The effect of rotational speed on force and torque during instrumentation of simulated root canals using ProTaper Next rotary files

Abstract

Introduction: Rotary nickel–titanium files are subjected to shear and flexural stresses during instrumentation. Increasing the rotational speed may reduce the shear stresses but can deteriorate the fatigue life of the file. This in vitro study aimed to address the influence of three rotational speeds 300, 500, and 700 RPM on the apical force and torque generated during instrumentation as well as on file fracture. Materials and Methods: A total of 48 simulated canals were divided into three groups: 300, 500, and 700 RPM (n = 16). Each canal was instrumented using a ProTaper Next XA orifice opener to prepare the coronal third and an X2 shaper to prepare the middle and apical thirds. A new set of files (XA and X2) was used to prepare four canals. A customized setup was used to evaluate the maximum apical force and torque corresponding to each third of the canal. The files were inspected for deformation or fracture using a stereomicroscope. Force and torque data were analyzed using analysis of variance and Post hoc Tukey test at 5% significance. Results: Five hundred and 700 RPM generated a significantly lower apical force and torque than 300 RPM at all canal thirds (P < 0.001). However, 700 RPM was superior to 500 RPM at the coronal third only (P < 0.001). No incidence of deformation or fracture was reported in any group. Conclusions: In resin artificial canals, increasing the rotational speed of the tested ProTaper Next files resulted in significantly less apical force and torque without increasing the incidence of fracture. Further studies involving natural teeth are required to validate these results using natural teeth.