Abstract
The electrochemical characteristics of polytetrafluoroethylene (PTFE) coating produced on NiTi orthodontic wires were investigated. Electrochemical impedance spectroscopy (EIS) and linear potentiodynamic polarization (LPP) techniques in the conventional three-electrode configuration was employed to test the PTFE-coated NiTi wire during their exposure to artificial saliva. For comparative purpose the same electrochemical measurements were performed on uncoated NiTi wire. In addition, scanning electron microscopy (SEM) was employed to observe the surface morphology of both uncoated and PTFE-coated NiTi wires after LPP in artificial saliva. It was found that the PTFE-coated NiTi wire had a lower corrosion rate (corrosion and passive current density), about one order of magnitude lower than the uncoated NiTi substrates. The NiTi substrate was actually passive in these experimental conditions. The EIS interpretation was performed in two-layer model of the coated sample. The corrosion mechanism for the PTFE-coated NiTi wires arises from electrolyte penetration in the pore of the PTFE deposits. Keywords: PTFE-coated NiTi wire, artificial saliva, EIS, LPP, SEM