Surface Characterizations and Corrosion Resistance of Nickel-titanium Orthodontic Archwires in Artificial Saliva of Various Degrees of Acidity

This study investigated the surface characterizations and corrosion resistance of as-received commercial nickel-titanium (NiTi) dental orthodontic archwires from different manufacturers using a cyclic potentiodynamic test in artificial saliva with various acidities. An atomic force microscope was used to evaluate the surface topography of the NiTi wires. The surface chemical analysis of the passive film on the NiTi wires was characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy. A scanning electron microscope, together with an energy-dispersive spectrometer, was used to analyze the surface characterizations of the NiTi wires before and after the corrosion tests. Two-way analysis of variance was used to analyze the corrosion-resistance parameters with the factors of wire manufacturer and solution pH. The results showed that the surface structure of the passive film on the tested NiTi wires were identical, containing mainly TiO2, with small amounts of NiO. A different surface topography was observed on the NiTi wires from various manufacturers. The corrosion tests showed that both the wire manufacturer and solution pH had a statistically significant influence on the corrosion potential, corrosion rate, passive current, breakdown potential, and crevice-corrosion susceptibility. The difference in the corrosion resistance among these NiTi dental orthodontic archwires did not correspond with the surface roughness and pre-existing defects.