Contraction Stresses of Composites And Influence on Marginal Cavity Adaptation

Objective: The aim of this study was to determine the volumetric polymerization contraction stress of packable composites (ALERT, Surefil, Solitaire) and a packable ORMOCER material (Definite) in comparison with a conventional hybrid composite (Tetric Ceram). Method: The volumetric shrinkage measurements were performed by mercury dilatometry, and the contraction stress and tensile modulus were determined by means of stress–strain analysis. The statistical analysis was conducted by ANOVA and Tukey's post hoc test, and linear regression. Results: Strong linear correlation for most resin composites were found for (i) contraction stress and shrinkage (ii) contraction stress and tensile modulus, and (iii) shrinkage and tensile modules. For most of the materials the unpolymerized resin content determines the amount of shrinkage, contraction stress and tensile modules. Maximum contraction stresses of the packable materials were highest for ALERT, followed by Definite, Solitaire and Surefil, and all were significantly higher than that of Tetric Ceram which showed the least values for contraction stresses. Conclusion: High contraction stress and rapid contraction force development can lead to failure of bond to tooth structure. This study suggested that, packable composite resins are less capable of reducing the contraction stress during the early setting stage, thus not superior in maintaining the bond with cavity walls compared to conventional hybrid composite Tetric Ceram.