Determination of corrosion rate of orthodontic wires based on nickel-titanium alloy in artificial saliva

The goal of this study was to determine corrosion behavior of three orthodontic wires based on nickel-titanium alloy (NiTi) in artificial saliva at temperature of 37 degrees C as function of immersion time. Following orthodontic wires were used: uncoated (NiTi), rhodium coated (Rh NiTi) and nitrified (N NiTi) orthodontic wires. Corrosion of investigated orthodontic wires were monitored by measuring of Ni2+ and Ti4+ ions released in artificial saliva by inductively coupled plasma-optical emission spectroscopy (ICP-OES) after 3, 7, 14, 21 and 28 days of immersion. Obtained results indicate that corrosion reaction of the NiTi wires in artificial saliva follows the parabolic rate law. According to the obtained values of parabolic corrosion rate constants, corrosion susceptibility of orthodontic wires decreases in the following order: Rh NiTi wire (K-p=2.48 g(2)/cm(4) h) > NiTi wire (K-p=1.6x10(-3) g(2)/cm(4) h) > N NiTi wire (K-p=6.0x10(-4) g(2)/cm(4) h). These results indicate that in comparison with uncoated NiTi wire, rhodium coating significantly increases corrosion susceptibility, while nitrification effectively suppresses the release of Ni2+ and Ti4+ ions.