Abstract
Cox, Matuschak, Dixon, and Walker 1 produced mottled enamel in rat molars by daily individual feedings from birth of relatively high doses of fluorine to suckling rats. The first two molars, which normally are extruded at 19 days, were affected; the third molars, which appear on the thirty-fifth day, were apparently normal.
Miller 2 has shown that the development of dental caries is inhibited by 250 p.p.m. of sodium fluoride or 500 p.p.m. of calcium fluoride in a caries-producing ration fed to rats 28 days old. His ration was based on coarse rice.
In a confirmatory study of Miller's finding a ration of corn meal 66, whole milk powder 30, alfalfa meal 3, and sodium chloride 1 was fed to rats weaned at 21 days. Two groups, 22 and 23 rats, respectively, made up of litter mates, were used. One group had 250 p.p.m. of sodium fluoride in the ration. All were sacrificed after 8 weeks.
On examination of the teeth before they were sectioned, it was found that the enamel of the third molars of 19 out of 22 rats that had received added fluorine showed a faint diffuse milkiness. None of the first or second molars was affected. No milkiness was observed in any teeth of the control rats. No difference could be seen in the enamel when the teeth were sectioned by the method of Cox and Dixon. 3
This discovery of mottled enamel in the third molars of rats makes it possible to produce preferential decay in a rat mouth if the protective action of fluorine 4 is exerted by such late inclusion in the diet. On the other hand, failure to prevent caries in the third molar would indicate that fluorine exerts its protective action earlier in tooth life.
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