title: Effect of alloy type on the life-time of torsion-preloaded nickel-titanium endodontic instruments.
abstract: This study was aimed to evaluate the effect of torsional preloads on the cyclic fatigue life of nickel-titanium (NiTi) instruments with different history of heat treatments by manufacturers. WaveOne (Primary) made of M-wire, K3XF (#30/0.06) of R-phase, and ProTaper (F2) of conventional NiTi alloy was used. Each file was preloaded at four conditions (nil, 25, 50, and 75% of their mean ultimate torsional strength) before fatigue testing. The torsional preloads 10-, 30-, or 50-times were applied by securing 5 mm of the file tip, rotating it until the preset torque was attained before returning to the origin. Then, the number of cycles to failure (NCF) was evaluated by rotational bending in a simulated canal. Data were analyzed using multiple linear regression analysis and two-way ANOVA. Fractured instruments were examined under scanning electron microscope (SEM). SEM showed that most WaveOne after 75% preloading, regardless of repetitions, showed some longitudinal cracks parallel to the long axis of the file, which were rare for K3XF. Regression analysis revealed that the brand of instrument was the most critical factor. At up to 75% preloading, ProTaper and K3XF did not show any significant decline in NCF. For 30-repetition groups of WaveOne, the 50 and 25% torsion preloaded groups showed a significantly higher NCF than the 0 and 75% groups. Within the limitations of this study, the alloy type of NiTi instrument have a significant effect on the phenomenon that a certain amount of torsional preload may improve the cyclic fatigue resistance of NiTi rotary instruments.
authors: Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu, Korea.
authors: Jung-Hong
authors: JH
authors: Ha
authors: Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu, Korea.
authors: Sung Kyo
authors: SK
authors: Kim
authors: Area of Endodontics, Faculty of Dentistry, University of Hong Kong, Hong Kong SAR, China.
authors: Gary Shun-Pan
authors: GS
authors: Cheung
authors: Faculty of Health Science, Daegu Haany University, Gyeongsan, Korea.
authors: Seong Hwa
authors: SH
authors: Jeong
authors: Department of Oral Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu, Korea.
authors: Yong Chul
authors: YC
authors: Bae
authors: Department of Conservative Dentistry, School of Dentistry, Pusan National University, Dental Research Institute, Yangsan, Korea.
authors: Hyeon-Cheol
authors: HC
authors: Kim
mesh_terms: D000497:Alloys / Q000737:chemistry*; D003786:Dental Pulp Cavity; D004708:Endodontics / Q000295:instrumentation*; D004864:Equipment and Supplies; D006801:Humans; D008137:Longitudinal Studies; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008962:Models, Theoretical; D009532:Nickel; D018915:Root Canal Preparation / Q000379:methods; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium; D054159:Torsion, Mechanical
chemical_list: D000497:Alloys; D009532:Nickel; D014025:Titanium
keywords: NiTi rotary file; cross-section; cyclic fatigue; thermal treatment; torsional preload