Rationale for the use of low-torque endodontic motors in root canal instrumentation

Fracture of nickel-titanium rotary files is an iatrogenic error which can s eriously jeopardize root canal therapy. If a high-torque motor is used, the instrument-specific limit-torque (fracture limit) is often exceeded, thus increasing the risk of intracanal failure. A possible solution to this prob lem is to use a low-torque endodontic motor which operates below these valu es. If the torque is set just below the limit of elasticity for each instru ment, the risk of fracture is likely to be markedly reduced. The purpose of this paper was to discuss mechanical properties of NiTi rotary instruments , the rationale for selecting low torque values, and to use clinically a ne w endodontic motor (step-motor) which operates below the limit of elasticit y of each rotary file. The step-motor was found to be helpful in reducing t he risk of instrument fracture. Irreversible material damage (plastic defor mation) and instrument fracture were rarely seen. Low-torque instrumentatio n also increased tactile sense and, consequently, mental awareness of rotar y instrumentation.