Effect of P2O5 on Crystallization Behavior and Chemical Resistance of Dental Glasses in the Li2O-SiO2-ZrO2 System

Commercial dental lithium disilicate based glass-ceramics containing various amounts of P2O5 were synthesized. Regarding the crystallization behavior and physico-chemical properties of the glasses, the optimum percent of P2O5 was determined.as 8 %wt. Crystallization behavior of the glasses was investigated by X-ray diffraction (XRD) and differential thermal analysis (DTA). The micro-hardness and chemical resistance of both glass and glass-ceramic searies were also determined. According to our results, lithium phosphate was precipitated prior to crystallization of the main phases, i.e lithium meta silicate and lithium disilicate. This early precipitation led to evacuation of residual glass phase from lithium ions, which caused increasing the viscosity of glass and so shifting of crystallization to higher temperatures. In addition, increasing in P2O5 amounts and consequently increasing in Li3PO4, led to significant decrease in the crystallite size and aspect ratio  of crystals. Furthermore, while the chemical resistance of the glasses was decreased with P2O5, it was increased with P2O5 after heat treatment process. The chemical solubility of these three glass-ceramics was between 2080~1188 μg/cm2.