Design and setting. Prospective, randomized, parallel-group, blinded clinical trial conducted at a university dental hospital (Istanbul, Turkey). All treatments were completed in a single visit by an experienced endodontist using local anaesthesia and rubber-dam isolation.
Participants. Adults (18 years or older) with single-rooted, single-canal teeth diagnosed with asymptomatic apical periodontitis on periapical radiographs were eligible. Exclusion criteria included symptomatic apical periodontitis or acute abscess, previous root-canal treatment of the study tooth, systemic conditions interfering with pain assessment or requiring antibiotic prophylaxis, pregnancy or lactation, known allergy to study materials, and use of analgesics or anti-inflammatory drugs within 12 hours before treatment. One patient contributed one tooth.
Randomization, allocation concealment, and masking. Participants were randomized 1:1 to OCT or CHX using computer-generated permuted blocks with stratification by baseline pain (NRS \<= 3 vs \> 3). Allocation was concealed with sequentially numbered, opaque, sealed envelopes. Irrigants were prepared by a third party in identical opaque syringes labelled A/B. Participants, the care provider (operator), and the outcomes assessor were blinded until database lock.
Interventions. Working length was established with an electronic apex locator and confirmed radiographically when needed. Root canals were prepared with nickel-titanium rotary instruments to size 40/0.04. During shaping, 5.25 percent sodium hypochlorite was used (approximately 2 mL after each instrument change). The smear layer was removed with 17 percent EDTA (about 10 mL) activated with a sonic device, followed by saline. For the final irrigation, the allocated solution was delivered and sonically activated using the same protocol in both groups: OCT 0.1 percent or CHX 2 percent, activated in three 20-second cycles with the solution refreshed with 2 mL between cycles (approximate total 6 mL). A side-vented needle was placed short of the working length. Root-canal obturation was completed in the same session using gutta-percha and an epoxy resin-based sealer with cold lateral compaction. Access cavities were restored with a resin composite. Rescue analgesics were permitted as needed and recorded by patients.
Outcomes. Primary outcome: patient-reported pain on the 0-10 NRS at 48 hours after treatment. Secondary outcomes: NRS pain at 6, 12, and 24 hours; total rescue analgesic consumption from 0 to 48 hours; and unplanned urgent care or adverse events within 48 hours.
Sample size and analysis plan. The a priori sample-size calculation assumed a between-group difference of 1.0 NRS unit (SD 2.0), alpha 0.05, and power 0.80, yielding 100 participants; allowing for attrition, the target was 120. Analyses compared groups at 48 hours and evaluated pain trajectories over time using mixed-effects methods with fixed effects for group and time and a random intercept for participant. Two-sided p \< 0.05 was considered statistically significant.
Oversight. The protocol was approved by the Bezmialem Vakif University Clinical Research Ethics Committee (approval E.99606). The trial was conducted in accordance with the Declaration of Helsinki.
