Assessment of the electrochemical behaviour of Nickel-Titanium-based orthodontic wires: Effect of some natural corrosion inhibitors in comparison with fluoride.

The aim of this study is to assess the corrosion resistance behaviour of Nickel-Titanium-based orthodontic wires (NiTi) in different concentrations of Sodium Fluoride (NaF) and the corrosion's inhibitory effect of the extracts of some medicinal plants (essential oils, hydrosols and extract).In this study we used NiTi (3M) and CuNiTi (ORMCO, 35°C, California) orthodontic wires. The following electrolytes were prepared: Lactate Ringer solution with additions of 0.1%, 0.5% or 1% of Sodium Fluoride and the extracts of different plants: Artemisia, Syzygium aromaticum (Clove) and Celtis australis. Corrosion resistance was studied using anodic potentiodynamic polarisation and electrochemical impedance spectroscopy measurements. At the end of the experiment, microscopic images of wires were performed. ANOVA test with the comparison of Bonferroni and Tukey tests were performed to elucidate comparisons among all groups.The higher sodium fluoride concentration is related to negative corrosion potential for both NiTi and CuNiTi orthodontic wire. Hydrosols are associated to positive values of corrosion potential. CuNiTi has a lower corrosion resistance than NiTi.

The prescription of toothpastes containing sodium fluoride should be reduced especially for patients wearing fixed orthodontic appliances. Eugenol may be considered as alternative of sodium fluoride for orthodontic patients for its anti-microbial and anti-corrosive effects. Key words:Corrosion behaviour, Sodium Fluoride, Nickel-Tatanium, orthodontic wires, corrosion inhibitors, aromatical plants.