Influence of different drying protocols on bond strength of epoxy resin- and calcium silicate- based root canal sealers in nonsurgical retreatment

BACKGROUND: The condition of root canal dentin and the drying protocol applied prior to obturation may influence the bonding performance of root canal sealers, particularly in retreatment cases where dentin characteristics are altered. This study aimed to evaluate the effect of different drying protocols on the push-out bond strength of epoxy resin- and calcium silicate-based sealers in primary root canal treatment and nonsurgical retreatment. METHODS: A total of 192 extracted human mandibular premolars were prepared and randomly allocated into groups according to drying protocol (paper point, EndoVac, ethanol, irrigation needle), sealer type (AH Plus, AH Plus Bioceramic), and treatment type (primary vs. retreatment). In retreatment groups, canals were re-prepared to a larger apical size (X4) without the use of solvents. After obturation, specimens were sectioned into coronal, middle, and apical slices, and push-out bond strength (MPa) was measured. Data were analysed using a four-factor linear mixed-effects model with tooth as a random effect. Post hoc comparisons were performed using Tukey adjustment (α = 0.05). RESULTS: Bond strength values generally increased from the coronal to the apical region across all groups. Retreatment specimens exhibited higher bond strength values than primary treatment, particularly in the apical region based on estimated marginal means (6.29 ± 0.35 vs. 2.78 ± 0.35 MPa). Ethanol drying yielded higher bond strength values in several apical conditions compared with other drying methods. No significant differences were observed between AH Plus and AH Plus Bioceramic within the coronal, middle, or apical regions (P > .05). Linear mixed-effects analysis demonstrated significant effects of treatment type (P < .001), root section (P < .001), and drying protocol (P = .001), whereas sealer type showed no significant main effect (P = .669). Significant interactions were identified between treatment type and root section, drying protocol and root section, and among treatment type, sealer type, drying protocol, and root section (P = .003). Cohesive and mixed failures predominated across experimental groups. CONCLUSIONS: Bond strength of root canal sealers is primarily influenced by root section and treatment condition, with drying protocol playing a secondary but context-dependent role. Retreatment procedures may enhance bond strength, particularly in the apical region, while sealer type alone does not significantly affect bonding performance.