Influence of Fluorides on the Dynamics of Galvanic Corrosion of Titanium and a Co-Cr-Mo-Alloy

Fluoride exposure in the course of daily dental care can interfere severely with the galvanic corrosion behaviour of implant materials. The dynamics of the response to a spontaneous fluoride exposure are particularly interesting. To investigate these dynamics, the response of two electrochemical couplings - Ti/Ti and Ti/CoCrMo - to the addition of various fluoride concentrations was recorded via electrochemical noise measurements. Both a neutral and an acid environment were considered. Later, an optical surface analysis and a determination of the mass loss of the samples were performed. While Ti/CoCrMo was not affected in its electrochemical behaviour, Ti/Ti did respond to a fluoride exposure. Depending on the pH and fluoride concentration, the reaction varied from temporary deterioration of the passivation layer with subsequent repassivation to active corrosion paired with significant mass loss of the samples. In conclusion, high fluoride concentrations and low pH should be avoided for the electrochemical coupling Ti/Ti, especially in the context of long-term exposure. In contrast, the coupling Ti/CoCrMo proved to be extremely resistant to fluorides in terms of its galvanic corrosion behaviour. Keywords: fluorides, galvanic corrosion, titanium, CoCrMo, implant, dynamics, pH