Contraction stress and marginal adaptation of composite restorations in dentinal cavity

The influence of contraction stress in composite resins on both the shear bond strength to dentin (BS) and marginal adaptation in a standardized dentin cavity was investigated using three restorative resin systems. A teflon ring mold (TF) or copper ring with a roughened inner surface (CP) placed on human tooth dentin was filled with the composite resin, and a shearing test was then performed. ANOVA of BS demonstrated a significant influence from the resin systems and type of molds. BSCP tended to be lower than BSTF in all three systems. This suggested that the inner surface of the CP restricted the flow of resin and then contraction stress occurred at the interface of the bond to the dentin. The system which demonstrated the smallest difference between BSTF and BSCP also showed the best adaptation. This result indicates that contraction stress in the composite resin plays an important role in marginal adaptation.