The purpose of the study was to reveal the effects of a new electropolishing process carried out under a constant magnetic field, termed as magnetoelectropolishing (MEP). In this work we investigated Nitinol rotary endodontic instruments by surface and morphology change after MEP. The MEP process greatly affects both surface also mechanical properties like the bending and fatigue resistance.
The investigation covered surface interferometry measurements, X-ray Photoelectron Spectroscopy (XPS) studies, and Scanning Electron Microscopy (SEM) with EDAX studies referred to two groups of endodontic instruments: ready-to-use or as-received (AR) files, and magnetoelectropolished (MEP) instruments, in comparison with the instruments surface after a conventional electropolishing (EP). The treated surfaces of NiTi endodontic files were studied by interferometric method in view of getting multiple surface characteristics, together with digital data concerning the arithmetic mean height Sa and the maximum height of scale limited surface Sz.
The investigation results obtained have indicated a considerable improvement of MEP surface in comparison with both AR and EP surfaces. Such a surface after MEP reveals several positive features, decreased roughness, elimination of metallic state (here Ni and Ti elements) in the surface film, much enriched with titanium oxides and diminished nickel oxides. The study results show that the contents of Ni compounds is higher after EP (18.3%) than after MEP (10.2%), whereas the contents of Ti compounds is higher after MEP (83.4%) than after EP (76.6%). The total Ti/Ni ratio indicates almost double surpass of titanium over nickel in the surface film after MEP in comparison with the total amount of that ratio after EP.
The qualitative investigation of fatigue tests have indicated much better performance of NiTi endodontic file samples after MEP than those related to AR and/or after EP. We have proved that the magnetoelectropolishing process may further modify surface. The following studies are to be directed onto performance and specific mechanical properties of the endodontic files at work.