Research Article Structural Characterisation and Mechanical FE Analysis of Conventional and M-Wire Ni-Ti Alloys Used in Endodontic Rotary Instruments Diogo Montalvão, 1 Francisca Sena Alçada, 2 Francisco Manuel Braz Fernandes, 3 and Sancho de Vilaverde-Correia 3,4 1 School of Engineering and Technology, University of Hertfordshire, College Lane, Hatield, Hertfordshire AL10 9AB, UK 2 he Dental Implant and Gingival-Plastic Surgery Centre, 717 Christchurch Road, Bournemouth, Dorset BH7 6AF, UK 3 CENIMAT/I3N, Materials Science Department, Faculty of Science and Technology, New University of Lisbon, Campus of Caparica, 2829-516 Caparica, Portugal 4 Department of Endodontics, School of Dental Medicine, University of Pennsylvania, 3451 Walnut Street, Philadelphia, PA 19104, USA Correspondence should be addressed to Diogo Montalv˜ ao; d.montalvao@herts.ac.uk Received 22 August 2013; Accepted 27 October 2013; Published 20 January 2014 Academic Editors: F. Cleymand, E. Sahmetlioglu, and S. Wu Copyright © 2014 Diogo Montalv˜ ao et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. he purpose of this study is to understand how the M-Wire alloy conditions the mechanical lexibility of endodontic rotary iles at body temperature.Two diferent rotary instruments, a Proile GT 20/.06 and a Proile GT Series X 20/.06, were selected due to their geometrical similarity and their diferent constituent alloy. GT series X iles are made from M-Wire, a Ni-Ti alloy allegedly having higher lexibility at body temperature. Both iles were analysed by X-Ray Difraction and Diferential Scanning Calorimetry to investigate phase transformations and the efects of working temperature on these diferent 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 iles present austenitic phase at body temperature, whereas GT series X present R-phase at temperatures under 40 ∘ C with a potential for larger lexibility. For the same load conditions, simulations showed that the slight geometrical diferences between the two iles do not introduce great disagreement in the instruments’ mechanical response. It was conirmed that M-Wire increases the instrument’s lexibility, mainly due to the presence of R-phase at body temperature. 1. Introduction Stainless steel instruments are rigid and therefore unsuited for large apical enlargement in thin curved canals [1]. Ni-Ti alloys have superior properties in ductility, fatigue, recoverable strain, biocompatibility, and corrosion resistance [2]. Ni-Ti alloys’ lower Young’s modulus and superelastic behaviour are paramount for preparation of anatomically complex root canals, as lexibility preserves dental structure, limits apical transport, reduces the risk of iatrogenic mistakes, and ultimately allows for irrigants to low deeper in canals, towards the apical constriction [3, 4]. Also, some studies claim that there is now evidence [5] that Ni-Ti instruments yield better clinical prognosis in endodontics when compared to their stainless steel counterparts considered alone. However, Ni-Ti iles present a higher risk of unnoticed fracture inside canals [6], contrary to stainless steel iles that oten present visible signs of plastic deformation [7]. Unexpected premature ile fracture is of paramount concern as it might hinder clinical outcome. Some published studies show that Ni-Ti instruments fracture at a frequency ten times greater than their stainless steel counterparts [8, 9]. Furthermore, Ni-Ti fragments are up to seven times less likely to be removed from inside root canals, even by experienced endodontists [10]. his explains the current interest in the subject by several researchers [11–17]. Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 976459, 8 pages http://dx.doi.org/10.1155/2014/976459