Corrosion behavior of dental titanium restrations and implant in fluorode-containing solution

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Titanium is used as a metal for biocompatible materials such as the dental implant or restorations because of an excellent chemical stability. However, the corrosion of Ti in prophylactic fluoride-containing environment comes into a problem. To clarify the effect of fluoride concentration and pH on the corrosion behavior of Ti, Ti-6A1-4V and Ti-6AI-7Nb, anodic polarization tests and immersion tests were carried out in NaF solution of various concentrations(0.05%-2.0%) and pH values(2.0-7.2). The concentrations of dissolved Ti in the test solutions were analyzed by inductively coupled plasma mass spectroscopy. The results showed that corrosion resistance of Ti or Ti alloys markedly decreased in the acidic solution as the fluoride concentration increased. There were obvious limits of fluoride concentration and pH value at which the corrosion behavior of titanium changed from "Non- corrosive" to "Corrosive". This relation indicates whether Ti and Ti alloys will corrode or not, if the fluoride concentration and pH value are known in the concerned environment. The corrosion of Ti in the solution containing fluoride depended on the concentration of hydrofluoric acid (HF). When the HF concentration in the solution was higher than about 30 ppm, the passivation film of the Ti was destroyed.In the fluoride-containing acidic solution, corrosion resistance of Ti and Ti-6AI-7Nb alloy were similar but that of Ti-6AI-4V alloy was inferior to them. Ti-0.2Pd and Ti-10Mo-0.2Pd alloys had a higher corrosion resistance than pure Ti, Ti-6AI-4V and Ti-6AI-7Nb alloys in the fluoride-containing acidic solution. It is thought that corrosion resistance is improved because the surface enrichment of Pd promotes a repass ivation of Ti.