Effect of P2O5 on the Thermal Properties and Flexural Strength of Lithium-Containing dental Glass-Ceramic

Objectives:The purpose of this study is to evaluate the effect the P2O5 content on the thermal properties and flexural strength of lithium-containing glass-ceramic in the SiO2-Li2O-K2O-Al2O3-P2O5 system. Methods:Four glass compositions were prepared,varying the P2O5 content from 0 wt% to 6 wt%.The compositions were melted at 1500°æ for 3 h and cast into 55µç10µç20mm blocks.Differential thermal analyses were performed on the glasses up to 1100°æ.Bares were cut from the glass-ceramic blocks heat-treated at various temperatures.The crystalline phases were analyzed by X-ray diffraction.Five specimens per glass compositions were tested using the three-point flexural strength test .The microstructure of the glass-ceramics were investigated from scanning electron microscopy. Results:Differential thermal analyses showed that the crystallization of these glasses occurred in the temperature range 500-850°æ.The main crystalline phase was lithium disilicate.Lithium metasilicate,lithium orthophosphate and quartz were secondary phases.Surface crystallization occurred in glasses with a P2O5 content of 0 wt%.Glass with a P2O5 content of 6wt% was opalescent. Adding 4.3 wt% P2O5 resulted in randomly oriented rod-shaped crystals in the volume of glass-ceramic.The mechanical strength of this glass-ceramic was 273 MPa. Conclusion:The glass containing 4.3 wt% P2O5 was most efficient in forming a fine volume crystallization glass-ceramic which was responsible for promising dental ceramics.