Microshear bond strength of conventional and bioactive restorative materials to irradiated and non-irradiated dentin: an in vitro study

Purpose: To evaluate the effect of conventional and bioactive restorative materials on bond strength to control (non-irradiated) and irradiated dentin. Methods: Human dentin fragments (240) were polished and divided into non-irradiated dentin (NI; n = 120) and irradiated dentin (ID; n = 120). ID specimens received 70 Gy irradiation (2 Gy/fraction, 5 days/week for 7 weeks). All dentin surfaces were bonded to restorative materials with Scotchbond universal adhesive in self-etching mode. Microshear bond strength cylinders were built on the bonded surface according to the restorative material (4 subgroups, n = 30): conventional resin composite (CC-Filtek Z250) and three bioactive restorative composites (BCI-Activa BioActive-Restorative; BCII-Beautiful II; BCIII-Predicta Bulk). Specimens were stored in water at 37 °C for 24 h or 30 days and subjected to microshear bond strength test. The data was analyzed using two-way ANOVA and Tukey's post-hoc test (⍺ < 0.05). The morphological surface of both NI and ID dentin (n = 3) was analyzed using Scanning Electron Microscopy (SEM). Results: Two-way ANOVA revealed a significant effect of the Time/Radiation (p < 0.001). Restorative material (p = 0.191) and the interaction Time/Radiation*Restorative material (p = 0.169) were not significant. Irradiation decreased the bond strength of CC specimens at both 24 h (p < 0.001) and 30 days (p < 0.001). None of the bioactive materials were significantly affected by irradiation and storage time. The SEM analysis revealed morphological changes in the ID specimens. Conclusion: Ionizing radiation-induced morphological changes in the dentin surface. These changes negatively affected the conventional resin composite bond strengths to dentin. However, these morphological alterations did not affect the bond strength of the bioactive restorative materials.