Fluoride retention in human enamel after a single phosphoric acid and mixed phosphoric acid/SnF2 application in vitro

Abstract

Pieces of enamel were treated with either an APF solution or a 1:1 mixture of APF/SnF2 (APF: 1.23 per cent F−, 0.1 M H3PO4; and SnF2: 2 per cent) for 4 min at 37 °C followed by 30 min washing. There was an increase of 1640 parts/106 in the fluoride concentration of APF-treated enamel. Most of the fluoride was, however, washed away within 24 h to a level of 230 parts/106. After 7 × 24 h the F concentration was of the same order: 280 parts/106. The initial increase in fluoride concentration was lower after a mixed topical application (1120 parts/106) but after 24 h the fluoride concentration was 510 parts and after 7 × 24 h 370 parts/106, although statistically not significant, higher than after a single APF-treatment. The higher F concentration may be due to the formation of more firmly-bound fluoride as a fluoridated hydroxyapatite. It is more probable that the CaF2 layer is protected by insoluble Sn compounds.