THE EFFECTS OF MATURITY AND DEHYDRATION SHRINKAGE ON RESIN MODIFIED GLASS-IONOMER RESTORATIONS

The dimensional change, including hygroscopic change, of adhesive dent al materials is a clinically important topic, since excessive changes could cause debonding from tooth structure. The water balance of glass -ionomer cements arises mainly from their sensitivity to the environme nt; depending on the surroundings, they can gain or lose water, either of which can be potentially damaging. These effects become less notic eable as the cement ages. The effects of maturity of the newer resin-m odified glass-ionomer materials and their responses to changes in mois ture are unknown. Using confocal microscopy, we examined the effects o f dehydration stress on the glass-ionomer/tooth interface in specimens of various degrees of maturity. Wedge-shaped cervical cavities in ext racted teeth were restored with one of three resin-modified glass-iono mer restorative materials. The control specimens were restored with a conventional glass ionomer. The samples were left to mature, then sect ioned and examined at 1 day, 1 wk, 1 mo, 3 mos, 6 mos, and 1 yr. After being sectioned, each specimen was examined immediately with a confoc al microscope with water-immersion objectives so that the subsurface i nterfacial characteristics could be studied. The specimen was then all owed to dehydrate under the microscope, with further examinations at 1 5, 30, and 60 min. Generally, gap formation at the interface occurred within 15 min of dehydration. All materials showed a different pattern of gap change with maturity, probably due to the different setting me chanisms involved. All of them were susceptible to dehydration shrinka ge up to 3 mos of maturity. At 6 mos and 1 yr, Fuji IT and Fuji II LC showed insensitivity to dehydration. Vitremer and Photac-Fil showed le ss sensitivity to dehydration at 1 yr than at 6 mos. The results of th is study of the maturing polymerized resin-modified cements have poten tial clinical implications in the handling of these materials; the add ition of resin has not significantly reduced the glass ionomer's susce ptibility to dehydration problems.