A novel model to evaluate the fatigue resistance of NiTi instruments: Rotational and axial movement at body temperature

Abstract

To develop a model to test cyclic fatigue resistance of TruNatomy instruments undergoing rotational and axial movement at body temperature. A total of 288 Prime and Medium instruments were subjected to cyclic fatigue testing in simulated canals (at 37°C) using a model with either rotational movement only or rotational and axial movement simultaneously. Two different sized canals and three different types of curvatures were tested for each instrument (30/0.04 and 30/0.06 for Prime; 38/0.04 and 40/0.06 for Medium). The number of cycles to failure (fatigue resistance) was recorded. Rotational and axial movement of instruments led to greater fatigue resistance compared with rotational movement alone. Apical curvatures led to greater fatigue resistance than curvatures in the coronal and middle third. The developed dynamic model at body temperature to evaluate fatigue resistance of instrument closer simulates clinical scenarios.

Evaluation of the Cyclic Fatigue Resistance of Tia Tornado Blue and Tia Tornado Gold in Curved Canals: In Vitro Study

“…This improvement allows the instrument to show different crystal configurations based on the applied temperature and strain (martensite and austenite) [37]. It provides a martensitic phase at a lower temperature, which gives the instrument the flexibility and the cyclic fatigue resistance required [13,21].…”

“…Two mechanisms of fracture have been identified include cyclic fatigue and torsional fatigue. Cyclic fatigue is defined by the tension/compression cycles at the point of maximum flexure, while torsional fatigue is determined when an instrument tip or another part of the instrument is locked in a canal while the shank continues to rotate, and the torque goes beyond the elastic limit of the metal of the endodontic instrument [12,13].…”

“…The changes in heat treatment are made by changing the transition temperatures of the NiTi instruments, hence improving their cyclic fatigue resistance and flexibility, in comparison to the conventional superelastic NiTi instruments [13]. At human body temperature, traditional NiTi instruments have a lower finish temperature for austenite transformation (16-31 • C).…”