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Abstract
In recent decade Nitinol have become the main material for production of endodontic rotary files where fatigue resistance, elasticity and resistance to torsional fracture are highly desirable. But in spite of this mechanical attributes fracture of NiTi rotary files during clinical use occur. The corrosion and fatigue resistance of endodontic files are influence by many interconnected factors namely: presence of hydrogen in starting material, surface quality, hydrogen introduce to files during finishing processes as eching, electropolishing, hydrogen introduce during sterilization and disinfect ion. To overcome these obstacles and improve corrosion and fatigue resistance many processes have been proposed including: electropolishing, cryogenic treatment, nitriding (etc). In present work we have evaluated “magnetoelectropolishing” (electropolishing under influence of uniform magnetic field) as alternative process for improvement of corrosion and fatigue resistance of Nitinol endodontic rotary files and compared this new technique with conventional electropolishing process. To evaluate influence of “magnetoelectro-
polishing” process we used electrochemical tests: (Open Circuit Potential (OPC), Polarization Curves (PC), Electrochemical Impedance Spectroscopy (EIS) and mechanical bending test (number of bending cycles required to fracture). To evaluate surface condition and fracture morphology scanning electron microscope (SEM) was used. The study has shown essential improvement in corrosion resistance of “magnetoelectropolished” files, which most probably arise from enrichment of passive layer in Ti by selectively dissolved Ni. The number of bending cycles necessary to break files was increased of about 40% when compared to conventionally electropolished files.
The main factor, which influence improved fracture resistance of “magnetoelectro-
polished” files were created by remarkable ability of this new process to degas of hydrogen from the files.