Preoperative Video-Guided Breathing Exercise for Pain After Root Canal Treatment

The goal of this randomized controlled clinical trial is to evaluate whether a brief preoperative video-guided breathing exercise reduces postoperative pain in adults undergoing single-visit root canal treatment for symptomatic irreversible pulpitis. The main questions it aims to answer are: * Does a 2-minute video-guided breathing exercise reduce postoperative pain 24 hours after root canal treatment compared with a 2-minute period of passive rest? * Does the breathing exercise affect pain experienced during root canal treatment or postoperative pain at 6, 12, 48, and 72 hours? * Does the breathing exercise reduce the need for supplemental local anesthesia during treatment? * Does the breathing exercise reduce analgesic use during the first 72 hours after treatment? * Does the breathing exercise produce a greater immediate change in heart rate compared with passive rest? Participants will be randomly assigned to one of two groups before root canal treatment. In the video-guided breathing exercise group, participants will watch a standardized 2-minute video and follow a controlled breathing pattern consisting of inhaling through the nose for 4 seconds followed by exhaling for 6 seconds. This breathing cycle will be repeated throughout the video. In the passive rest group, participants will remain seated in the dental chair for 2 minutes without receiving any breathing or relaxation instructions and will be asked to breathe normally. All participants will then receive single-visit root canal treatment using the same standardized endodontic treatment protocol. Postoperative pain will be assessed at 6, 12, 24, 48, and 72 hours after treatment. Pain at 24 hours will be the primary outcome. Maximum pain experienced during treatment, supplemental anesthesia requirement, analgesic use during the first 72 hours, and change in heart rate immediately before and after the assigned preoperative intervention will also be evaluated.