POLYMERIZATION SHRINKAGE OF COMPOSITE RESINS - COMPARISON WITH TOOTH DEFORMATION

Polymerization shrinkage of two posterior composite resin restorative materials was measured by dilatometry. The results were compared with a decrease in cavity width of MOD preparations in extracted premolars restored with the composite resins. A highly filled hybrid composite e xhibited greater free shrinkage and cuspal deformation than a hybrid c omposite with a lower filler content. Deformation of the cusps was les s than the unrestricted shrinkage of the composite resins. Hydrated te eth exhibited less deformation than dehydrated teeth because of polyme rization shrinkage. Greater cuspal deformations were measured with the microscopic technique than with interferometry because of differences in experimental design.