Relationship between electrochemical corrosion and the tribologic properties of orthodontic alloys

The aim of this study was to investigate the electrochemical properties of orthodontic alloys (SS, CuNiTi and TMA) and the impact of corrosion on their friction coefficient. Twelve pairs of 5-cm long 017 × .025 rectangular wires (SS/SS, CuNiTi/SS, TMA/SS) were formed and SEM observations and friction tests were conducted on the surface of each pair of wires. Then, each type of alloy was dipped in artificial saliva during different immersion times (24 h, 48 h, 72 h and 1 week). Following the electrochemical tests, the samples were recovered for a second series of SEM observations and a second friction test. After 24 h of immersion, we observed corrosive attacks on the surface of the alloys and a reduction of the friction coefficients. After 1 week, we observed surface passivation and an increased friction coefficient which attained values identical to those prior to immersion. One can conclude that, at the onset of corrosion, the friction coefficient decreases but that this advantage diminishes after passivation of the alloy surfaces.