The Effects of Continued Exposure to Added Increments of Water-borne or Food-borne Fluoride upon the Rat

¹ University of Wisconsin, Department of Biochemistry, Madison, Wisconsin

The effects of administering various low dosages of water- and food-borne F^- to rats for extended periods of time have been investigated. These studies showed the following results. All levels of added F^- resulted in an increase in F^- content of the femurs and teeth. The amount of F^- deposited was directly proportional to the daily intake of F^- (µg F^-/gm body weight), regardless of whether it was given in food or water. However, from the viewpoint of dietary level, a concentration of F^- in water caused approximately the same F^- deposition as twice this level in food because water intake was double that of food. The F^- concentration in the femur and molar dentin gradually increased during the long treatment period. Of the tissues analyzed, F^- deposition was highest in the femur. Lesser amounts were found in the molar dentin, incisor dentin, and the enamel, in that order. A sex difference in F^- retention was described which appeared to be associated with the increased nutritional requirements imposed by pregnancy and lactation.

Contrary to the results of short-term experiments, extended exposure of the rat to moderate dosages of F^- was accomplished by a significant increase in what we have considered to be dental caries. These lesions, however, were present in the secondary dentin of the occlusal surfaces of the molars and do not appear to be analogous to human caries. Sound teeth were developed in the absence of supplementary F^- on a ration containing 0.5 p.p.m. F^-. However, it should be noted that these animals were from a relatively caries-resistant strain and fed a moderately cariogenic diet.

Added increments of F^- caused progressive increases in incisor enamel hypoplasia. Only mild hypoplasia occurred in the rats receiving F^- supplements of 1.2 p.p.m. in water and 3.0 p.p.m. in food. These low intakes of F^- produced F^- levels in the calcified tissues which were well below the toxic range for this species.