Effects of fluoride in remineralized human surface enamel on dissolution resistance

Remineralized surfaces of human tooth enamel were dissolved at constant rates in 10 mM acetic acid at pH 4.0, and in 10 mM EDTA at pH 7.4 in a system that prevented redistribution of dissolved F-. Surfaces remineralized 25 hours in 0.4 mM NaF (8 ppm F-) dissolved slower in acid or in EDTA than those remineralized in the absence of F-. The F- in three-hour remineralized surfaces had no effect on rates of mineral dissolution. Resistance to EDTA, as well as acid of 25-hour remineralized surfaces, indicates the occurrence of a maturation process, which may involve F- exchange for OH- ions in newly formed crystals. The results indicated that F- may slow caries by its action on remineralization if given sufficient time for this maturation.