di)silicate glass-ceramic used for dental prostheses was characterized with respect to its quantitative phase composition and crystallinity. For analysis of quantitative phase content, X-ray diffraction (XRD) was used combined with the G-factor method, an external standard technique. Samples of the material were analyzed in the pre-crystallized state and after final crystallization heat-treatment in order to characterize the changes occurring during the final crystallization stage. The bulk chemical composition of the commercial blocks, matching the composition of the precursor glass, was determined by a combination of X-ray Fluorescence (XRF) and Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES) analysis. In the pre-crystallized sample, Li2SiO3 with low crystallite sizes and clear anisotropic crystallinity was detected as the only crystalline phase. During the second heat-treatment conducted according to the standard routine defined by the manufacturer, Li2Si2O5 and Li3PO4 were formed. A fraction of Li2SiO3 remained, while the size of its crystallites (coherent scattering domains) significantly increased during the second heat-treatment. By combining XRD and XRF/ICP-OES data, the chemical composition of the residual glass phase was determined in the pre- and finally-crystallized samples. The residual glass phases were shown to be enriched in ZrO2, as no Zr4+ containing crystalline phase was detected. Knowledge of the residual glass composition is a step forward in optimizing the mechanical performance of dental glass-ceramics.