Surface analysis of nickel-titanium archwire used in vivo

Objectives. The surface quality of an archwire is a critical factor in the prevention of corrosion. This study was conducted to evaluate and assess the surface of as-received and used nickel-titanium archwires for evidence of corrosion, and to analyze possible corrosion products. Methods. Round 0.4 mm and square 0.4 mm x 0.55 mm nickel-titanium archwires from two manufacturers were subjected to elemental analysis, examined, and photographed in a scanning electron microscope with an EDAX unit. The used wires had been in service from 3 wk to 4 mon. There were no systematic differences in surface topography or composition between the as-received and used wires. Results. The examination revealed undulated surfaces with manufactural scratches and crevices. The surface quality within the same archwire varied slightly, with different smoothness in the anterior and posterior regions. No systematic discernible difference was found between used and as-received arch wires. The analyses of different areas on the used archwires revealed no differences in the metal composition. Significance. The surface defects found on the as-received wires were evidently not large enough to act as sites for corrosion attack.