Comparative Scanning Electron Microscopy (SEM) Evaluation of Advanced Irrigation Activation Techniques for Bioceramic Sealer Removal in Retreatment: An In Vitro Study

Background: Retreatment cases involving bioceramic (BC) sealers consistently present a major challenge, as residual sealer remnants hinder the efficient cleaning and shaping of the root canals. Removing these sealers is difficult with standard syringe irrigation. To overcome this limitation, irrigant activation techniques have been introduced to help clean otherwise inaccessible areas of the root canal system, particularly the apical third. Therefore, this study evaluated the percentage of canal cleanliness along the coronal, middle, and apical thirds of root canal walls using scanning electron microscopy (SEM) following different irrigant activation techniques: laser diode, sonic activation, and passive ultrasonic activation. Methodology: Eighty single-canal mandibular premolars with completely formed apices were selected. Primary endodontic treatment was performed using hand and rotary instruments, followed by obturation with gutta-percha and a BC sealer. After a four-month incubation period, retreatment was performed using ProTaper Universal Retreatment Files (Dentsply Maillefer, Tulsa, OK). The specimens were then randomly divided into four equal groups (n = 20) based on the irrigation activation protocol applied: Group I received conventional syringe irrigation; Group II received sonic activation; Group III received passive ultrasonic activation; and Group IV received laser diode activation. Following the activation protocols, the samples were sectioned longitudinally and prepared for SEM evaluation. The percentage of clean canal surface area in each third was quantified using ImageJ software. A one-way ANOVA was performed to compare the groups, followed by the Bonferroni post-hoc test for pairwise comparisons. Results: The percentage of cleaned canal surface area demonstrated statistically significant differences among all four groups across the apical, middle, and coronal regions (p < 0.0001). Group IV consistently exhibited the highest mean cleanliness values across all anatomical locations, followed sequentially by Group III and Group II, while Group I recorded the lowest values. Conclusions: Within the limitations of this study, none of the irrigant activation methods was capable of completely removing all root canal filling material. However, laser diode irrigation demonstrated the highest efficacy in removing BC sealer from root canals during retreatment.