Phase transformations in a leucite-reinforced pressable dental ceramic

The objectives of this study were to determine the conditions for the forma tion of sanidine in a presablee dental ceramic (OPC(R); Jeneric/Pentron) Ce ramic discs (16 mm in diameter, 1.3 mm thick; n = 60) were pressed accordin g to the manufacturer's recommendations. One group was left as pressed as t he control; the other groups were further heat-treated at temperatures rang ing from 700 degreesC to 1100 degreesC for times ranging from 10 min to 24 h. X-ray diffraction was performed on powdered specimens. The microstructur e was investigated by scanning electron microscopy (SEM). X-ray diffraction showed that sanidine was the only crystalline phase present after heat tre atment at 900 degreesC for 24 h,whereas a mix of tetragonal leucite and san idine was found in the specimens heat-treated at 900 degreesC fur 12 h and 800 degreesC for 24 h. Tetragonal leucite was the only phase present in the control specimens after heat treatment at 950 degreesC and higher, and in the specimens heat-treated up to 1 h at 850 degreesC or 900 degreesC. Tetra gonal and cubic leucite were found in the specimens treated at 750 degreesC or 800 degreesC for 30, 60, and 180 min and 700 degreesC for 24 h. SEM con firmed the presence of sanidine in the specimens heat-treated at 900 degree sC for 24 h. All specimens treated for up to 20 min at temperatures ranging from 700 degreesC to 950 degrees CC contained only tetragonal leucite. The clinical significance of this study is that the formation of sanidine is u nlikely to occur at the temperature and time ranges needed for the staining or veneering of this leucite-reinforced pressable dental ceramic. (C) 2000 John Wiley & Sons, Inc. J Biomed Mater Res 54: 351-359, 2001.