Corrosion of Ni-Cr-Mo alloys for fixed dental prostheses in an aqueous solution of 0.05% NaF and in commercial mouthwashes by means of EIS.

Abstract

-Ni-Cr-Mo alloys have been used as dental prostheses due their properties such as good mechanical strength, high corrosion resistance and also because they are economically viable. The corrosion protection of these alloys in salt solutions which are typical of physiological media is due to the phenomenon called passivation with an oxide superficial layer formation, particularly chromium oxides. This protective film, subjected to mechanical stress in a corrosive environment, can be broken partially releasing ions that have deleterious effects in a human body. Fluoride ions, existent in hygiene products, change the oral environment and their presence may enable the beginning of a localized corrosion process. The objective of this work is to evaluate the corrosion resistance of three Ni-Cr-Mo alloys, of different compositions: SC (73% Ni, 14% Cr, 8.5% Mo, 1.8% Be, 1.8% Al) SB (61% Ni, 25% Cr, 10.5% Mo, 1.5% Si) and W (65% Ni, 22.5% Cr, 9.5% Mo, 1.0% Nb, 1.0% Si, 0.5% Fe) in media containing fluoride which simulate oral rinse solutions. This study has been performed in solution of 0.05% NaF, NaCl 0.05% and commercial mouthwashes on pH 6.0 at 37°C using metallography analyses, immersion techniques, and electrochemical tests, impedance tests and analysis. SC, with the highest nickel and the lowest chromium content, does not passivate in the studied means showing a continuous increase in current density due to increasing potential, while the other alloys exhibit passivation range of 600 mV and passive current density 10 -6 A/cm 2 . In general, considering the immersion and electrochemical corrosion tests, it is concluded that the worst performance has been attributed to the alloy SC, while W and SB have shown the best performance and very similar behaviors.