Abstract EN:

The first part of this work exposes a bibliographical synthesis about properties of memory-shape alloys and the characteristics of the small electric motors. The second part is experimental. We compared the resistance of instruments characterized by different profiles. We measured the differences induced by profile and pitch length on stresses generated by endodontic instrument used in continuous rotation. Then we try to evaluate the conditions of disengaging of different electric motors and contra-angles. We finally use, with a torque control motor, a file with the tip maintained in a screw-locking device. These studies show the role of instrument profile. Regarding the safe use of files, it appears more effective to work on the instruments design than to use controlled torque motor which are far away from manufacturers’ specifications. The use of badly calibrated disengaging or coupled to reversed rotation is completely ineffective.