DEHYDRATION AND REHYDRATION OF AN ION-LEACHABLE GLASS USED IN GLASS-IONOMER CEMENTS

Samples of the ionomer glass known as G338 have been heated at 240°C for 24 hours, after which they lost 1.19 % (Standard deviation 0.16%) of their original mass. This loss was attributed to removal of water, as both molecular water and the product of reaction of silanol groups to form siloxane bridges. Exposing samples of glass either to air at ambient humidity or to air at 95% relative humidity showed a degree of rehydration, but mass uptake did not approach the original mass loss in either case. It is suggested that this is because of the relatively difficulty in forming new silanol groups from the siloxane bridges. Glass-ionomer cements prepared from these glass samples with aqueous poly(acrylic acid) solution had different properties, depending on the glass used. Dehydrated glass gave cements which set faster but were weaker than those formed by as-received glass. The role of silanol groups in influencing reaction rate and promoting strength development is discussed.