THE HYDRATION OF AN ION-LEACHABLE GLASS USED IN GLASS-IONOMER CEMENTS

A study is reported in which the interaction between a typical ionomer glass and water was evaluation in order to evaluate the importance of hydration in the setting of glass-ionomer cements. Glass G338 was mixed with water and the slurries were allowed to harden in metal moulds to create cylindrical specimens 6 mm high x 4 mm diameter. Samples of these specimens were found to disintegrate when placed in water. Following hardening at 37 degrees C for 1 hour in the moulds, one series of specimens was stored at 95 % RH for 23 h, 1 week and 4 weeks, and the other stored for the same lengths of time, but sealed in the moulds. Raman spectra were recorded for glass G338 and glass-water blends stored for 24 hours and 4 weeks. The cylindrical specimens were found to have a degree of structural integrity, but proved to be extremely weak in compression (all specimens of whatever age zip to 4 weeks having strengths of less that 1 MPa). Specimens lost mass on storage at 95 % RH. Raman spectra showed no additional bands due to glass-water interactions compared with the dry glass itself, and changes in intensity were difficult to interpret, due to Fermi resonance in the regions of interest. It is concluded that binding in these specimens is due to hydrogen bonding between layers of water adsorbed onto glass powder surfaces.