Phase transformations in a leucite-reinforced pressable dental ceramic

The objectives of this study were to determine the conditions for the formation of sanidine in a pressable dental ceramic (OPC; Jeneric/Pentron). Ceramic discs (16 mm in diameter, 1.3 mm thick; n = 60) were pressed according to the manufacturer's recommendations. One group was left as pressed as the control; the other groups were further heat-treated at temperatures ranging from 700 degrees C to 1100 degrees C for times ranging from 10 min to 24 h. X-ray diffraction was performed on powdered specimens. The microstructure was investigated by scanning electron microscopy (SEM). X-ray diffraction showed that sanidine was the only crystalline phase present after heat treatment at 900 degrees C for 24 h, whereas a mix of tetragonal leucite and sanidine was found in the specimens heat-treated at 900 degrees C for 12 h and 800 degrees C for 24 h. Tetragonal leucite was the only phase present in the control specimens after heat treatment at 950 degrees C and higher, and in the specimens heat-treated up to 1 h at 850 degrees C or 900 degrees C. Tetragonal and cubic leucite were found in the specimens treated at 750 degrees C or 800 degrees C for 30, 60, and 180 min and 700 degrees C for 24 h. SEM confirmed the presence of sanidine in the specimens heat-treated at 900 degrees C for 24 h. All specimens treated for up to 20 min at temperatures ranging from 700 degrees C to 950 degrees CC contained only tetragonal leucite. The clinical significance of this study is that the formation of sanidine is unlikely to occur at the temperature and time ranges needed for the staining or veneering of this leucite-reinforced pressable dental ceramic.