Delayed light activation of resin composite affects the bond strength of adhesives under dynamic simulated pulpal pressure

Objective: To evaluate the effect of a time delay before the light activation of resin composite on the microtensile bond strength (µTBS) of self-etch adhesives under dynamic simulated pulpal pressure. Materials and methods: One hundred twenty crown segments were prepared from human third molars. Dentin surfaces were prepared with coarse diamond burs and connected to a dynamic pulpal pressure device. The self-etch adhesives used were Clearfil SE Bond (CSE), G2-Bond Universal (G2B), Clearfil Universal Bond Quick (CBQ), and G-Premio Bond (GPB). Each adhesive was divided into 3 subgroups: immediate light activation of resin composite (T₀), delayed light activation for 150 s (T₁), and 300 s (T₂). The µTBS data were obtained after 24-h water storage. Scanning electron microscopy was used to evaluate the nanoleakage at the resin–dentin surface. The µTBS data were analyzed using two-way ANOVA and Duncan’s multiple comparisons. Results: All adhesives demonstrated a significant reduction in µTBS at T₂, except for CBQ where the bond strength was not affected by the delayed light activation times. The two-step self-etch adhesives (CSE and G2B) demonstrated higher bond strength than the one-step adhesives at all conditions. Nanoleakage was observed in all adhesives at T₂; however, nanoleakage was detected only in CBQ and GPB at T₁. Conclusions: Delayed light activation of resin composite adversely affected the dentin bond strength of self-etch adhesives. Two-step self-etch adhesives had better bonding performance than one-step self-etch adhesives. Clinical relevance: After adhesive application, resin composite should be adapted and cured as soon as possible.