Effect of preheating on polymerization shrinkage strain of BIS-GMA free and containing resin composite restorative materials (in vitro study)

Abstract

Background: This study investigated the effect of preheating of bulk-fill BIS-GMA free and containing resin composite on post-gel shrinkage strain. In a split Teflon mold, sixty resin composite specimens were prepared with dimensions 7 mm length × 4 mm width × 4 mm height. Thirty specimens of each tested restorative materials were prepared , ten specimens for each selected temperature used in the study (room temperature 23 °C, 50 °C and 65 °C). The resin composite was monitored for post-gel shrinkage strain for 3 min after light irradiation using strain gauges. For pairwise comparisons, Duncan's multiple range test was used to analyze the data after two-way ANOVA. The p ≤ 0.05 significance level was chosen. Results: Viscalor thermoviscous bulk-fill composite Bis-GMA containing had the lowest polymerization shrinkage strain values in the three different temperatures. There was a statistically significant difference between groups according to material used at different temperatures. Both tested materials showed the highest shrinkage strain when preheated at 65 °C. Conclusions: While the technology of thermoviscous is introduced to deliver the viscosity of a flowable resin composite so reducing the polymerization strain, it actually had adverse effect on it. Preheating of bulk-fill BIS-GMA free resin composite either to 50 °C or 65 °C had no effect on decreasing the polymerization shrinkage strain. Polymeriza-tion shrinkage strain of bulk-fill BIS-GMA contains resin composite either without or with preheating far superior to that of BIS-GMA free resin composite.