Effect of a Two-step Placement Procedure on the Dislocation Resistance of a Methacrylate Resin-based Root Canal Sealer: A Proof of Concept

Purpose: To investigate whether the placement of a methacrylate root canal sealer or a conventional epoxy root canal sealer in two steps increases their dislocation resistance when compared to a one-step placement procedure. Materials and Methods: Eighty single-rooted teeth were randomly allocated to 4 groups (n = 20). All canals were instrumented to size 40, 0.06 taper and irrigated according to a standardized protocol. Root canal filling was conducted as follows: group 1: methacrylate sealer placed in two steps; group 2: methacrylate sealer placed in one step; group 3: epoxy sealer placed in two steps; group 4: epoxy sealer placed in one step. After setting, thin slices at different root levels were obtained and submitted to push-out testing. Results were analyzed with non-parametric tests to compare the two-step procedures to their one-step counterparts. Failure modes were determined by stereomicroscopy. Random untested methacrylate sealer specimens were also examined with scanning electron microscopy. Results: At each root level, dislocation resistance was significantly higher for the two-step procedure than for the one-step procedure using the methacrylate sealer (p = 0.003, p = 0.005, p 0.001) but not the epoxy sealer (p = 0.83, p = 0.1, p = 0.06). Among root levels, there were no significant differences in dislocation resistance in the methacrylate sealer two-step group, while all other groups showed differences. Conclusion: A two-step placement procedure resulted in significantly higher dislocation resistance for the methacrylate sealer but not for the epoxy sealer. Keywords: adhesion, configuration factor, dislocation resistance, methacrylate resin, polymerization shrinkage, root canal sealer