Effect of Retreatment Protocols on the Push‐Out Bond Strength of Hydraulic Calcium Silicate Cement in Open‐Apex Teeth

Objectives During retreatment, complete removal of previous obturation materials is essential, as remnants may compromise adhesion. This study evaluated the effect of four retreatment protocols on the push‐out bond strength of RetroMTA (BioMTA, Seoul, Korea), a fast‐setting calcium silicate–based material, used as an apical barrier in teeth with open apices that had been previously obturated with gutta‐percha and AH26 sealer. Materials and Methods Sixty extracted single‐rooted human teeth were instrumented and obturated using lateral condensation and then stored in phosphate‐buffered saline (PBS) at 37°C for 4 weeks. Specimens were randomly assigned to four groups ( n = 15): mechanical retreatment, mechanical retreatment with passive ultrasonic irrigation (PUI), chloroform‐assisted retreatment, and chloroform‐assisted retreatment with PUI. After retreatment, the apical 5 mm of each canal was obturated with RetroMTA and stored for another 4 weeks. Push‐out bond strength was measured using a universal testing machine. Data were analyzed using two‐way ANOVA. The significance level was set at α = 0.05. Results Chloroform use did not significantly affect the push‐out bond strength of RetroMTA ( p = 0.349). In contrast, PUI significantly increased bond strength regardless of solvent use ( p < 0.001). No significant interaction was observed between chloroform and PUI. Conclusion Within the limitations of this ex vivo study, PUI significantly enhanced the bond strength of RetroMTA to root dentin, whereas chloroform provided no additional benefit.