Post-gel Shrinkage Strain and Degree of Conversion of Preheated Resin Composite Cured Using Different Regimens

Objectives: This study investigated the influence of resin composite preheating temperature, light curing regimen (mode and duration) on post-gel shrinkage strain (PGSS) and degree of conversion (DC) of a restorative resin composite. Methods: A hybrid resin composite preheated to three different temperatures (37 degrees C, 54 degrees C and 68 degrees C) was cured using a high intensity light emitting diode (LED) curing unit. The light source was used in 40- and 20-second continuous mode as well as soft start mode. The resin composite was monitored for PGSS during curing and 10 minutes following light irradiation using strain gauges. DC was measured using FTIR spectrometer. The results were analyzed using two-way ANOVA followed by the Duncan's Multiple Range Test for pairwise comparisons. The significance level was set at p <= 0.05. Results: Preheating of the resin composite significantly increased its PGSS and DC. The soft start groups revealed significantly lower PGSS values compared to the 20- and 40-second groups without altering the DC. Conclusions: Preheating of resin composite prior to curing increased its DC but also increased its PGSS. The soft-start mode decreased the PGSS of resin composite without altering the DC.