Purpose This study aimed to investigate the effect of sodium fluoride (NaF) on titanium corrosion using a biofilm model, taking environmental pH into account. Methods Streptococcus mutans cells were used as the artificial biofilm, and pH at the bacteria–titanium interface was monitored after the addition of 1% glucose with NaF (0, 225 or 900 ppm F) at 37 °C for 90 min. In an immersion test, the titanium samples were immersed in the NaF solution (0, 225 or 900 ppm F; pH 4.2 or 6.5) for 30 or 90 min. Before and after pH monitoring or immersion test, the electrochemical properties of the titanium surface were measured using a potentiostat. The amount of titanium eluted into the biofilm or the immersion solution was measured using inductively coupled plasma mass spectrometry. The color difference (ΔE*ab) and gloss of the titanium surface were determined using a spectrophotometer. Results After incubation with biofilm, pH was maintained at around 6.5 in the presence of NaF. There was no significant change in titanium surface and elution, regardless of the concentration of NaF. After immersion in 900 ppm NaF solution at pH 4.2, corrosive electrochemical change was induced on the surface, titanium elution and ΔE*ab were increased, and gloss was decreased. Conclusions NaF induces titanium corrosion in acidic environment in vitro, while NaF does not induce titanium corrosion under the biofilm because fluoride inhibits bacterial acid production. Neutral pH fluoridated agents may still be used to protect the remaining teeth, even when titanium-based prostheses are worn.
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