A reciprocating endodontic hand tool in which the torque applied to aninstrument such asa debriding file can be set at or below an endurance limit of the file belowwhich failureof the instrument will not occur. In preferred embodiments the tool can switchbetweensettings in which the torque applied to the instrument is between theendurance limit ofthe file and an elastic limit of the file, by setting forward and reverseangles of rotationwithin specified limits. This reduces or eliminates opportunites for plasticdistortion,fatigue and breakage of the file during the canal debriding/cleaning/shapingprocess in aroot canal treatment or retreatment. In some embodiments the torque may be setto at orbelow a durability limit of the file below which failure of the instrumentwill not occurthrough repetitive strain over the course of a particular root canal treatmentorretreatment.
