Evaluation of the Cyclic Fatigue and Torsional Resistance of Novel Nickel-Titanium Rotary Files with Various Alloy Properties

Abstract

Introduction: The purpose of this study was to evaluate the cyclic fatigue and torsional resistance of Hyflex EDM, ProTaper Gold (PTG), and ProTaper Universal (PTU) instruments.

Methods: For the cyclic fatigue test, 10 instruments from each group were tested by using a stainless steel block with 1.5-mm diameter and 3-mm radius of 60° angle of curvature. The instruments were allowed to rotate by using a low-torque motor, and number of cycles from the beginning to the fracture was recorded. Torsional resistance of the instruments (n = 10) was evaluated according to ISO 3630-1. The rotational speed of the instruments was set in the clockwise direction at 2 rpm. The maximum torque and angular deflection until fracture of the instrument were recorded. The data were analyzed by using one-way analysis of variance followed by post hoc Tukey test (P = .05).

Results: HyFlex EDM instruments exhibited the highest cyclic fatigue resistance and were followed by PTG and PTU groups, respectively. The mean fragment length for PTU instruments was significantly shorter than that for Hyflex EDM and PTG instruments. PTG instruments demonstrated significantly higher torsional resistance than HyFlex EDM files (P = .025), and the distortion angle of the instruments ranged as follows: PTU < PTG < Hyflex EDM files.

Conclusions: Hyflex EDM files demonstrated significantly higher cyclic fatigue resistance. Although PTG and PTU have similar cross-sectional design, PTG instruments presented higher cyclic fatigue and torsional resistance than PTU instruments. The enhanced alloy properties of PTG might be considered as the main reason for those differences.

Keywords: Cyclic fatigue; Hyflex EDM; electrical discharge machining; torsional resistance.