Efficacy of Passive Ultrasonic Versus Sonic Irrigation for the Removal of Filling Material After Retreatment of Oval Canals: A Micro-CT Study

Objective: The aim of this study was to evaluate and compare the efficacy of two distinct irrigation techniques—passive ultrasonic (IrriSafe) and sonic irrigation (EndoActivator)—following the use of the D-Race retreatment system in oval-shaped root canals. Methods: Twenty-four mandibular incisors with a single oval-shaped canal were instrumented, obturated, and subsequently randomly assigned into two groups ( n = 12). Both groups underwent initial retreatment using the D-Race retreatment system. Following this, supplementary irrigation protocols were applied. Group 1 received passive ultrasonic irrigation (PUI) using the IrriSafe ultrasonic tip, while Group 2 was treated with sonic irrigation using the EndoActivator. Micro-computed tomography scans were performed at three time points: after root canal obturation, after the initial retreatment with the D-Race system, and after the supplementary irrigation protocols. Statistical analysis was conducted using the nonparametric Wilcoxon signed-rank and Mann–Whitney U tests, with the significance level set at 0.05. Results: Neither method resulted in complete elimination of the root canal filling material. However, both irrigation techniques enhanced canal cleanliness following the use of the D-Race system. Notably, PUI demonstrated superior effectiveness in the apical third of the root canal compared to sonic irrigation with the EndoActivator ( P = 0.043). Conclusion: Within the limitations of this study, PUI was more effective than sonic irrigation for removing the residual filling material from the apical third of oval canals during endodontic retreatment.