Aim: corrosion of NiTi wires in the oral cavity has been a matter of discussion in some in-vitro studies but in-vivo tests about corrosion of NiTi wires have been rarely investigated. We designed an in-vivo study to evaluate corrosion behavior of retrieved NiTi wires compared with as-received wires.
Methods: Considering our criteria, 15 participants demanding orthodontic treatment entered the study, two NiTi SE(G&H) wires were inserted in bracket slots and band tubes and two passively in auxiliary tubes of molars. After 2 months wires were retrieved and were evaluated regarding clinical conditions (tarnish, deformation). Then potentiodynamic test performed on distal segment of 60 retrieved wires and Rp test (polarization resistance test) for all specimens including retrieved and as-received wires. Non parametric tests were used to compare retrieved and as-received wire groups.
Results: Retrieved wires showed clinically and electrochemically significant corrosion compared with as-received wires (p<0.05). All retrieved wires showed signs of tarnish which was more in lower arch. Among all retrieved wires, 5 wires showed deformation, 3 from lower arch and 2 from upper arches. One of recent two wires belonged to not-engaged group.
Conclusion: Despite of adequate corrosion resistance, NiTi wires, engaged or not engaged will corrode electrochemically
in oral enviroment and should be noticed in clinical use.