Materials and Methods : Sixty human caries-free premolars where randomly assigned into four groups of 15 specimens. The control group was washed with deionized/distilled water. Weekly gel (Kimia) was treated with APF gel (1/23%) for 2 minutes weekly, weekly gel (Sultan) was treated with APF gel (1/23%) for 60 seconds weekly, weekly varnish fluoride was treated with Durashield (2/26%). Specimens were then placed in a cycle of demineralization (pH= 4.3) for 6 hours and remineralization (pH= 7) for 17 hours. This pH- cycle was repeated for 3 weeks (21days). The teeth were sectioned buccolingually and evaluated under polarized light microscope. Then the depth of each lesion was measured from the deepest demineralization point of the lesion. The data were analyzed using Kruskal-Wallis and Dunn test for pairwise comparison .

Results : The control group had the deepest lesions (mean depth, 140±37micrometer). The varnish group had the shallowest lesions (mean depth, 60±37 micrometer) with a 75.3% reduction percent. However, there was no significant difference in the depth of demineralization between all fluoride treated groups. The difference between fluoride groups and the control group were significant.

Conclusion : Treatment of the enamel of permanent teeth with various topical fluorides significantly inhibited demineralization, but there was no significant difference between varnish or gel application .