Abstract
BACKGROUND: Successful restorative procedures, particularly for patients undergoing head and neck radiotherapy, rely on a robust adhesive interface. Since radiotherapy may alter dental tissues and compromise bonding, this study evaluated how the timing of radiation exposure affects the microtensile bond strength (µTBS) of a universal adhesive to dentin with different application modes. METHODS: Forty-two human third molars were used in this study. Mid-coronal dentin was prepared using a low-speed saw and polished with silicon carbide paper. The samples were randomly divided into 3 groups (n = 6) according to the timing of radiation exposure (no radiation, control; radiation after restoration, F-RT; and radiation before restoration, RT-F). A single radiation dose of 70 Gy was administered to the samples after restoration (F-RT) and before restoration (RT-F). The samples were further divided into 2 subgroups according to the application mode of a universal adhesive (Single Bond Universal adhesive, 3 M Oral Care, St. Paul, MN, USA): etch-and-rinse (ER) or self-etch (SE) mode. After adhesive application, the resin composite was constructed and stored in distilled water at 37 °C for 24 h. Six resin-bonded teeth per group were processed for the µTBS test. The data were analyzed by two-way ANOVA followed by Duncan's test (p < 0.05). Fractured surfaces were observed under a scanning electron microscope (SEM). Additional teeth were prepared for resin‒dentin interface observation (n = 1) and observed using an SEM. RESULTS: The application mode of the universal adhesive had no influence on the µTBS of dentin, regardless of irradiation (p = 0.670). The µTBS values of the control groups were not significantly different from those of the F-RT group but were significantly higher than those of the RT-F group for both application modes. The resin‒dentin interfaces of the samples were similar among the control, F-RT and RT-F groups. More abundant and longer resin tags were observed when the universal adhesive was bonded in ER mode. CONCLUSION: Compared with radiation after restoration, radiation before restoration resulted in an inferior bond strength. The application mode of a universal adhesive had no effect on the bond strength. CLINICAL SIGNIFICANCE: Restoration prior to the radiation procedure is an advisable strategy.