Effect of different photoactivation methods on the bond strength of composite resin restorations by push-out test

Objective: Modulated curing methods could lead to a higher probability of bond preservation. Therefore, the aim of this study was to evaluate the effect of 7 curing methods on bond strength of composite resin restorations. Method and Materials: Seventy bovine incisors were selected. A conical cavity was prepared in the buccal surface. Adper Single Bond adhesive system was applied according to the manufacturer's instructions, and the cavities were filled with a single increment of Esthet X (Dentsply/Caulk). The specimens were randomly assigned into 7 groups (n = 10) according to the photoactivation method: (1) continuous light 700 (700 mW/cm2) (control); (2) continuous light 150 (150 mW/cm2); (3) continuous light 250 (250 mW/cm2); (4) soft-start 75 (75 mW/cm2) + 700 mW/cm2); (5) soft-start 150 (150 mW/cm2 + 700 mW/cm2); (6) pulse-delay (150 mW/cm2 + 3 minutes + 700 mW/cm2); and (7) intermittent light (cycles at 600 mW/cm2). The energy density for all groups was 14 J/cm2. The bond strength of the composite restorations was measured by performing the push-out test in a universal testing machine (Instron). The results were submitted to ANOVA and Tukey test (P .05). Results: Pulse-delay, soft-start 150, and soft-start 75 methods showed a significant increase in bond strength when compared with the control continuous light 700 method. Low power density and intermittent light groups showed intermediate results. Conclusion: Modulation of the energy density during light curing of composite resins using pulse-delay or soft-start methods increased the bond strength of composite restorations. Keywords: bond strength, composite resin restorations, photoactivation methods, power density, pulse-delay, push-out test, soft-start polymerization