Polymerization Kinetics of Conventional vs. Fiber-Reinforced Composites Using Rapid High-Intensity Photo-Activation

This in vitro study examined the effects of rapid high-intensity vs. conventional light-curing on real-time degree of conversion (DC) of conventional and fiber-reinforced resin composites. Two resin composites specifically designed for rapid high-intensity photo-polymerization (Tetric PowerFill, Tetric PowerFlow), two flowable fiber-reinforced composites (everX Flow, FibraFill Flow), and two condensable fiber-reinforced composites (everX Posterior, FibraFill DENTIN) were included. Photo-activation was performed using two protocols: 3 s at 3006 mW/cm² or 10 s at 1108 mW/cm². DC of 1.5 mm thick specimens (n = 6) was monitored for 5 min by real-time ATR-FTIR spectroscopy, and the maximum polymerization rate (R_DCmax) was determined. Data were analyzed using independent t-tests and ANOVA followed by Tukey's post hoc test (α = 0.05). DC at the end of the 5 min observation period ranged from 33.7 ± 0.9% (FibraFill DENTIN, 3 s) to 59.2 ± 0.3% (Tetric PowerFlow, 10 s). All composites exhibited a significantly higher DC with the 10 s curing protocol compared with 3 s high-intensity light-curing. Within both curing protocols, Tetric PowerFlow, everX Flow, and everX Posterior achieved the highest DC values, whereas FibraFill DENTIN showed the significantly lowest DC. R_DCmax was significantly higher with the 3 s protocol than with 10 s light-curing for all materials, with the significantly highest values recorded for Tetric PowerFill and Tetric PowerFlow. FibraFill DENTIN and FibraFill Flow exhibited the significantly lowest R_DCmax for both curing protocols. In conclusion, 3 s high-intensity photo-activation increased the polymerization rate but simultaneously reduced the degree of conversion of conventional and fiber-reinforced flowable and condensable resin composites compared with a conventional 10 s light-curing regimen.