[Experimental studies on the ultrastructure and chemical composition of enamel in dental fluorosis]

Young growing rats were maintained on drinking water containing different amounts of fluoride (0, 45, 100 and 113 ppm of F) for 70 days. Ultrastructural and chemical changes in the incisor enamel were investigated using scanning electron microscopy combined with a microincineration technique with a low temperature asher and by means of chemical analyses. The enamel formed during high fluoride exposure showed marked hypocalcification, that is, the crystallite density in the prism core as well as in the interprismatic region was lower than that of control animals. The organic constituents appeared to increase in those regions. These changes were evident in the outer enamel layer. Such results following fluoride administration were confirmed by chemical analyses, that is, calcium and inorganic phosphorus contents in the enamel decreased, whereas the amount of organic carbon in the enamel increased as the fluoride concentration in drinking water became higher. The results obtained in the present study appear to indicate that fluoride interferes with the process of enamel maturation. The mode of fluoride action was discussed with special reference to the recent findings about enamel formation.