Crystallographic structure of enamel surfaces treated with topical fluoride agents: TEM and XRD considerations

The crystallographic structure of surface coatings produced by three topical fluoride agents deposited by a single application on intact human enamel surfaces was investigated by light- and dark-field transmission electron microscopy, as well as by electron and x-ray diffraction. The agents studied were an acidic silane fluoride lacquer, a neutral NaF lacquer, and an APF gel. The smallest coherently diffracting particles were CaF2 microcrystallites 4-15 nm in diameter. Large apatite-like crystals, approximately 1 micron in length, were also observed in the outer surface coating produced by the silane fluoride lacquer.