The effect of different curing units on the degree of polymerization of different composite resins

Objective: The aim of this study was to investigate the degree of polymerization of composite resins cured with different light-curing units (LCUs). Materials and Methods: Three bulk-fill composite (Beautifil Bulk-Fill Giomer, Filtek Bulk-Fill, and X-Tra Fill) and a methacrylate-based composite (Filtek Z250) were used in this study. Thirty disc-shaped specimens, 4 mm thick, were prepared from each composite resin. Specimens were divided into three groups and polymerized with light-emitting diode (LED), Plasma arch curing unit (PAC), and quartz-tungsten halogen LCU. The bottom and top surface microhardness of the specimens stored in distilled water for 24 h at 37°C after polymerization was measured with a universal test device. The hardness ratio (HR) of specimens was calculated by the bottom surface microhardness/top surface microhardness formula. Data were analyzed by two-way ANOVA and Tukey's least significant difference post hoc tests (α = 0.05). Results: Statistically significant differences were detected between the mean HR values of the specimens polymerized with different LCUs (P < 0.05). The mean HR values of Beautifil Bulk-Fill Giomer specimens were found to be statistically significantly lower than other composites (P < 0.05). The mean HR values of the specimens polymerized with PAC LCU were found to be statistically significantly lower than other LCUs (P < 0.05). Conclusion: The degree of polymerization of the composite resin restoration may be affected by the structural properties of the resin and the type of LCU. The clinician may use alternative techniques, especially in deep cavities.