Effects of N-Doped TiO₂ Thin Films on Corrosion Resistance of Stainless Steel Orthodontic Brackets in Artificial Saliva

N-doped TiO₂ thin films were prepared on 316L stainless steel orthodontic brackets using the radio frequency magnetron sputtering method. The microstructure and composition of specimens were analyzed by field emission scanning electron microscope equipped with energy-dispersive spectroscopy and x-ray diffraction. The corrosion resistance of the as-prepared samples was evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy, and a static immersion test in simulated oral solutions. Results showed that N-doped TiO₂ thin films had a nanosized anatase structure, with a uniform and compact surface. In artificial saliva and 1.23% acidified phosphate fluoride solutions, the as-prepared thin films lowered the corrosion current density and increased the polarization resistance, indicating improved corrosion resistance. The Ni and Cr out-diffusion levels were far lower than the recommended daily doses, indicating the N-doped TiO₂ thin films may be safe for clinical use.