Children, in the fifth school grade (mean age 11 years) in a fluoridated water area, self-applied acidulated phosphate-F gel (1.2% F) in custom-fitted mouthpieces on 5, 10, or 25 consecutive school days. Enamel F uptake, penetration, and retention were determined from analysis of 1,257 deciduous teeth exfoliated during and after the applications. F penetrated to 200 micrometer in enamel exposed to 25 applications of the gel and increased approximately 2,600 ppm at a 5 micrometer depth. Concentrations of F declined for approximately eight months after which levels stabilized, resulting in a 1,600 ppm increase of firmly bound F.

Three groups of approximately 200 children, consuming fluoridated water since birth, were given either 5, 10 or 25 consecutive topical applications with an APF gel (1.2% F, pH 3.2) in mouthpieces. After 1 year, mean DMFS increments were 7.2%, 30.4% and 35.3% less respectively for the three groups as compared with untreated control groups. Although enamel fluoride levels remained high after the 1st year, differences in dental caries increments between treated and control groups were too small to show group differences. The results suggest that in a fluoridated area, when caries activity is low, it would be difficult to show a long-term anticaries effect by increasing the fluoride concentration in sound enamel by a short series of self-applied topical fluoride applications.

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