Fluoride retention in sound and demineralized enamel in vivo after treatment with a fluoride varnish (Duraphat).

The retention of alkali soluble (CaF2) and alkali insoluble (fluorapatite) fluoride in sound enamel and demineralized enamel 2 wk after application of Duraphat was investigated in a group of orthodontic patients from whom pairs of homolog premolars were to be extracted. Demineralization of the enamel was induced during a 4-wk period prior to application of fluoride by applying orthodontic bands to the premolars. The bands also remained attached to the teeth during and after application of fluoride (2 wk) to maintain a cariogenic environment. Three consecutive enamel layers (approximately 5 microns) were subsequently etched off. A significant uptake of fluoride in the first and second layer of sound enamel and in all the three enamel layers of demineralized enamel was found. More fluoride was found in demineralized enamel and a higher proportion of this fluoride was found to be in an alkali insoluble form compared with the fluoride in sound enamel. The SEM study showed a rough enamel surface after three consecutive acid etchings. The etching pattern differed within the etched area. It was suggested that the variation in etching pattern might be due to differences in orientation of the crystallites and the original surface morphology.