Influence of Radiotherapy Timing on Sealer-Dentin Adhesion: A Confocal Microscopy and Push-Out Bond Strength Study.

PURPOSE: The purpose of this study was to evaluate the influence of radiotherapy timing on the dentinal tubule penetration and push-out bond strength of an epoxy resin-based sealer (AH Plus) and a bioceramic sealer (BioRoot RCS). METHODS AND MATERIALS: In total, 180 single-rooted sound human mandibular premolars were used and allocated to three main groups with different radiotherapy timings: Control (no irradiation), Before RT (irradiation prior to root canal obturation), and After RT (irradiation after root canal obturation). Subsequently, each group was subdivided into different sealer types: AH Plus and BioRoot RCS. For the Before RT and After RT groups, a cumulative dose of 60 Gy (6 weeks, 2 Gy per day, 5 days per week) was delivered. The dentinal tubule penetration depth was assessed using confocal laser scanning microscopy (n = 15), and the push-out bond strength was measured using a universal testing machine (n = 15). The data were analyzed using three-way ANOVA and Bonferroni tests (p 0.05). RESULTS: In the coronal thirds, the After RT group showed significantly lower tubule penetration and bond strength compared with the Control group for both sealers. In the apical thirds, BioRoot RCS was predominantly affected. The After RT group also showed significantly lower bond strength and tubule penetration than the Before RT group. These results were confirmed by the higher frequency of adhesive failures in the After RT group compared to the others. Finally, in the coronal thirds, AH Plus exhibited significantly higher bond strength than BioRoot RCS despite having lower dentinal tubule penetration. CONCLUSION: Radiotherapy timing significantly influenced sealer-dentin adhesion, varying by root canal levels and material types. Radiotherapy applied after obturation adversely affected the sealer-dentin interaction, resulting in reduced tubule penetration and bond strength, especially for BioRoot RCS.