Structural Characterisation and Mechanical FE Analysis of Conventional and M-Wire Ni-Ti Alloys Used in Endodontic Rotary Instruments

Abstract

The purpose of this study is to understand how the M-Wire alloy conditions the mechanical flexibility of endodontic rotary files at body temperature.Two different rotary instruments, a Profile GT 20/.06 and a Profile GT Series X 20/.06, were selected due to their geometrical similarity and their different constituent alloy. GT series X files are made from M-Wire, a Ni-Ti alloy allegedly having higher flexibility at body temperature. Both files were analysed by X-Ray Diffraction and Differential Scanning Calorimetry to investigate phase transformations and the effects of working temperature on these different alloys. Mechanical behaviour was assessed by means of static bending and torsional Finite Element simulations, taking into account the nonlinear superelastic behaviour of Ni-Ti materials. It was found that GT files present austenitic phase at body temperature, whereas GT series X present R-phase at temperatures under 40°C with a potential for larger flexibility. For the same load conditions, simulations showed that the slight geometrical differences between the two files do not introduce great disagreement in the instruments' mechanical response. It was confirmed that M-Wire increases the instrument's flexibility, mainly due to the presence of R-phase at body temperature.

A study on the influence of Ni–Ti M-Wire in the flexural fatigue life of endodontic rotary files by using Finite Element Analysis

“…For example, the GT Series X (GTX) from Dentsply Tulsa Dental Specialties are manufactured using a heat-treated Ni-Ti wire called M-Wire [12]. Reported results suggest that GTX instruments are more resistant to flexural fatigue than similar GT instruments made with conventional Ni-Ti alloys 4 [13,15]. However, due to the files' small size (less than 1mm in diameter), it is very hard to measure with accuracy important mechanical properties that will contribute to fracture by fatigue, for instance the stress at a given location.…”

The Effect of Temperature on Cyclic Fatigue of Nickel-titanium Rotary Endodontic Instruments

“…N ickel-titanium (NiTi) endodontic rotary files possess superelasticity, which is of great benefit during instrumentation of curved endodontic canals (1). These instruments have an austenite phase at higher temperatures and, upon cooling or applying stresses, can transform into the martensite phase.…”

“…This phase transition allows for greater flexibility. The transition phase temperatures of files can differ depending on the alloys and heat treatments used for processing (1).…”

Determination of the rotary fatigue life of NiTi alloy wires

“…The part of the wire cross-section closer to the neutral line is still Austenitic, whereas; 2. The parts of the wire cross-section further away from the neutral line are going through the Austenite to B19' Martensite crystallographic transformation intermediate step characteristic from Ni-Ti superelastic alloys [15][16][17][18].…”