Fluoride Distribution Pattern Throughout Enamel and Dentine of Fluorotic Teeth

Since there is a linear relationship between dose of fluoride intake from drinking water and fluorosis index, an association between fluoride concentration in enamel and fluorosis index should be expected. Nevertheless, the scarce found data has suggested that dentine would be a better biomarker of systemic exposure to fluoride than enamel. Objective: To assess the fluoride concentration and its distribution pattern  throughout the enamel and dentine of fluorotic teeth, using the traditional acid-etching analysis method. Methods:  From 23 unerupted human third molars, presenting TFI 0-4, blocks of enamel and pulp dentin (2x2 mm) were obtained. Their surfaces were acid-etched for 15, 30, 60 and 120 seconds to remove successive layers from each tissue (enamel: from external to inner layers; dentin: conversely). Fluoride and inorganic phosphorous (P_i) were determined in each acid extract , respectively by specific electrode and spectrophotometricaly. The weight of  enamel or dentine removed was calculated from the found P_i amount, and this allowed  the determination of the depth of tissue removed (µm). The fluoride concentration in each layer was expressed in ppm (µg/g) and by volume of total removed tissue (µg F/cm³). Results: For enamel, a gradient of fluoride distribution was found with highest concentration at the dental surface, irrespective of TFI, but in dentin the fluoride concentration was uniform from the pulpal surface to the outer dentine. In all cases, fluoride concentrations in dentin were greater compared to enamel. A relationship between increase of fluoride concentration in enamel and dentine (expressed in ppm or by volume) and dental fluorosis severity was found, but dentine appeared to be more sensitive than enamel to differentiate the degree of fluorosis. Conclusions: The findings of this pilot study suggest that dentine may be a better biomarker of fluoride exposure than enamel because its fluoride concentration is uniform throughout dental structure, reflecting fluoride metabolism.