This clinical study aims to evaluate the effect of different root canal irrigation techniques on postoperative pain levels and periapical healing in premolar and molar teeth diagnosed with apical periodontitis (Periapical Index (PAI) score 4-5). A total of 162 patients are randomly assigned to one of three groups: (1) sonic irrigation activation using EDDY, (2) ultrasonic irrigation activation using VDW Ultra, and (3) conventional syringe irrigation as the control. Postoperative pain will be recorded using the Visual Analog Scale (VAS) and Visual Analog Scale (VRS) at multiple time points up to one month. Periapical healing will be assessed using periapical imaging performed with the parallel technique one year after treatment. The study aims to determine whether enhanced irrigation techniques provide superior clinical outcomes compared to traditional methods.

Root canal treatment aims to eliminate microorganisms and their byproducts from the complex root canal system to allow periapical tissue healing. Due to the anatomical complexity of root canals-such as isthmuses, apical deltas, and lateral canals-mechanical preparation alone is often insufficient. Therefore, chemical irrigation plays a vital role in successful disinfection.

This randomized clinical trial investigates the influence of three different irrigation protocols on postoperative pain and periapical healing in permanent premolar and molar teeth with radiographically evident apical periodontitis (Periapical Index (PAI) score 4-5).

The study includes three experimental groups :

Group 1 (Sonic activation): Irrigation solution is activated using the EDDY sonic tip.

Group 2 (Ultrasonic activation): Irrigation is activated using VDW Ultra ultrasonic tips.

Group 3 (Control): Conventional needle irrigation is performed without activation.

All treatments will be performed under rubber dam isolation and local anesthesia, using a standardized instrumentation protocol with ProTaper Next rotary files. Between each file change, the root canal will be irrigated with 5 ml of 3% sodium hypochlorite (NaOCl). The final irrigation protocol will be applied according to the assigned group. All endodontic procedures will be completed in a single session.

Postoperative pain levels will be assessed using both the Visual Analog Scale (VAS) and Visual Analog Scale (VRS) scales at 6, 12, 18, 24, 48, and 72 hours, as well as on day 7 and at 1 month. Patients will be asked to record analgesic consumption (400 mg ibuprofen as needed) and will submit pain diaries.

One year after treatment, periapical healing will be evaluated using periapical radiography (parallel technique) by two blinded observers.

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Inclusion Criteria:

• Age between 18 and 60 years
• Premolar and molar teeth with radiographically confirmed periapical lesions classified as Periapical Index (PAI) scores of 4 or 5 will be included in the analysis
• Systemically healthy individuals
• To be able to read and sign the informed consent form
• Physical and mental fitness to undergo treatment
• Willingness to attend all follow-up sessions

Exclusion Criteria:

• Patients with systemic diseases classified as ASA III or higher
• Presence of severe periodontal disease (probing depth >4 mm)
• Use of analgesics within the last 12 hours or antibiotics within the past month before the treatment

All collected individual participant data (IPD), including all IPD that underlie the results reported in the publication

Data will be shared starting 6 months after publication.

Qualified researchers may request access to all de-identified individual participant data (IPD) and study protocols. Access will be granted upon reasonable request by contacting the corresponding author via email and after signing a data sharing agreement