Effect of Different Apex Locators on Postoperative Pain in Endodontic Retreatment of Single-Rooted Teeth: Prospective Randomized Clinical Study

Nonsurgical endodontic retreatment is a vital procedure that promotes periapical healing by eliminating previous root canal fillings, necrotic tissue, and residual microorganisms, thanks to the comprehensive cleaning of the root canal system \[1\]. The successful disinfection of intricate anatomical structures, such as dentinal tubules, lateral canals, and isthmuses, largely depends on the effective removal of obturation materials \[2\]. Even in the absence of coronal leakage or recurrent caries, persistent clinical symptoms or radiographic evidence of periapical pathology may indicate treatment failure, warranting retreatment \[3\]. Residual bacteria and remnants of root filling materials are known contributors to posttreatment disease \[4\]. A key factor in the success of both primary endodontic treatment and retreatment is the accurate determination of working length (WL), which dictates the apical extent of canal instrumentation and obturation \[5\]. Inadequate WL may result in over-instrumentation, leading to periapical irritation and postoperative pain \[6\]. WL is generally defined as the distance from a coronal reference point to the location where canal cleaning, shaping, and filling should ideally terminate, often coinciding with the apical constriction, and occasionally with the cementodentinal junction, where pulpal and periodontal tissues transition \[5\]. Although periapical radiographs are still commonly used for WL determination, they do not always provide definitive results due to certain limitations. Factors such as improper film placement, angular distortion, image magnification and distortion, patient exposure to ionizing radiation, and the superimposition of anatomical structures can compromise the accuracy of measurements \[7\]. As a result, electronic apex locators (EALs) have gained prominence as a dependable and objective tool for determining WL, offering real-time measurements less influenced by operator variability or anatomical distorti