Post-gel polymerization shrinkage associated with different light curing regimens.

This study compared post-gel polymerization shrinkage associated with five different light curing regimens of similar light energy density. A light-cure unit (VIP, BISCO) that allowed for independent command over time and intensity was used. The five regimens investigated were pulse delay (PD), soft-start (SS); pulse cure (PC), turbo cure (TC) and standard continuous cure (C) [control]. With the exception of TC, the light energy density for all curing regimens was fixed at 16 J/cm2. A strain-monitoring device and test configuration were used to measure the linear polymerization shrinkage of 2-mm thick composite specimens (Z100, 3M ESPE) during and post-light polymerization up to 60 minutes. Five samples were made for each curing mode. The results were analyzed using ANOVA/Scheffee's post-hoc test at significance level 0.05. Post-gel shrinkage ranged from 0.30% to 0.46 % at 60 minutes. The use of PD resulted in significantly lower shrinkage compared to PC, TC, SS and C. Shrinkage associated with SS was, in general, significantly lower than C. No significant difference in shrinkage was observed between PC, TC and C at all time intervals. The use of pulse delay and soft-start regimens decreased post-gel polymerization shrinkage.