The effects of maturity and dehydration shrinkage on resin-modified glass-ionomer restorations

The dimensional change, including hygroscopic change, of adhesive dental 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 environment; depending on the surroundings, they can gain or lose water, either of which can be potentially damaging. These effects become less noticeable as the cement ages. The effects of maturity of the newer resin-modified glass-ionomer materials and their responses to changes in moisture are unknown. Using confocal microscopy, we examined the effects of dehydration stress on the glass-ionomer/tooth interface in specimens of various degrees of maturity. Wedge-shaped cervical cavities in extracted teeth were restored with one of three resin-modified glass-ionomer restorative materials. The control specimens were restored with a conventional glass ionomer. The samples were left to mature, then sectioned 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 confocal microscope with water-immersion objectives so that the subsurface interfacial characteristics could be studied. The specimen was then allowed to dehydrate under the microscope, with further examinations at 15, 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 mechanisms involved. All of them were susceptible to dehydration shrinkage up to 3 mos of maturity. At 6 mos and 1 yr, Fuji II and Fuji II LC showed insensitivity to dehydration. Vitremer and Photac-Fil showed less sensitivity to dehydration at 1 yr than at 6 mos. The results of this study of the maturing polymerized resin-modified cements have potential clinical implications in the handling of these materials; the addition of resin has not significantly reduced the glass ionomer's susceptibility to dehydration problems.