Effect of radiation therapy on the dentin bond strength of a universal adhesive

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.