Applicability of an In Situ Model to Evaluate Fluoride Mouthrinses

Objectives: In situ models have been successfully used in cariology research. The suitability of the “Piracicaba in situ model” has been demonstrated in studies assessing cariogenicity of carbohydrates and the anticaries effect of fluoride from toothpastes and professional use. In the present study, we are presenting preliminary data about dose-response of this model to fluoride mouthrinses, on enamel gain or loss of minerals.
Methods: In a double-blind, crossover, in situ study, 9 volunteers wore a palatal appliance containing 8 bovine enamel slabs, covered by a plastic mesh and exposed to 20% sucrose. Four slabs were sound and were treated with sucrose 8x/day to assess enamel demineralization; 4 slabs had incipient caries lesions and were treated with sucrose 3x/day to assess enamel remineralization. The tested mouthrinses (0, 250 or 1000 ppm F) were used 2 times/day. After 14 days, biofilm and the dental slabs were collected for analysis. Fluoride concentration was determined in biofilm fluid. On enamel, percentage of surface hardness loss (%SHL) (initially sound blocks), percentage of surface hardness recovery (%SHR) (initially carious blocks) and loosely-bound enamel fluoride concentration were determined. Model dose response was assessed by linear regression.
Results: F concentration in the fluid (uM) increased linearly (p<0.0001) with F concentration in the rinse (4.4±3.4; 38.3±15.7 and 468.7±357.3 for groups 0, 250 and 1000 ppm F, respectively). Significant linear correlations were also observed between loosely bound fluoride in enamel and F concentration in rinses (p=0.0005 and 0.0001 for sound and carious enamel, respectively). The effect of fluoride concentration in rinses on %SHL and %SHR did not reach statistical significance at p<0.05 (p=0.084 and 0.090, respectively).
Conclusions: These preliminary results suggest that the in situ model can present dose-response to assess fluoride rinses.