Endodontic tool and method

Abstract

A reciprocating endodontic hand tool in which the torque applied to an instrument such as a debriding file can be set at or below an endurance limit of the file below which failure of the instrument will not occur. In preferred embodiments the tool can switch between settings in which the torque applied to the instrument is between the endurance limit of the file and an elastic limit of the file, by setting forward and reverse angles of rotation within specified limits. This reduces or eliminates opportunites for plastic distortion, fatigue and breakage of the file during the canal debriding/cleaning/shaping process in a root canal treatment or retreatment. In some embodiments the torque may be set to at or below a durability limit of the file below which failure of the instrument will not occur through repetitive strain over the course of a particular root canal treatment or retreatment.

1 . A hand-held tool for rotating an endodontic instrument for preparing a root canal for filling in a root canal treatment or retreatment, the instrument having an elastic limit above which permanent deformation of the instrument will occur through repetitive strain, the tool comprising:
 an instrument holder,   a motor for applying a torque to the instrument holder and rotating the instrument holder through a selected arc of rotation alternately in each of forward and reverse directions, and   a motor controller limiting at least the forward arc of rotation to an angle not more than an endurance limit of the instrument of about 10 degrees in the event of substantial resistance against rotation of the instrument,   whereby the instrument can cut the canal, remove material and advance in the canal.   
     
     
         2 . The hand-held tool of  claim 1 , wherein the reverse rotational arc of motion is set at or below about 10 degrees in the event of substantial resistance against rotation of the instrument. 
     
     
         3 . The hand-held tool of  claim 1 , wherein the motor controller is selectively switchable to conduct the limiting. 
     
     
         4 . The hand-held tool of  claim 1 , wherein the motor controller automatically conducts the limiting. 
     
     
         5 . The hand-held tool of  claim 1 , wherein the motor controller is selectively switchable to a setting limiting at least the forward arc of rotation to an angle at or below the elastic limit of the instrument in the event of no substantial resistance against rotation of the instrument. 
     
     
         6 . The hand-held tool of  claim 5 , comprising:
 a torque sensor associated with the motor controller sensing for substantial resistance against rotation of the instrument.   
     
     
         7 . The hand-held tool of  claim 6 , wherein the hand-held tool automatically switches to a setting limiting the arcs of rotation of the instrument or the torque applied to the instrument, or both, to an angle at or below the endurance limit of the instrument in the event that the torque sensor senses a substantial resistance against rotation of the instrument. 
     
     
         8 . The hand-held tool of  claim 5 , wherein a forward arc of rotation of the instrument is greater than a reverse arc of rotation of the instrument.