Objective: NiTi wires in different intra-oral locations serve in various corrosive biologic and mechanical conditions: forces from occlusion and engagement in slots, saliva composition and flow, and even temperature. None of in-vivo studies had studied effects of these variations on retrieved wires. We decided to be more specific about these factors and study corrosion behavior of NiTi wires used with different conditions in different locations of buccal cavity.
Methods: Fifteen participants demanding orthodontic treatment was entered the study. Two NiTi SE(G&H) wires were inserted in fixed appliance and two passively in auxiliary tubes of molars in every participant. After 2 months wires were retrieved and were compared with as-received wires. Then electrochemical impedance spectroscopy (EIS) test was performed on distal segments of wires after cutting in half. Rp (polarization resistance) was measured. Non-parametric statistical tests were performed and degree of significance was set to p<0.05.
Results: Rp in all retrieved groups was significantly lower than as-received wires. Rp of wires in lower arches was significantly lower than upper in engaged wires but not statistically significant in not-engaged. Rp was not significantly different between engaged/auxiliary or right/left wires.
Conclusion: Corrosion was significantly higher in lower arch in engaged wires but not in auxiliary wires. So, expensive surface treatment methods might not be as much critical for arch wires produced for upper arches. Alternatively, they can be recycled for use in lower arch with less concern; especially in the same patient.
Keywords: NiTi, EIS, arch, orthodontic wire