The impact of composition, core metal mass and phase transformation behaviour on the dynamic cyclic fatigue of Ni-Ti files at different temperatures

Submitted: 21 February 2022
Accepted: 25 February 2022
Published: 31 May 2022
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Aim: To assess impact of elemental composition, core metal mass and phase transformation behaviour on the dynamic cyclic fatigue resistance of three Ni-Ti rotary files at room and body temperatures.

Methods: Twenty instruments of each system were tested for dynamic cyclic fatigue resistance in a simulated root canal with a 90˚ angle of curvature and a 5-mm radius of curvature at room and body temperature. The core metal mass at the fractured surface of each instrument was calculated by Image J software analysis of SEM images. The energy dispersive X-ray analysis was used to assess file composition. Scanning calorimetry was used to assess the structural phase state and the transformation temperature. One-way analysis of variance (ANOVA) was performed to determine any statistical difference amongst groups. For inter-group comparison, the unpaired t-test was used.

Results: HEDM showed significantly higher TtF and NCF values than AFBS and ZB-F6 instruments, at both temperatures tested. The mean core metal mass was smallest in HEDM followed by AFBS with no statistical difference between them, while ZB-F6 had the significantly largest metal core. EDX analysis showed that all the instruments were mainly composed by nickel and titanium. DSC analysis revealed that HEDM and AFBS exhibited a martensitic phase at body (37˚C) and room temperature (25˚C), whereas ZB-F6 revealed an austenitic phase at body temperature.

Conclusions: Dynamic cyclic fatigue resistance increased when the instruments had less cross-sectional metal mass, less Ni (wt%), a thermally treated surface, and a martensite phase at body temperature.

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Mohamed Salah Abdel Aziz Elwakeel, Endodontic department, Faculty of dentistry, Ain Shams university

Teaching Assistant, Department of Endodontics, Faculty of Dentistry, Egyptian russian university in Egypt.‎

Ahmed Abdel Rahman Hashem , Department of Endodontics, Faculty of Dentistry, Ain Shams University

1-Professor and head of Endodontics Department , Faculty of Dentistry, Ain Shams University in Egypt.‎
2-Director of Microscope Centre, Future University, Egypt.
3-Visiting Professor, Cleveland Dental Institute, USA
4-Secretary General, Egyptian Association of Endodontists
5-International member, American Association of Endodontists
6-Member, British Endodontic Society
7-Member, Scientific Advisory board, Journal of Endodontists
8-Private practice limited to Micro-Endodontics

Sarah Hossam Fahmy, Department of Endodontics, Faculty of Dentistry, Ain Shams University

1-Lecturer of Endodontics, Department of Endodontics, Faculty of Dentistry, Ain Shams University in Egypt.‎

Elwakeel, M. S. A. A., Hashem , A. A. R., Fahmy, S. H. ., Saber, S. M., & Plotino, G. (2022). The impact of composition, core metal mass and phase transformation behaviour on the dynamic cyclic fatigue of Ni-Ti files at different temperatures. Giornale Italiano Di Endodonzia, 36(1).


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