Effect of topical fluoride and fluoride varnish on in vitro root surface lesions

PURPOSE: To evaluate the effect of a fluoride varnish on demineralization and remineralization of root surfaces in vitro. METHODS: 80 caries-free teeth were selected from a large pool of extracted anterior and premolar teeth from elderly patients. Acid resistant nail varnish was painted on all surfaces except for a window (l x 4 mm) on the buccal or lingual root surfaces. Teeth were randomly divided into four treatment groups: Control: washed with deionized/distilled water; Daily gel: treated with Karigel-N (5,000 ppm) for 4 minutes daily; Weekly gel: treated with Karigel-N for 4 minutes weekly; and Weekly varnish: treated with Duraflor (22,600 ppm) weekly (the varnish was removed 24 hours after each application). Teeth were then placed in a cycle of demineralization (6 hours at pH 4.3) and remineralization (17 hours at pH 7.0) for 21 days. Half the specimens of each group were brushed with no dentifrice for 10 seconds twice daily. Specimens were evaluated under polarized light microscopy and contact microradiography. The depth of each lesion and width of the remineralization bands were measured. An ANOVA model was used to assess the effect of different treatments. RESULTS: The control group had the deepest lesions and the daily gel group had the shallowest lesions. The weekly varnish group was found to have significantly shallower lesions than the weekly gel group. The varnish brushing subgroup had significantly deeper lesions than varnish non-brushing subgroup (P = 0.01). Remineralization bands were detectable in most lesions. There was no significant difference in band width between different groups (F = 0.634, P = 0.594). However, a significant difference was found when remineralization bands were calculated as percentage of lesion depth between different groups (F = 4.24, P = 0.001). The varnish non-brushing subgroup had significantly higher percentage than the control group, but daily gel non-brushing had the highest percentage. Brushing was a significant factor in the varnish group. Lesions were significantly shallower in the non-brushing varnish subgroup.