Failure of ProFile instruments used with air, high torque control, and low torque control motors.

OBJECTIVE The purpose of this study was to evaluate the influence of 350-rpm rotational speed on the failure incidence of ProFile nickel-titanium rotary instruments (PRI) when used by an experienced operator in conjunction with different motors. STUDY DESIGN Extracted human mandibular and maxillary first and second molars demonstrating curvatures greater than 25 degrees were used. PRI sizes 40 to 15 and with 0.06 taper were used in crown-down fashion at 350 rpm. In groups 1 through 4, air, high torque control, low torque control, and very low torque control motors were used, respectively. Each group included 30 canals. One set of PRI was used for each canal. Before each use the PRI set was sterilized by steam autoclave. The canals were enlarged until a size 25 PRI reached the working length. A 2.5 x magnification was used to check for instrument deformation after each passage. The number of deformed and separated instruments was recorded for the various experimental groups. RESULTS Instrument deformation and separation did not occur in any of the 4 groups. CONCLUSIONS The results suggested that the use of PRI in conjunction with the different motors by an experienced operator in a crown-down manner at 350 rpm is safe.