Introduction: This study compared the effect of several final irrigation agitation techniques (sonic agitation, passive ultrasonic irrigation, and manual dynamic agitation [MDA]) in comparison with needle irrigation on postoperative pain in mandibular molar teeth with symptomatic irreversible pulpitis. Methods: One hundred sixty-eight patients with a single tooth diagnosed as symptomatic irreversible pulpitis were selected. Teeth were randomly assigned to 4 groups based on the final irrigation methods. In group 1 (needle irrigation), irrigation was conducted without agitation with a side-port needle; in group 2, sonic agitation was used; in group 3, passive ultrasonic irrigation was used; and in group 4, MDA was used. Teeth were then obturated with gutta-percha and a resin-based sealer using the cold lateral compaction technique. The presence of postoperative pain was assessed after 6, 24, 48, and 72 hours and 1 week. Results: At the 6- and 24-hour time intervals, group 4 patients reported more intense postoperative pain than those patients in groups 1, 2, and 3 (P <.05). There was no significant difference among the groups at the other time intervals (P >.05), and in all groups the intensity of postoperative pain decreased over time. Conclusions: MDA caused greater postoperative pain after endodontic therapy in mandibular molar teeth with symptomatic irreversible pulpitis compared with the other methods in the first 24 hours.