Effect of pH on fluoride penetration into natural human plaque

Since recent studies have demonstrated that penetration profiles of fluoride into plaque falls from the saliva plaque interface towards the enamel, it was hypothesized that charged components may restrict the inward diffusion of fluoride i.e., protonated fluoride and may penetrate more effectively than fluoride ion. Therefore, in this study, we investigated the effects of pH on fluoride uptake and distribution in natural undisturbed human plaque formed in vivo by means of the Leeds in situ device. At pH 3 significantly less fluoride was present throughout the plaque layer compared with pH 7. Similar profiles were seen in the plaque produced over 1 week and 3 weeks. These results may be due to binding to components of the plaque matrix via hydrogen bonding. Protonation of bacterial cell surfaces may also lead to binding of the ionized portion of fluoride. In conclusion, low pH affected the short-term fluoride uptake from a 1,000 ppm fluoride solution.