Observations on Induced Caries in Rats

Abstract

The post-eruptive increase of fluorine in dentin and enamel has been observed in rats (1, 2) and in an adult dog (3). Fluorine has been found deposited posteruptively by the rat in molar enamel but not in dentin (4). In vitro experiments show powdered enamel and dentin (5, 6), as well as bone tissue (7) to have the property, in common with pure mineral phosphates (8,9,10), of adsorbing fluoride.The above in vivo experiments (1, 2, 3) are interesting from several aspects. First: They indicate that dentin and enamel may be modified chemically during post-eruptive tooth life or after calcification has been completed. Second: Although fluorine was ingested in quantities varying from 10 ppm. to 125 ppm. by rats (1) a relatively constant proportion between fluorine retained by the enamel and fluorine retained by the dentin was maintained, i.e., about 3.5 to 4.0 times as much fluorine was found present in the dentin as in the enamel. This would seem to be due to an orderly systemic process. It advances the hypothesis that similar chemico-physical properties may be attached to both adult enamel and to adult dentin. Third: The retention of ingested fluoride by teeth post-eruptively raises the question of the relation of such secondary fluorine deposits to caries resistance.Epidemiological evidence has demonstrated the caries inhibitory properties of fluoride in water ingested during the period of tooth calcification (11,12,13,14). An important point to emphasize in these studies (13,14) is the distinction made between certain minimum quantities of fluorine which seemingly improve the dental tissue, and somewhat higher levels, which produce the hypocalcification or hypocalcification and hypoplasia known as endemic dental fluorosis (mottled enamel). On the basis of physiological effects, it also seems necessary to differentiate between at least two forms of dental tissue fluoride, i.e., fluorine acquired during the formative life of the tooth (primary fluoride) and fluorine acquired during adult or post-eruptive tooth life (secondary fluoride). There is the possibility of a third form of fluoride, i.e., fluorine acquired by the exposed oral enamel through surface adsorption (adsorbed secondary enamel fluoride) (4).

The Caries-Fluorine Hypothesis and a Suggested Study to Test Its Application

“…demonstrated that rats fed casein plus fluorine had from 60 to 70 percent less caries than groups fed powdered milk and plain casein. These data show that resistance to caries is inherent in the rat, presumably in the enamel.McClure(44), in 1941, observed that the caries resistance of rats is correlated with the amount of fluorine in the diet; also that the fluorine content of the molar teeth of the experimental rats is changed in direct proportion to the amount of fluorine in the diet. It is of interest to note that commercial casein was found to contain 0.2 percent of fluorine (42).Cox et al(43) observed that diets containing up to 40 p. p. m. of sodium fluoride fed to pregnant rats significantly reduced the incidence of dental caries in their offspring, when compared with controllitters.…”

Effects of Frequency of Exposure to Iron-Sucrose on the Incidence of Dental Caries in Desalivated Rats

“…Ferric chloride added to drinking water (250 ppm) was observed to reduce the prevalence of dental caries; in con trast, ferric citrate was without effect, suggesting a role for anion in the cariostatic effect of iron [McClure, 1948]. In a series of experiments, Emilson and Krasse [1972] demon strated the cariostatic effect of ferric chloride and ferrous sulfate when added to diet and drinking water.…”