Mechanical Properties of Orifice Preflaring Nickel-titanium Rotary Instrument Heat Treated Using T-Wire Technology

Abstract

Introduction: This study examined whether the use of T-Wire heat treatment enhanced the resistance to torsional force, cyclic fatigue, and bending stiffness of orifice preflaring nickel-titanium instruments.

Methods: Ninety heat-treated OneFlare (OFT; Micro-Mega, Besançon, France) and conventional OneFlare (OFC, Micro-Mega) nickel-titanium files of size #25/.09 with identical geometries were selected (n = 15 per group for each test). Torsional resistance was evaluated through the measurement of ultimate torsional strength, distortion angle, and toughness during rotational loading. Cyclic fatigue resistance was evaluated through measurement of the number of cycles to failure for each instrument. Stiffness was evaluated by observation of the bending moment on attaining a 45° bend. Independent t tests were performed for statistical analysis. After torsional and cyclic fatigue tests, all fractured fragments were examined under a field emission scanning electron microscope to observe characteristics of the fractured surfaces.

Results: OFT showed better cyclic fatigue resistance and lower bending stiffness than OFC (P < .05); however, OFT and OFC did not differ significantly in terms of torsional resistance. The fractured cross-sectional surfaces had characteristics typical of cyclic fatigue and torsional fractures.

Conclusions: The OFT instruments made using T-Wire heat treatment had better cyclic fatigue resistance and lower bending stiffness with no decline in torsional strength.

Keywords: Bending stiffness; OneFlare; T-Wire heat treatment; cyclic fatigue; nickel-titanium rotary file; preflaring; torsional resistance.