Surface properties and metal ions leaching behaviors of nickel-titanium orthodontic archwires modified by oxidation

This study examined the metal ions released from nickel-titanium (TiNi) orthodontic archwires, which had been surface-modified by oxidation at various temperatures. The Ni ion was more easily leached from the TiNi orthodontic archwires than Ti ion, because the Ti atoms were readily to form passive TiO2 films on the surface. TiNi orthodontic archwires should be heat-treated at an appropriate temperature, such as 300 and 400 °C, to possess a smooth and intact TiO2 film on the surface, better corrosion-resistance properties, and fewer selectively leached Ni ions to ensure the long-term safety of the implantation. TiNi orthodontic archwires heat-treated at a higher temperature, such as 500 °C, may lead to poor corrosion-resistance properties and risk the increase of selectively leached Ni ions.