Enamel fluoride uptake and retention from intensive APF gel applications in vivo.

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.