Heat-pressed ionomer glass-ceramics. Part I: an investigation of flow and microstructure

Objectives. This study investigated a series of ionomer glasses based on the formula: 4.5SiO2–1.5P2O5–(X)Al2O3–4.5CaO–0.5CaF2, where X was varied from 3.0 to 1.5. The possibility of processing ionomer glasses using a heat-pressing method for dental restorations was investigated. Methods. A simple flow test was designed to measure the amount of flow the glasses underwent as a result of heat-pressing at 1150 °C for different times. Heat-pressed samples of the X=3.0, 2.8, 2.4 and 2.0 glass were further heat-treated for 1 and 4 h at 1150, 1200 and 1250 °C to promote crystal growth. Scanning electron microscopy was used to investigate the microstructure of the glass-ceramics. X-ray diffraction was used to identify the crystalline phases in the glass-ceramics. Results. The ionomer glasses exhibited excellent flow ability. Crystallization could not be suppressed during heat-pressing. Very fine scale fluorapatite crystals were present in all of the samples after heat-pressing. Mullite and/or anorthite formed as a second crystal phase. On further heat-treatment of the samples, changes in crystal phases took place. Significance. Apatite was the main crystalline phase produced in the glass-ceramics; this factor is of clinical significance. In conclusion these glass-ceramics could be suitable for all-ceramic dental restorations.