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The corrosion behaviors of Ti, Ti-6Al-7Nb and Ti-6Al-4V alloys, and an experimentally produced Ti-0.5Pt alloy in 0.05％ to 2.0％ concentrations of Acidulated Phosphate Fluoride（APF）solutions（corresponding to 226 to 9,050 ppm fluoride at pH 3.5 or 3.6）were examined. While the corrosion of Ti, Ti-6Al-7Nb and Ti-6Al-4V alloys might occur easily even in a diluted 0.05％ APF solution, dissolution of Ti from the Ti-0.5Pt alloy was observed only in test solutions with APF concentration exceeding 0.2％. When Ti-6Al-7Nb and Ti-6Al-4V alloys were immersed in 2.0％ APF solution, their surfaces were entirely covered by compact corrosion products of Na 3 TiF 6 due to severe corrosion. As a result, Ti dissolution was prevented and the amount of Ti dissolved decreased. However, since Ti was covered by porous, large-sized corrosion products of Na 3 TiF 6 and that Ti-0.5Pt alloy was not covered with any corrosion product, the amount of Ti dissolved increased in the 2.0％ APF solution.

The corrosion behaviors of Ti and Ti-6Al-4V, Ti-6Al-7Nb, Ti-0.5Pt, Ti-6Al-4V-0.5Pt, and Ti-6Al-7Nb-0.5Pt alloys were examined using an electrochemical analyzer in artificial saliva containing 0.1 and 0.2％ NaF at a pH of 4.0. The SEM observations revealed that the surfaces of the alloys containing 0.5 wt％ Pt were not affected in fluoride-containing environments, whereas the surfaces of Ti, Ti-6Al-4V, and Ti-6Al-7Nb alloys were markedly rough. In artificial saliva containing 0.1％ NaF at a pH of 4.0, the amounts of Ti dissolved from the Ti, Ti-6Al-4V, and Ti-6Al-7Nb alloys were about 50 times larger than those of the alloys containing 0.5 wt％ Pt. The tensile strengths of the alloys containing 0.5 wt％ Pt were equal to or higher than those of pure Ti or the alloys without Pt. The Ti-0.5Pt, Ti-6Al-4V-0.5Pt, and Ti-6Al-7Nb-0.5 alloys are expected to be useful in clinical dentistry as new Ti alloys with high corrosion resistance and mechanical strength.

This study evaluated corrosion behavior of pure titanium and titanium alloy in the pseudo oral environment. It was suggested that pure titanium and titanium alloys were corroded by acid which produced by streptococcus mutans in oral biofilms with 500ppm fluoride on the titanium prosthetic appliance.