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 fluoridecontaining 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

The objective of this investigation was to study the compositional influence on the corrosion behavior of Ni-Cr-Mo dental casting alloys in acidic artificial saliva. Cyclic potentiodynamic and potentiostatic tests were used to evaluate the corrosion behavior of different Ni-Cr-Mo dental casting alloys in deaerated artificial saliva with pH 5 at 37 degrees C. Optical microscope observations were made following the cyclic potentiodynamic tests. Surface chemical analyses were characterized by X-ray photoelectron spectroscopy and auger electron spectroscopy following the potentiostatic tests. The results show that the corrosion resistance of the Ni-Cr-Mo casting alloys investigated is associated with the formation of passive film containing Ni(OH)(2), NiO, Cr(2)O(3), and MoO(3), on the surface. The pitting potential and passive range, respectively, were statistically different among the different Ni-Cr-Mo alloys. The Ni-Cr-Mo alloys with higher Cr ( approximately 21%) and Mo ( approximately 8%) contents had a much larger passive range in the polarization curve and were immune to pitting corrosion due to the presence of high Cr (maximum approximately 31-35%) and Mo (maximum approximately 12%) contents in the surface passive film. The presence of Ti lower than 4% in the Ni-Cr-Mo casting alloy had no effect on corrosion resistance. A pitting resistance equivalent (PRE) of about 49 could provide the Ni-Cr-Mo alloy with a good pitting corrosion resistance.

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