Objective: Since further knowledge on caries inhibition/progression could be obtained from models evaluating the dynamics of fluoride (F) from dentifrice in dental biofilms, this double-blind, crossover, in situ study aimed to evaluate the effect of F dentifrice on biofilm acidogenicity and mineral ion concentration in the biofilm fluid, and on enamel demineralization. Methods: Ten volunteers wore palatal appliances containing 4 enamel blocks covered by a S. mutans test-biofilm. Appliances were immersed for 1 min in one of the treatment/groups: non-F dentifrice (negative-control) and F dentifrice (1100 µg F/g as NaF, silica-based); simultaneously, volunteers brushed their teeth with the assigned dentifrice. Appliances were placed in the mouth and after 30 min a rinse with 20% sucrose solution provided a cariogenic challenge. Before and 5 min after the rinse, pH of the test-biofilm was measured using a microelectrode. Forty-five min after the rinse the pH was again measured and appliances were removed. Test-biofilm from 2 layers (up to 1.25 mm and up to 2.5 mm from the biofilm surface) was collected for fluid analysis. Enamel surface microhardness was determined previously and after the test, and the percentage of surface microhardness change (%SMC) was calculated. Results: F dentifrice-treated enamel blocks showed a statistically lower %SMC (p<0.05). No significant difference was observed between F and non-F dentifrices in the initial pH (p>0.05), but both pH 5 and 45 min after the cariogenic challenge were lower for the non-F dentifrice (p<0.05). Split-plot ANOVA showed that, irrespective of test-biofilm thickness, F concentration in the biofilm fluid was higher while calcium and inorganic phosphorus concentrations were lower for the F dentifrice treatment than for the non-F dentifrice (p<0.05). Conclusion: The results suggest that the anticariogenic effect of F dentifrice could be associated to a high F concentration in the biofilm fluid and to a low acidogenicity.

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