In Vitro Assessment of Nickel Ion Release from Orthodontic Wires

Abstract

Most of orthodontic alloys contain nickel. The consumption of acidic drinks may have an impact on these alloys in particular with respect to corrosion resistance. The corrosion is accompanied by nickel ion release that can generate hypersensitivity reactions. This study will quantify the release of nickel ions from orthodontic wires of stainless steel and nickel-titanium submitted to a bending constraint after a static immersion in acidified medium. Wire segments from Nickel-Titanium and stainless steel of which some are submitted to a bending constraint are immersed in acid media and then immersion solutions are analyzed using the inductive coupling plasma mass spectrometer (ICP-MS) with a detection threshold of 0.5ppb (μg/L). Nickel ions were detected in all analyzed samples. The results range from 2.4ppb to 9404ppb. Even with constraint, the release of nickel would be well below the level of daily food intake. The corrosive behavior depends on the properties of material, the manufacturing process, the environment, the pH values and the constraints. The surface condition is an important factor for corrosion. More the surface is rougher and the more likely it is to be attacked by corrosion especially by injection corrosion. The manufacturers should take this issue into account.