Evaluation of irrigation activation techniques for root canal filling material removal in retreatment of 3D-printed curved canals

This study aimed to evaluate the effect of canal curvature on the removal of root canal filling material using different irrigation activation techniques in nonsurgical endodontic retreatment. A total of 117 standardized replica maxillary incisor teeth were fabricated using a three-dimensional (3D) printer and obturated with GuttaFlow. The samples were randomly assigned to nine groups ( n = 13 per group) according to canal curvature (15°, 30°, and 45°) and irrigation protocol: conventional needle irrigation (CNI), sonic activation (EDDY), or ultrasonic irrigation activation (UIA). The residual filling material in the entire canal and apical third was quantitatively assessed as absolute volume (mm³) using cone-beam computed tomography (CBCT) and 3D Slicer software, and percentage values (%) were subsequently calculated relative to the total canal volume. Data were analyzed using two-way analysis of variance (ANOVA) and Kruskal–Wallis tests ( p < 0.05). Canal curvature significantly affected the volume of residual filling material (F = 16.40, p < 0.001), with greater curvature associated with greater residual volume. The mean residual volume in the apical third increased from 0.51 mm³ (7.82%) in the 15° group to 1.80 mm³ (27.60%) in the 45° group. No significant differences were observed among irrigation techniques (F = 2.44, p = 0.094). Canal curvature plays a decisive role in retreatment efficacy, particularly in the apical third, whereas the contribution of irrigation activation techniques appears limited under standardized conditions. Clinicians should consider canal curvature as a primary factor influencing retreatment outcomes and adapt irrigation strategies accordingly, especially in highly curved canals.