Assessment of the mechanical properties of ProTaper Next Nickel-titanium rotary files.

Introduction: The purpose of this study was to compare the torsional resistance, flexibility, and surface microhardness of ProTaper Next files (PTN) with Twisted Files (TF) and RaCe (RC).

Methods: A metal block with a cubical hole was used to evaluate the torsional resistance. Five millimeters of the tip of each file was securely held in place by filling the mold with a resin composite, and the files were driven clockwise at 300 rpm. The number of load applications before fracture was recorded for each file. A scanning electron microscope was used to characterize the topographic features of the fracture surfaces of the broken files. The files were tested for bending resistance by using cantilever-bending test. Vickers microhardness was measured on the cross section of instruments with 300-g load and 15-second dwell time. Torsional resistance data were analyzed by using the nonparametric Kruskal-Wallis and Mann-Whitney U tests. Bending resistance and microhardness data were analyzed by using analysis of variance and Tukey tests.

Results: PTN showed the highest torsional resistance and microhardness, followed by RC (P < .05). The fracture cross sections of all brands showed dimpling near the center of fracture surface. The ranking in the bending resistance values was as follows: RC > PTN > TF.

Conclusions: PTN improved its resistance to torsional stresses and wear compared with TF and RC. TF showed improved flexibility compared with other tested brands.