title: Flexibility and resistance to cyclic fatigue of endodontic instruments made with different nickel-titanium alloys: a comparative test.
abstract: OBJECTIVE
  A new manufacturing method aiming at to producing more flexible and resistant NiTi endodontic instruments has been recently developed (Hyflex, produced with CM wire). The purpose of the study was to determine whether this new manufacturing method produces NiTi instruments (Hyflex) of superior flexibility and/or superior resistance to cyclic fatigue, when compared with instruments produced by a traditional manufacturing process or thermally treated NiTi alloy (M-wire).
  
  
  METHODS
  Twelve .06 size 25 Hyflex instruments (Coltene, Allstatten, Switzerland), and twelve 06.25 Vortex instruments (Dentsply-Tulsa, OK, USA) and twelve 06.25 Endosequence instruments (Brasseler, Savannah, GA, USA) were initially evaluated for stiffness on bending, followed by a cyclic fatigue test. For the stiffness test test procedures strictly followed ISO 3630-1, and bending moment was measured when the instrument attained a 45 degrees bend. The cyclic fatigue test was performed in a customized artificial stainless steel canal (60° degree curvature with 5 mm radius). Instruments were rotated at 300 rpm until fracture. All data obtained were recorded and statistically analyzed using an ANOVA test.
  
  
  RESULTS
  Statistical analysis of data showed that bending moments were significantly greater (P < .05) for Vortex and EndoSequence instruments (mean values 59.06 g/cm and 48,98 g/cm respectively), compared to the Hyflex instruments (mean value 35.60 g/cm). For the cyclic fatigue test Hyflex and Vortex were significantly more resistant than EndoSequence instruments (P < .05).
  
  
  CONCLUSIONS
  Results of the present study demonstrate the ability of the new CM-wire manufacturing process to produce NiTi rotary instruments more flexible and more resistant to cyclic fatigue than instruments produced by a traditional manufacturing process or a thermally treated NiTi alloy (M-wire).
authors: Department of Oral and Maxillofacial Sciences, Sapienza University of Rome, Italy.
authors: Giancarlo
authors: G
authors: Pongione
authors: Giorgio
authors: G
authors: Pompa
authors: Valerio
authors: V
authors: Milana
authors: Stefano
authors: S
authors: Di Carlo
authors: Alessio
authors: A
authors: Giansiracusa
authors: Emanuele
authors: E
authors: Nicolini
authors: Francesca
authors: F
authors: De Angelis
keywords: NiTi alloy; cyclic fatigue test; resistance of endodontic instruments; rotary instruments
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