Polymerization contraction stress of low-shrinkage composites and its correlation with microleakage in class V restorations

Objective. The aim of this study was to compare the behavior of two new, low-shrinkage hybrid composites (Aelite LS and Inten-S) with a microfilled (Heliomolar) and a hybrid composite (Filtek Z250), in terms of polymerization contraction stress and microleakage. Methods. Maximum contraction stress after 10 min was recorded in a ‘tensilometer’, using a C-factor (C) of 2.5 and energy density of 26 J/cm2. For the microleakage test, cylindrical cavities with enamel margins prepared in bovine incisors (4 mm diameter, 1.5 mm depth, C=2.5) were restored in bulk, applying the same energy density used in the contraction stress test. After immersion in 0.5% methylene blue for 4 h, specimens were sectioned twice, perpendicularly, and the highest dye penetration score was recorded. Contraction stress results were analyzed by one-way ANOVA/Tukeyʹs test and microleakage was analyzed by Kruskal–Wallis test. Regression analysis between the two variables was also performed. Results. Aelite LS showed significantly higher stress than the other composites tested. Inten-S and Filtek Z250 had similar stress levels, statistically higher than Heliomolar. In the microleakage test, a significant difference was observed between Aelite LS and Heliomolar only. Regression analysis showed a good linear correlation between the two variables (R2adjusted=0.811). Conclusions. The low-shrinkage materials exhibited contraction stress values similar or higher than the hybrid composite. A direct relationship between contraction stress values and microleakage for the composites evaluated was verified. Significance. The low-shrinkage composites tested did not seem to represent an improvement in terms of reducing contraction stress or microleakage.