Influence of the microstructure on electrochemical corrosion and nickel release in NiTi orthodontic archwires

• The phases present in the NiTi affect to the corrosion and the nickel release.
• The increase of the nickel favors the austenitic phase in the orthodontic wires.
• The presence of the martensitic phase improves the corrosion resistance.
• Martensitic structures present lower Ni release into saliva than austenitic ones.

The aim of this work was to determine the influence of the present phases and the chemical composition on the corrosion behavior and the nickel ion release of the NiTi orthodontic archwires. Eight Ni–Ti archwires from six commercial brands, in the as-received condition, were studied. The chemical composition, roughness, microstructure and the proportion of the phases as well as the corrosion behavior were analyzed for each archwire. The nickel ion release was characterized in artificial saliva immersion settings ranging up to 4 weeks. The results show that the presence of the martensitic phase improves corrosion resistance and significantly decreases Ni release into exterior medium in comparison with the austenitic specimens. In spite of the partial loss of superelasticity produced in the martensitic phase, it could be of great interest for biomedical applications, as it could minimize sensitization and allergies and improve biocompatibility and corrosion resistance of NiTi shape memory alloys.