The complex morphology of the root canal system causes the canal instrumentation to face challenges. Perforation, apical transportation, and ledge formation are some of the errors that may be encountered during the instrumentation of canals with a double curvature or S-shape. Therefore, it is necessary to determine the curvature of the canal before starting the RCT (21). To avoid these errors, the basic principles of RCT should be followed. Proper radiography, obtaining SLA, precurving the files, adequate irrigation, and most importantly using Ni-Ti instrumentation systems (22).
The broken file in the third case of the present study led to more challenging RE root canal therapy. One of the most important factors in managing the retrieval of a broken file depends on the location of the instrument separation (23). The current study used the loop technique and bypass to manage two broken files. The success of the bypass method, especially in the more apical spots, has been emphasized in previous studies (24), and the use of removal kits with a loop system shows promising results (25, 26).
In the present study, three cases of RE were discussed. Management of RE treatment requires special care that should be considered within the framework of the RCT basic principles. In addition to the management of RE treatment, canals with double curvature or S-shapes add to the treatment challenges, which may lead to errors such as broken files, which were also noted in the present study. Therefore, prior knowledge of the morphological characteristics of the possible anatomical variations, the appropriate use of clinical or paraclinical tools, and increasing technical sensitivity are essential for preoperative planning and effective therapeutic intervention.