The Effect of Radiotherapy on the Microtensile Bond Strength of Dentin in Relation to the Timing of Restoration Procedure.

OBJECTIVE: To compare microtensile bond strength at different time points relative to fractional irradiation using both etch-and-rinse (ER) and self-etch (SE) adhesive systems. METHODS: Ninety-six sound extracted human molars were divided into two control groups (control-ER and control-SE) and six irradiated groups. The irradiated groups were subdivided based on the timing of restoration: those restored before irradiation (restoration before irradiation [RBI]-ER and RBI-SE) and those restored after irradiation (irradiation before restoration [IBR]-ER, IBR-ER delayed, IBR-SE, and IBR-SE delayed). The irradiated specimens underwent fractional radiotherapy at 2 Gy per day, reaching a total dose of 70 Gy. All specimens were restored with resin composite at the designated time points relative to irradiation. Microtensile bond strength was measured, fracture patterns were analyzed, and surface morphology was examined using scanning electron microscopy (SEM). Data were analyzed using two-way ANOVA followed by Bonferroni post hoc tests (α = 0.05). RESULTS: ANOVA revealed significant restoration timing and adhesive-type effects on microtensile bond strength (p < 0.01). Post hoc analysis showed that irradiation reduced bond strength (p < 0.01). In irradiated ER groups, the RBI group had lower bond strength than post-irradiation restorations (p < 0.01), while in SE groups, bond strength did not vary across time points (p > 0.05). Additionally, significant differences were found in the IBR and IBR delayed groups, with the ER adhesive outperforming the SE adhesive with a (p < 0.05). CONCLUSIONS: Irradiation compromised dentin bond strength, resin tag formation and hybrid layer integrity in a manner dependent on the adhesive system used. In the ER adhesive groups, bond strength was significantly higher when restorations were performed post-irradiation. Conversely, for the SE adhesive groups, the time points of the restoration had no significant effect on bond strength.