Chemical and Morphological Aspects of Fluoride Acquisition by Enamel from Topical Application of Ammonium Fluoride with Ammonium Monofluorophosphate

Abstract

In vitro topical application for 5 min or 6 h of 1.5 M ammonium fluoride with 1.5 M ammonium monofluorophosphate (MFP) to [human] enamel was studied at pH 7.0 and 4.6. After 5-min treatments, fluoride penetrated over 10 .mu.m, but < 20 .mu.m into the enamel. More fluoride deposition and penetration over 20 .mu.m resulted from the 6-h treatments. Most fluorapatite was formed after a 6-h treatment with the neutral solution. Treated enamel surfaces were studied in the scanning electron microscope before and after KOH equilibration for removal of calcium fluoride. The electron micrographs were compared with others which were obtained from enamel treated for the same time with 1.5 M ammonium fluoride or 1.5 M ammonium MFP or 1.5 M ammonium fluoride with 1.5 M ammonium orthophosphate at pH 7.0 or 4.6. The most extensive dissolution-precipitation reactions, with considerable calcium fluoride formation, occurred relative to the application of ammonium fluoride alone. Addition of ammonium MFP or orthophosphate to ammonium fluoride solutions reduced the extent of visible changes. Application of ammonium MFP alone caused very limited or no visible change.