Corrosion Analysis of Orthodontic Wires: An Interaction Study of Wire Type, pH and Immersion Time

Variety of metal alloy wires are used in modern orthodontic treatment, such as, Stainless Steel (SS), cobalt-chromium, NickelTitanium (NiTi), Beta-Titanium (TMA), etc. These metal alloy wires are subjected to biodegradation in oral environments leading to corrosion. Although the risk is low, corrosion products such as nickel and chromium may cause sensitivities or allergic reactions during orthodontic treatment [1-5]. Other consequences may involve discoloration or roughening of surface leading to friction between the bracket and the arch wire [1,2]. Several intrinsic and environmental factors influence the corrosion reactions of orthodontic wires such as, types of alloys, surface roughness, surface coating, electrolyte, pH value, aging, immersion time and temperature [1,3,4,6-12]. Orthodontic appliances rely on the formation of a passive surface oxide film to resist corrosion. The addition of nickel and chromium in stainless steel alloy imparts corrosion resistance. The chromium in the stainless-steel forms a protective, passivating oxide layer (Cr2O3) that provides a barrier to oxygen diffusion and other corrosive environments [2]. The Australian wires are special type of high tensile stainless-steel wire, with rougher surface than other stainless steel [13,14]. The corrosion resistance of nickel-titanium wire is due to the large amount of titanium in its compositions with passivation surface film of several oxides (TiO, TiO2, Ti2O5) [2]. The beta-titanium alloy wire has excellent corrosion resistance and biocompatibility which is due to the presence of titanium oxide (TiO2) [2,15,16].