Composition, mechanical properties and demineralization of fluorosed teeth

Fluorotic enamel has subsuperficial porosities and high fluoride content. The latter could confer resistance to dental caries development in these teeth. Nevertheless, the mechanical properties and inorganic composition have not been studied in fluorotic teeth, which could be related with its response to the demineralisation process. Objective: To assess if there are differences in composition, mechanical properties and mineral loss in fluorotic teeth. Methods: From 49 sound (TF0) and fluorotic (TF1-4) third unerupted molar-teeth collected, coronal fragments and 2 enamel blocks (2x2, 4x2 mm) were obtained. Coronal fragments were pulverized and enamel was demineralised. Calcium, inorganic phosphorous (P_i) and fluoride content (%) was determined in the enamel acid extracts respectively by atomic absorption spectroscopy, spectrophotometry and specific electrode. The surfaces of the 2x2 mm enamel blocks were acid-etched for 15, 30, 60, and 120 seconds to remove successive layers from external to inner layers. The weight (g) of removed enamel was calculated from the found P_i amount, and this allowed the determination of the depth of removed enamel. Fluoride content in each layer (F mg/g) and in the total (F mg/cm³) removed enamel was determined. The 4x2 mm enamel blocks were subjected to a pH-cycling model. Changes in mineral content related to enamel hipomineralization and to the demineralisation process were determined by cross-sectional microhardness analyses. Results: No differences were found in calcium and P_i content between the assessed TF. There was found a fluoride distribution gradient from the surface to the inner enamel, being higher in the surface, irrespective of TF. An increase of fluoride concentration in enamel related to dental fluorosis severity was found (p<0.0001). Highly fluorotic teeth (TF3-4) are more hipomineralized and showed greater mineral loss (p=0.0283). Conclusion: Enamel hipomineralization of highly fluorotic teeth (TF3-4) could be related with its susceptibility to demineralisation instead of its fluoride content.