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

Published:November 01, 2016DOI:


      • Cyclic fatigue resistance and torsional strength of Hyflex EDM, ProTaper Gold (PTG), and ProTaper Universal (PTU) instruments were evaluated.
      • Hyflex EDM files exhibited significantly higher resistance to cyclic fatigue than PTG and PTU files.
      • Hyflex EDM files demonstrated significantly lower torsional resistance than PTG instruments, despite their superior flexibility compared with other tested instruments.
      • Although PTG and PTU have similar cross-sectional design, PTG instruments presented higher cyclic fatigue and torsional resistance than PTU instruments.



      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.


      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).


      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.


      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.

      Key Words

      To read this article in full you will need to make a payment


        • Hülsmann M.
        • Schinkel I.
        Influence of several factors on the success or failure of removal of fractured instruments from the root canal.
        Dent Traumatol. 1999; 15: 252-258
        • Gutmann J.L.
        • Gao Y.
        Alteration in the inherent metallic and surface properties of nickel–titanium root canal instruments to enhance performance, durability and safety: a focused review.
        Int Endod J. 2012; 45: 113-128
        • Pirani C.
        • Iacono F.
        • Generali L.
        • et al.
        HyFlex EDM: superficial features, metallurgical analysis and fatigue resistance of innovative electro discharge machined NiTi rotary instruments.
        Int Endod J. 2016; 49: 483-493
        • Pedullà E.
        • Lo Savio F.
        • Boninelli S.
        • et al.
        Torsional and cyclic fatigue resistance of a new nickel-titanium instrument manufactured by electrical discharge machining.
        J Endod. 2016; 42: 156-159
        • ColteneEndo
        Brochure HyFlex EDM.
        2016 (Available at:) (Accessed April 2016)
        • Hieawy A.
        • Haapasalo M.
        • Zhou H.
        • et al.
        Phase transformation behavior and resistance to bending and cyclic fatigue of ProTaper Gold and ProTaper Universal instruments.
        J Endod. 2015; 41: 1134-1138
        • Ruddle C.J.
        The ProTaper technique.
        Endod Topics. 2005; 10: 187-190
        • Uygun A.D.
        • Kol E.
        • Topcu M.K.
        • et al.
        Variations in cyclic fatigue resistance among ProTaper Gold, ProTaper Next and ProTaper Universal instruments at different levels.
        Int Endod J. 2016; 49: 494-499
        • Elnaghy A.M.
        • Elsaka S.E.
        Mechanical properties of ProTaper Gold nickel-titanium rotary instruments.
        Int Endod J. 2015; (In press)
        • Larsen C.M.
        • Watanabe I.
        • Glickman G.N.
        • He J.
        Cyclic fatigue analysis of a new generation of nickel titanium rotary instruments.
        J Endod. 2009; 35: 401-403
        • Nguyen H.H.
        • Fong H.
        • Paranjpe A.
        • et al.
        Evaluation of the resistance to cyclic fatigue among ProTaper Next, ProTaper Universal, and Vortex Blue rotary instruments.
        J Endod. 2014; 40: 1190-1193
        • International Organization for Standardization ISO 3630-1
        Dental Root Canal Instruments: Part 1—Files, Reamers, Barbed Broaches, Rasps, Paste Carriers, Explorers and Cotton Broaches.
        International Organization for Standardization, Geneva, Switzerland1992
        • Cheung G.S.P.
        Instrument fracture: mechanisms, removal of fragments, and clinical outcomes.
        Endod Topics. 2007; 16: 1-26
        • Shen Y.
        • Cheung G.S.P.
        Methods and models to study nickel–titanium instruments.
        Endod Topics. 2013; 29: 18-41
        • Capar I.D.
        • Ertas H.
        • Arslan H.
        Comparison of cyclic fatigue resistance of nickel-titanium coronal flaring instruments.
        J Endod. 2014; 40: 1182-1185
        • Capar I.D.
        • Kaval M.E.
        • Ertas H.
        • Sen B.H.
        Comparison of the cyclic fatigue resistance of five different rotary path-finding instruments made of conventional nickel-titanium wire, M-wire and controlled memory wire.
        J Endod. 2015; 41: 535-538
        • Tobushi H.
        • Nakahara T.
        • Shimeno Y.
        • et al.
        Low-cycle fatigue of TiNi shape memory alloy and formulation of fatigue life.
        J Eng Mater Technol. 2000; 122: 186-191
        • Shen Y.
        • Qian W.
        • Abtin H.
        • et al.
        Effect of environment on fatigue failure of controlled memory wire nickel-titanium rotary instruments.
        J Endod. 2012; 38: 376-380
        • de Vasconcelos R.A.
        • Murphy S.
        • Carvalho C.A.
        • et al.
        Evidence for reduced fatigue resistance of contemporary rotary instruments exposed to body temperature.
        J Endod. 2016; 42: 782-787
        • Shen Y.
        • Riyahi A.M.
        • Campbell L.
        • et al.
        Effect of a combination of torsional and cyclic fatigue preloading on the fracture behavior of K3 and K3XF instruments.
        J Endod. 2015; 41: 526-530
        • Gambarini G.
        Cyclic fatigue of ProFile rotary instruments after prolonged clinical use.
        Int Endod J. 2001; 34: 386-389
        • Oh S.R.
        • Chang S.W.
        • Lee Y.
        • et al.
        A comparison of nickel-titanium rotary instruments manufactured using different methods and cross-sectional areas: ability to resist cyclic fatigue.
        Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2010; 109: 622-628
        • Hussne R.P.
        • Braga L.C.
        • Berbert F.L.
        • et al.
        Flexibility and torsional resistance of three nickel-titanium retreatment instrument systems.
        Int Endod J. 2011; 44: 731-738
        • Shen Y.
        • Hieawy A.
        • Huang X.
        • et al.
        Fatigue resistance of a 3-dimensional conforming nickel-titanium rotary instrument in double curvatures.
        J Endod. 2016; 42: 961-964
        • Shen Y.
        • Zhou H.M.
        • Zheng Y.F.
        • et al.
        Current challenges and concepts of the thermomechanical treatment of nickel-titanium instruments.
        J Endod. 2013; 39: 163-172
        • Campbell L.
        • Shen Y.
        • Zhou H.
        • Haapasalo M.
        Effect of fatigue on torsional failure of nickel-titanium controlled memory instruments.
        J Endod. 2014; 40: 562-565
        • Pereira É.S.
        • Viana A.C.
        • Buono V.T.
        • et al.
        Behavior of nickel-titanium instruments manufactured with different thermal treatments.
        J Endod. 2015; 41: 67-71
        • Pereira E.S.
        • Gomes R.O.
        • Leroy A.M.
        • et al.
        Mechanical behavior of M-wire and conventional NiTi wire used to manufacture rotary endodontic instruments.
        Dent Mater. 2013; 29: 318-324
        • Ninan E.
        • Berzins D.W.
        Torsion and bending properties of shape memory and superelastic nickel-titanium rotary instruments.
        J Endod. 2013; 39: 101-104