Electrochemical and Corrosion Properties of Ion-Implanted Orthodontic Wires

Objective: To assess electrochemical properties and degradation of CuNiTi orthodontic wires implanted with nitrogen ions. The ion-implantation treatment was developed to improve mechanical and frictional properties of conventional orthodontic wires.

Methods: Ion-implanted wires (Ion) (0.041 cm diameter, aprox. 0.21 cm² in area) were tested in aerated phosphate buffered saline at room temperature. Control commercial orthodontic wires — CuNiTi, NiTi, stainless steel (SS), and titanium molybdenum alloy (TMA) — were tested applying the same conditions. Ormco provided all wires. A continuous series of tests was done on each sample, which included open circuit test (OCT), electrochemical impedance spectroscopy (EIS), and cyclic polarization test (CPT). OCT and CPT were conducted following ISO 10271 Standard, and thus, the open circuit potential (E_OCP), zero current potential (E_Z), active peak potential (E_C), corresponding current density (I_C), breakdown potential (E_P), corresponding current density (I_P), and current density at E_Z+300mV (I₃₀₀) were reported. All potentials were in reference to a calomel reference electrode. Tests were performed in duplicate. Comparative visual inspection and microchemical analysis of the tested wires were carried out with a table-top SEM with an attached energy-dispersive x-ray spectrometer (EDS).

Results: Results are shown in Figure 1. E_p of Ion wires was higher than the one for commercial wires except for TMA, which did not break the passive layer. Notably, Ion wires had higher E_OCP, E_z, and E_p and lower I_p and I₃₀₀ than CuNiTi base-material wires. Ion wires also showed good repassivation. Only Ion and TMA wires did not show pitting after completing the electrochemical tests.

Conclusions: Ion-implanted wires showed excellent electrochemical and corrosion resistance responses, which were comparable if not better than those for commercial wires composed of different materials. Thus, Ion wires are mechanically-improved, promising candidates to be used in orthodontic treatments.

Supported by UMSOD Summer Fellowship Program.