Devitrification of ionomer glass and its effect on the in vitro biocompatibility of glass-ionomer cements

The effects of devitrification of an ionomer glass with a molar composition 4.5SiO2•3Al2O3•1.5P2O5•3CaO•2CaF2 on cement formation and in vitro biocompatibility were investigated. Differential thermal analysis was used to study the phase evolution in the glass, and to determine the heat treatments for production of glass-ceramics. X-ray diffraction patterns from glass frit heat-treated at 750°C for 2 h contained peaks corresponding to apatite (JCPDS 15-876), whereas for samples heat-treated at 950°C for 2 h apatite and mullite (JCPDS 15-776) were the major phases detected. Transmission electron microscopy (TEM) confirmed that apatite and apatite–mullite phases were present after heat treatments at 750°C and 950°C respectively. Glass and glass-ceramics were ground to prepare <45 μm powders and glass ionomer cements were produced using a ratio of 1 g powder: 0.2 g PAA: 0.3 g 10% m/v tartaric acid solution in water. In vitro biocompatibility was evaluated using cultured rat osteosarcoma (ROS) cells. Scanning electron microscopy (SEM) showed that cells colonised the surfaces of cements prepared using untreated ionomer glass and glass crystallised to form apatite (750°C/2 h). However, quantitative evaluation using MTT and total protein assays indicated that more cell growth occurred in the presence of cements prepared using ionomer glasses crystallised to apatite than cements prepared using untreated glass. The least cell growth and respiratory activity was observed on cements made with crystallised glass containing both apatite and mullite. It was concluded that the controlled devitrification of ionomer glasses could be used to produce GIC bone cements with improved biocompatibility.