A reciprocating endodontic hand tool in which the toque applied to aninstrument such as a debriding file can be setat or below an endurance limit of the file below which failure of theinstrument will not occur. In preferred embodiments the tool canswitch between settings in which the torque applied to the instrument isbetween the endurance limit of the file and an elastic limit ofthe file, by setting forward and reverse angles of rotation within specifiedlimits. This reduces or eliminates opportunites for plasticdistortion, fatigue and breakage of the file during the canaldebriding/cleaning/shaping process in a root canal treatment orretreatment. In some embodiments the torque may be set to at or below adurability limit of the files below which failure of the instrumentwill not occur through repetitive strain over the course of a particular rootcanal treatment or retreatment.
