Introduction: Postoperative pain is one of the most critical issues in our daily practice. , postoperative pain control is essential for patient satisfaction and comfort. When primary root canal treatment fails, root canal retreatment aims to heal apical periodontitis.

Aim of study: To compare between postoperative pain (POS) after endodontic retreatment using NI-TI rotary files Mtwo R alone and in conjunction with XP endo finisher .

Materials and Methods: This research is a randomized clinical trial conducted in a parallel design on 50 patients needing retreatment. They will be divided into two groups, group 1 retreatment with Mtwo R, group 2 retreatment with Mtwo R followed by Xp - Endo finisher. Postoperative pain levels will be evaluated at 24 hours, 48 hours, 72 hours, and 7 days following the removal of the obturation mat erial. The assessment of pain will be done through clinical examination, The Defense and veterans pain rating scale (DVPRS) and by the intake of pain killer

Inclusion Criteria:

• Teeth with mature apices.
• Patients with no systemic diseases.
• No analgesic, anti-inflammatory, or antibiotic intake during 7 days before treatment.
• Teeth showing failure of initial root canal treatment and radiograph evidence of periapical bone destruction

Exclusion Criteria:

• Multi rooted teeth.
• Teeth with open apices.
• Teeth with cracks, calcification, root caries, fractures, external or internal resorption.
• Allergies to local anesthetic agents.
• Presence of severe pain and/or acute apical abscesses