Effect of carbodiimide and chlorhexidine on the bond strength longevity of resin cement to root dentine after radiation therapy

Aim To evaluate the effect of carbodiimide (EDC) and chlorhexidine (CHX) on the bond strength (BS) of resin cement to root dentine of teeth submitted to radiotherapy. Methodology One hundred and twenty extracted maxillary canines were selected and assigned to 2 groups (n = 60): nonirradiated and irradiated (30 cycles of 2 Gy, total 60 Gy). Roots lengths were standardized, and canals were prepared and filled. Post spaces were then prepared, and the samples were redistributed according to dentine treatment (n = 20): saline solution (SF); CHX 2%; or EDC 0.5M. After drying the post space, fibreglass posts were cemented. Cross-sectioned slices were obtained, and in half of the specimens of each subgroup (n = 10), the analysis was performed immediately; the others (n = 10) were stored for 10 months before analyses. The most cervical slice of each third was subjected to a push-out test and failure pattern analysis (n = 10), and the most apical slice submitted to the analysis of the adhesive interface by SEM (n = 5). The bond strength data were submitted to anova and Tukey tests, the adhesive interface adaptation was submitted to Kruskal-Wallis and Dunn's tests, and the Chi-square test was used to evaluate the type of failure. Results The irradiated specimens had significantly lower bond strength (13.8 +/- 4.3) than the nonirradiated (18.1 +/- 3.1; P < 0.001). For the irradiated teeth, the bond strengths were significantly lower in the SF and CHX groups (P < 0.001). Also, the bond strengths reduced significantly after 10 months in the SF and CHX groups (P < 0.001). Cohesive failures occurred in dentine for irradiated specimens. Poorer interface adaptation, dentine fractures and microfractures were observed in irradiated specimens, and better adaptation was observed for specimens after EDC treatment. Conclusions Radiotherapy was associated with lower bond strength and worse interface adaptation. Dentine treatment with EDC contributed to adhesive interface longevity during the cementation of glass fibre posts in nonirradiated and irradiated teeth.