The relevance of operative torque and torsional resistance of nickel-titanium rotary instruments: A preliminary clinical investigation

Introduction: The aim of the present study is to evaluate the torsional resistance and the operative torque of two different files and to introduce the concept of 'torque range', that indicates the difference between torque at failure and operative torque. Materials and Methods: 20 ProTaper Next® (PTN) X1 and 20 EdgeFile® X7 17.04 were randomly divided into two equal groups (n = 10) and were subjected to the following two tests: operative torque recorded during root canal shaping of a single-rooted mandibular premolar and a torsional test performed at 300 rpm while the apical 3 mm of each file were firmly secured. The torque range was calculated from the difference between 'Operative torque' and 'torque at fracture.' A statistical t-test was performed to determinate the difference. Statistical significance was set at P < 0.05. Results: EdgeFile X7 instruments reached the working length significantly faster and with less torque generated (P < 0.05) compared to PTN. In torsional static resistance (torque at failure), the two files demonstrated no significant different values (P > 0.05). The range between the mean values of maximum torque at failure and operative torque, 'torque range,' was twice bigger for EdgeFile X7 instruments. Conclusions: The EdgeFile X7 has a wider 'torque range' when compared to PTN X1. This new concept could be a relevant innovation to match in vivo and in vitro studies and to obtain a more clinically relevant result.