This randomized controlled trial aims to evaluate the effect of two different concentrations of sodium hypochlorite (2.5% and 5.25%) on post-operative pain following single-visit root canal treatment. A total of 116 participants requiring primary endodontic treatment will be randomly allocated into two groups according to irrigant concentration. Post-operative pain will be assessed using a 100-mm Visual Analog Scale at 6, 12, 24, and 48 hours after treatment. The study seeks to determine the concentration that provides optimal disinfection with minimal patient discomfort.