Objective To evaluate effect of root canal curvature and location of the fragment on the removal of broken file from root canal. Methods Sixty extracted mandibular premolars were divided equally into six groups according to location of fragment（2 mm or 8 mm below root canal orifice） and root canal curvature（20°, 30° or 40°）. Broken files were removed using ultrasonic tips combined with dental operating microscope. Number of successfully removed case and operating time were recorded. Pre- and post-operative digital radiographs were input into image analyzing software to calculate diameter variance of root canal at the level of tip of broken file. Results All the 6 groups of broken files were successfully removed with out perforation. Among same fragment location groups, diameter variance was increased in greater curvature groups and the difference was significant（P0.05）. Among same root canal curvature groups, the deeper the fragment, the longer operation time, difference being significant（P0.05）. Conclusion The more curvature of root canal, the more dentine removal amount at the level of broken file tip. Location of fragment has no effect on dentine removal amount. Safe straight-line access and adequate thickness of dentine are essential to removal of broken file from root canal.
