IRCT20250923067345N1 IRCT 2025-10-01 Islamic Azad University Evaluation of the Effect of Low-Level Laser Therapy on Reducing Pain After Root Canal Treatment Evaluation and Comparison of the Effects of Low-Level Laser Therapy at 810 nm and 660 nm in Reducing Postoperative Pain Following Root Canal Treatment of Maxillary and Mandibular Premolars and Molars with Irreversible Pulpitis Accompanied by Apical Periodontitis 2025-09-27 anticipated 28 Complete https://irct.ir/trial/86358 interventional Randomization: Not randomized, Blinding: Double blinded, Placebo: Not used, Assignment: Parallel, Purpose: Treatment, Other design features: In our study, the effect of two different laser wavelengths on postoperative pain after root canal treatment are evaluated, and no control group is included, Blinding description: Patients: In our study, patients are unaware of which type of laser they receive (810 nm or 660 nm). Data Analyst: The statistician does not know which group received which wavelength and only evaluates the pain levels at different time intervals. N/A Postoperative pain after root canal treatment in posterior teeth with irreversible pulpitis accompanied by symptomatic apical periodontitis in the maxilla and mandible.. Intervention 1: Intervention Group 1: Laser irradiation at a wavelength of 660 nm with a power of 100 W and an energy of 4 J for 40 seconds over an area of 1 cm² at the apex of the treated tooth, applied to both the buccal and lingual/palatal surfaces. Intervention 2: Intervention Group 2: Laser irradiation at a wavelength of 810 nm with a power of 100 W and an energy of 4 J for 40 seconds over an area of 1 cm² at the apex of the endodontically treated tooth, applied to both the buccal and lingual/palatal surfaces. Undecided - It is not yet known if there will be a plan to make this available Justification or reason for indecision in sharing IPD is No further information is available. I have no objection to the publication of the data.