This randomized controlled clinical trial aimed to evaluate the effect of different integrated electronic apex locator (EAL) modes on postoperative pain following nonsurgical endodontic retreatment. A total of 144 patients requiring retreatment of mandibular premolar teeth with periapical lesions were randomly assigned to four groups.

In the control group, working length was determined using a conventional electronic apex locator. In the experimental groups, an integrated EAL motor was used with three different modes: apical reverse, apical slow down, and apical stop.

All procedures were performed under standardized conditions. Postoperative pain was assessed using a numeric rating scale (NRS) at 6 and 12 hours and on days 1, 2, 3, 5, and 7 after treatment.

The study aimed to determine whether simultaneous working length control using integrated EAL modes influences postoperative pain compared with conventional working length determination.

Accurate determination and maintenance of working length is essential for successful endodontic retreatment. Electronic apex locators (EALs) are widely used to improve the accuracy of working length determination. Recently, endodontic motors with integrated EAL systems have been developed, enabling simultaneous working length control during canal instrumentation. These systems incorporate different automatic apical control modes, including apical reverse, apical slow down, and apical stop, which may influence clinical outcomes such as postoperative pain.

This randomized controlled clinical trial was conducted to evaluate the effects of different integrated EAL modes on postoperative pain following nonsurgical endodontic retreatment.

A total of 144 systemically healthy patients with previously treated single-rooted mandibular premolars diagnosed with asymptomatic apical periodontitis were included. Patients were randomly allocated into four groups (n=36 each): (1) conventional electronic apex locator (control group; Root ZX Mini), (2) integrated EAL motor with apical reverse mode, (3) apical slow down mode, and (4) apical stop mode (Ai Motor; Motopex; Woodpecker).

In the control group, working length was determined using a conventional EAL and confirmed radiographically. In the experimental groups, working length determination and instrumentation were performed simultaneously using an integrated EAL motor according to the assigned apical mode.

All retreatment procedures were completed in a single visit under standardized clinical conditions by a single experienced operator. Root canal filling materials were removed, canals were prepared using rotary instruments, and irrigation was performed using 2.5% sodium hypochlorite and 17% EDTA with ultrasonic activation. Final obturation was carried out using a single-cone technique with a bioceramic sealer.

Postoperative pain was assessed using an 11-point numeric rating scale (NRS) at 6 and 12 hours and on days 1, 2, 3, 5, and 7 after treatment. The primary outcome measure was postoperative pain intensity.

The study evaluated whether different simultaneous working length control strategies using integrated EAL modes affect postoperative pain compared with the conventional electronic apex locator method.

Inclusion Criteria:

• Systemically healthy patients aged between 18 and 65 years
• Patients requiring nonsurgical endodontic retreatment
• Single-rooted, single-canal mandibular premolar teeth
• Diagnosis of asymptomatic apical periodontitis
• Presence of a well-defined periapical radiolucency (PAI > 4)
• Teeth with previous root canal treatment performed at least 4 years prior
• Root canal fillings extending to at least the apical third without overfilling

Exclusion Criteria:

• Patients with symptoms such as pain, swelling, or sinus tract
• Patients with a history of smoking or alcohol use
• Teeth with open apices or root resorption
• Teeth with intraradicular posts
• Teeth with insufficient coronal tooth structure
• Teeth with perforation, instrument fracture, or overfilled canals
• Teeth with root curvature greater than 30 degrees
• Teeth with periodontal disease or probing depth >3 mm
• Cases not suitable for single-visit retreatment
• Patients who used analgesics within 12 hours prior to treatment
• Patients who used antibiotics within the last month
• Patients with cognitive impairment or psychological disorders

Due to the nature of the interventions, the operator could not be blinded. However, participants and the outcome assessor were blinded to group allocation. The statistician was also blinded during data analysis.