Comparison of the Effects of Two Topical Fluoride Regimens on Demineralized Enamel in vivo

The purpose of this investigation was to study the intra-oral remineralization of acid-softened enamel by a NaF dentifrice compared with that from a combination of topical F agents. Bovine enamel slabs were demineralized with 0.1 mol/L lactic acid at pH 4.0 for 14 hr and then mounted in a removable mandibular appliance. Control slabs were worn for 96 hr by seven adult males who brushed daily with a F-free dentifrice. Test slabs were brushed with a NaF dentifrice 4 x / day or with the same dentifrice 4 x /day and a 0.02% APF mouthrinse and a 0.4% SnF₂ gel which were applied oncelday for three days. The natural dentition was also brushed with the NaF dentifrice during both test periods. Microhardness testing was performed on sound enamel, and after acid-softening, intra-oral exposure (IOE), and acid resistance testing (ART) in 0.01 mol/L lactic acid at pH 4.0 for 24 hr. Control and test slabs were etched with 0.5 mol/L HClO₄ for from 15 to 60 sec. The F content was measured with a F electrode and PO₄ by spectrophotometry. Contact microradiography and image analyses were performed on control and test slabs so that changes in mineral content resulting from treatment could be assessed. Both test groups were significantly harder after both IOE and ART than were controls, but no differences appeared between the effects of the two test groups. The F content of control slabs was significantly less than that of both test groups, and the combination-treated slabs showed greater F than did the dentifrice-treated slabs. Microradiographs revealed a higher mineral content in the basal 2/3 of combination-treated lesions, while diffuse mineral deposition occurred, especially subjacent to the surface in the dentifrice-treated lesions. Control lesions showed little added mineral.