lthough the success of endodontic treatments is high (greater than 90%), failure may occur sometimes after endodontic therapy. 1 The most common causes are continued microbial infection within the root canal system or periapical region, related poorly treated root canals, or coronal leakage. 2-4 When endodontic therapy fails, nonsurgical endodontic retreatment requires treating the infection by removing obturation material, debris, and microorganisms. 5,6 The most common root canal filling material