Dental plaque fluoride and pH in children exposed to different water fluoride levels

The aims of this study were to determine plaque fluoride concentrations in children not exposed to topical fluorides but to different fluoride levels in the drinking water (0.1 and 2.0 ppm), and to observe whether plaque fluoride was related to plaque pH. Twenty-five children (6 to 7 years old) were selected from two rural villages in Brazil. A sub-set of subjects was examined for resting and fermenting plaque pH before sampling. A maximum of 14 sites was studied in each subject (vestibular and interproximal of first molars and central incisors). Plaque fluoride was extracted and measured with an inverted fluoride electrode under oil. Amounts of plaque were determined by protein analysis. Mean values in the 0.1 ppm village were 1.3 ngF/mg of plaque wet weight (SD = 1.1) and in the 2.0 ppm village 2.5 ngF/mg (SD = 2.1) and were not statistically different (Kruskal-Wallis test, P = 0.09). Plaque fluoride varied considerably from site to site in the same mouth. Combining sites in all subjects, plaque fluoride concentrations were positively related to resting and fermenting pH (regression analysis, P< 0.01-0.001, adjR2 = 0.12-0.31). On an individual basis the same trend was found for fermenting, but not for resting pH. In conclusion, our findings showed a moderate influence of water fluoride upon dental plaque fluoride concentrations and give some support to the theory that low fermenting pH may contribute to the release of bound plaque fluoride.