Cariostatic Effects of Three Types of Phosphates When Fed Singly or in Combinations in the Diets of Rats

¹ Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts

The phosphorus content of a caries-producing diet was doubled to 0.8 per cent by additions of either sodium orthophosphate, metaphosphoric acid, or sodium trimetaphosphate, either singly or together on an equiphosphorus basis. These eight diets were fed to groups of thirty rats for 13 weeks beginning when they were 8 days old.

The following caries scores were observed: control 17.3, ortho-9.1, meta-5.5, trimeta-0.8, ortho-meta-7.4, ortho-trimeta-4.5, meta-trimeta-1.7, and ortho-metatrimeta-2.2.

All three phosphates were cariostatic when fed singly, the orthophosphate being the weakest and the trimetaphosphate the strongest.

The cariostatic effect of orthophosphate and metaphosphate when fed together on an equiphosphorus basis was additive.

The cariostatic effects from feeding trimetaphosphate with either orthophosphate or metaphosphate were more than additive, indicating that the trimetaphosphate exerted a synergistic effect. A similar effect was noted when all three phosphates were fed together.

The kidneys of all rats that were fed phosphate-fortified diets were as much as 24 per cent (males) and 34 per cent (females) heavier than the control group. The trimetaphosphate had less effect on kidney weight than the other phosphates; in fact it appeared to counteract the renal enlargement resulting from these phosphates.

A diet fortified with equal amounts of these phosphates is more physiologic, and almost as cariostatic, as a diet fortified with sodium trimetaphosphate alone.