Tzu-Hsin Lee

Ion release from NiTi orthodontic wires in artificial saliva with various acidities

NiTi orthodontic wire products from different manufacturers would have different corrosion resistance. We assayed the corrosion resistance, in terms of ion release, of different NiTi orthodontic wires in artificial saliva with various acidities. Four types of as-received commercial NiTi orthodontic wires were immersed in artificial saliva (37 degrees C) at pH 2.5-6.25 for different periods (1-28d). The amount of Ni and Ti ions released from NiTi wires was determined using an atomic adsorption spectrophotometer. Surface morphology and roughness of wires were related to the corrosion resistance. Results showed that the manufacturer, pH value, and immersion period, respectively, had a significantly statistical influence on the release amount of Ni and Ti ions. The amount of Ni ions released in all test solutions was well below the critical value necessary to induce allergy and below daily dietary intake level. The amount of Ti ions released in pH>/=3.75 solution was mostly not detectable, representing that the TiO(2) film on NiTi wires exhibited a good protection against corrosion. Pre-existed surface defects on NiTi wires might be the preferred locations for corrosion. The NiTi wire with the highest release amount of metal ions had the maximal increase in surface roughness after immersion test, while a rougher surface did not correspond to a higher metal ion release.

Corrosion resistance of different nickel-titanium archwires in acidic fluoride-containing artificial saliva.

OBJECTIVE To test the hypothesis that different nickel-titanium (NiTi) archwires may have dissimilar corrosion resistance in a fluoride-containing oral environment. MATERIALS AND METHODS Linear polarization test, a fast electrochemical technique, was used to evaluate the corrosion resistance, in terms of polarization resistance (R(p)), of four different commercial NiTi archwires in artificial saliva (pH 6.5) with various NaF concentrations (0%, 0.01%, 0.1%, 0.25%, and 0.5%). Two-way analysis of variance was used to analyze R(p) with the factors of archwire manufacturer and NaF concentration. Surface characterizations of archwires were analyzed using scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. RESULTS Both archwire manufacturer and NaF concentration had a significant influence on R(p) of NiTi archwires. Different surface topography was present on the test NiTi archwires that contained the similar surface chemical structure (TiO(2) and trace NiO). The surface topography did not correspond to the difference in corrosion resistance of the NiTi archwires. Increasing the NaF concentration in artificial saliva resulted in a decrease in R(p), or corrosion resistance, of all test NiTi archwires. The NiTi archwires severely corroded and showed similar corrosion resistance in 0.5% NaF-containing environment. CONCLUSIONS Different NiTi archwires had dissimilar corrosion resistance in acidic fluoride-containing artificial saliva, which did not correspond to the variation in the surface topography of the archwires. The presence of fluoride in artificial saliva was detrimental to the corrosion resistance of the test NiTi archwires, especially at a 0.5% NaF concentration.

Corrosion Behavior of titanium-containing Orthodontic Archwires in Artificial Saliva: Effects of Fluoride Ions and Plasma Immersion Ion Implantation Treatment

The aim of this study was to investigate the effects of fluoride ion concentration and plasma immersion ion implantation (PⅢ) treatment on the corrosion behavior of different titanium (Ti)-containing dental orthodontic archwires (including Ni-Ti, Ni-Ti-Cu, Ti-Mo-Zr-Sn, and Ti-Nb alloys) using cyclic potentiodynamic polarization curve measurements in acidic artificial saliva. Different NaP concentrations (of 0%, 0.2%, and 0.5%), simulating the fluoride contents in commercial toothpastes, were added to the artificial saliva. The PⅢ surface treatment was carried out in a mixed Ar/N2 environment with an implantation density of 5×10^17 ions/cm^2. Surface characterization was analyzed using x-ray photoelectron spectrometry. Cyclic potentiodynamic polarization curves showed that the presence of fluoride ions destroyed the protective ability of the TiO2 film on the Ti-containing archwires, thus significantly decreasing the corrosion resistance of the tested alloys. Among the tested Ti-containing archwires, the Ni-Ti and Ni-Ti-Cu archwires were more susceptible to fluoride-enhanced corrosion, while the Ti-Nb archwire showed the lowest susceptibility. Furthermore, the PⅢ surface treatment improved the corrosion resistance of the tested Ti-containing archwires in acidic artificial saliva, by decreasing the corrosion rate and anodic current density.