1. Microscopic Features of Fractured Fragment of Nickel-Titanium Endodontic Instruments by Two Different Modes of Torsional Loading
- Author
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Sang Won Kwak, Ibrahim H. Abu-Tahun, Hyeon-Cheol Kim, and Jung-Hong Ha
- Subjects
Materials science ,lcsh:QH201-278.5 ,Article Subject ,Scanning electron microscope ,030206 dentistry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Atomic and Molecular Physics, and Optics ,Abrasion (geology) ,03 medical and health sciences ,Torsional load ,0302 clinical medicine ,Nickel titanium ,Dimple ,Fracture (geology) ,Composite material ,0210 nano-technology ,lcsh:Microscopy ,Instrumentation ,Research Article - Abstract
This study compared the microscopic features of the fractured endodontic nickel-titanium (NiTi) rotary instruments by two different torsional loadings: repetitive torsional loading (RTL) and single torsional loading (STL) based on the International Organization for Standardization (ISO). ProTaper Next, HyFlex EDM, and V-Taper 2 were compared in this study. In the STL method, the torsional load was applied after fixing the 3 mm tip of the file, by continuous clockwise rotation (2 rpm) until fracture. In the RTL method, a preset rotational loading (0.5 N·cm) was applied and the clockwise loading to the preset torque and counterclockwise unloading to original position were repeated at 50 rpm until the file fractured. Fractured fragments by two methods were compared under a scanning electron microscope (SEM) to examine the topographic features of the fractured surfaces and longitudinal aspects. SEM examinations showed significantly different features according to the loading methods. Specimens from the RTL method showed ruptured aspects on cross sections, with multiple areas of initiated cracks while the STL method showed the typical features of torsional failure, such as circular abrasion marks and fatigue dimples. This study suggested a new repetitive torsional loading method which is much more clinically relevant and may result in a different fracture feature from STL method.
- Published
- 2018
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