Effect of preset torque setting on torque/force generation, shaping ability and surface changes of nickel titanium rotary instrument in different root canal curvature locations: An ex vivo study

The aim of this study was to evaluate how preset torque settings influence the torque, vertical force, and root canal-centering ability of ProGlider and ProTaper NEXT nickel-titanium rotary instruments in canals with different curvature locations. Based on microcomputed tomography, mesial roots of human mandibular molars (25 degrees-40 degrees curvature) were allocated to the apical curvature (apical 1-5 mm) or the middle curvature (apical 5-9 mm) groups, and mandibular incisors (curvature <5 degrees) to the straight canal group. Each group was subjected to automated instrumentation and torque/force measurement with the preset torque of 1, 2.5, or 5 N center dot cm. Canalcentering ratios were determined with micro-computed tomography. Instrument fracture occurred only in the 2.5 and 5 N center dot cm groups in curved canals. The preset torque setting and curvature location did not influence canal shaping ability.