The aim of this study is to evaluate the effect of intracanal cryotreated (2-3°C) 2.5% sodium hypochlorite and Saline used throughout the procedure, compared with a room-temperature irrigation protocol with a final cryotreated saline flush or an entirely room temperature irrigation protocol, on postoperative pain in patients with symptomatic irreversible pulpitis and symptomatic apical periodontitis in mandibular molars.