Corrosion Resistance of Zr-ion Plating Ni–Ti Alloys in Fluoride-containing Environments

Objectives: Ni–Ti alloys are used widely in many medical fields because of their excellent properties such as shape memory, superelasticity, and good corrosion resistance. However, several studies have shown corrosion and discoloration of Ni–Ti alloys in fluoride-containing environments. Other reports have revealed that plating treatment of the Ni–Ti alloys contributes to corrosion prevention. This study investigated the influence of fluoride on Ni–Ti alloys from the viewpoint of corrosion behavior in artificial saliva and fluoride mouthwashes, and the differences in corrosion behavior between a new Zr-ion plating Ni–Ti arch wire and an untreated Ni–Ti wire.
Methods: Commercially available Ni–Ti arch wire and Zr-ion plating wire were used in this study. The anodic corrosion behavior was examined using potentiodynamic polarization measurements after immersion for 1 h in each test solution (artificial saliva, Bulter F Mouthrinse (fluoride ion concentration: 500 ppm), Ora-bliss (fluoride ion concentration: 900 ppm)). The electrochemical properties were determined. Surface properties of wires were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM).
Results: Zr-ion plating Ni–Ti wire in artificial saliva had a lower current density than the untreated Ni–Ti wire. In 900 ppm fluoride mouth rinse, its corrosion was highest in all conditions. The resistance of Zr-ion plating Ni–Ti wire was higher than that of untreated Ni–Ti wire. Surface analyses by SEM and AFM revealed small cracks in artificial saliva. By contrast, a large change in surface conditions was visible in 900 ppm fluoride mouth rinse for untreated Ni–Ti wire.
Conclusions: Zr-ion plating Ni–Ti arch wire showed higher corrosion resistance, suggesting that the Zr-ion plating treatment improved the corrosion resistance of Ni–Ti arch wire.