A pH-cycling model has been used to examine the effects of fluoride dentifrices on the saliva-mediated repair of early carious lesions in vitro. Fluoride reactivity was characterized by fluoride uptake, surface microhardness and lesion mineral content (microradiographic) analyses. The fluoride dentifrices, in particular the sodium and amine fluoride preparations, were found to be extremely effective in enhancing the remineralization and acid resistance of early carious lesions. The most prominent effect of the fluoride topicals, however, was found to be the fluoride enrichment of the remineralized enamel. The rank ordered efficacy of the fluoride dentifrices was NaF = AmF > MFP ≥≥ placebo. The remineralization of the early carious lesions was linearly associated with the increased surface hardening of specim