Fluoride profiles in different sites of approximal surfaces of second primary molars after topical application of acidulated phosphate fluoride gel in vivo.

Thirty-four (17 paired) extracted second primary molars were obtained from 17 individuals (9 boys and 8 girls) aged from 9 yr 2 months to 12 yr 7 months. A tooth on one side was extracted as a control, and an acidulated phosphate fluoride (APF) gel was then applied to the paired contralateral second primary molar. Three months later, the experimental tooth was extracted. Nine sites were assayed by a microsampling technique from small areas of the approximal enamel surface. The fluoride and phosphorus concentrations were determined by a fluoride electrode and by colorimetric procedure, respectively. Fluoride concentrations were higher in the teeth treated with the APF gel than in the control teeth. The highest fluoride uptake was observed in the central area of the approximal surfaces. Deeper areas (> 10 microns) had a marked uptake of fluoride as compared with surface areas (< 3 microns). It was concluded that the APF gel application increased the fluoride levels of approximal tooth surfaces, particularly the mid-central site, of second primary molars, even at 3 months after application.