The Effects of Phosphates on Experimental Dental Caries: A Literature Review

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

(1) More than 100 studies have been conducted with rodents to evaluate the cariostatic activity of phosphates. Despite the fact that these studies were conducted with different animal species (rats, cotton rats, hamsters) and with different strains within each species, using different cariogenic diets and under different laboratory conditions, and although the caries were evaluated by several techniques, the evidence is nearly unanimous that phosphates are effective anticaries agents in rodents.

(2) Phosphates differ in cariostatic activity depending upon the type of anion (cyclic-, trimeta-, tripoly-, hexameta-, ortho-, and pyro-), the activity decreasing approximately in the order given.

(3) Phosphates of the same series differ in cariostatic activity depending upon the type of cation (H, Na, K, Ca, Mg), the activity decreasing approximately in the order given.

(4) Sodium chloride appears to potentiate the cariostatic activity of insoluble phosphates, especially when baked together in bread.

(5) Phosphates have been found to have significant cariostatic activity when administered to rodents (a) freely mixed in the diet, (b) imbedded in hard fat and mixed in the diet, (c) baked in bread and mixed into the diet; to a lesser degree when (d) dissolved in the water supply or (e) delivered into the stomach by intubation. The phosphates with near-neutral pH do not appear to be cariostatic when applied in concentrated solutions directly to the tooth surface.

(6) The cariostatic effect of phosphates appears to be due largely to a local action on the tooth as these phosphates pass through the mouth, or a systemic-local action after the phosphates return to the mouth in the saliva. The purely systemic or metabolic effect of phosphates has not been investigated adequately.

(7) There appears to be no absolute correlation between the cariostatic action of phosphates and their water solubility, their buffer activity, or their chelating capacity. However, such relationships may exist between compounds of the same series (e.g., orthophosphates).

(8) The cariostatic effect of some phosphates appears to be exerted on the structure of the enamel, possibly by an initial demineralizing and subsequent remineralizing process, producing changes in morphology as well as in surface luster.

(9) The optimum level of diet supplementation has not been determined accurately. Certainly it varies with the cariostatic activity of each phosphate. Present evidence indicates that the addition of 0.4 gm. of phosphorus to each 100 gm. of diet is quite effective for rodents. This is equivalent to about 2 per cent of Na₂HPO₄, and is equivalent to doubling the phosphorus content of the diet. This is really not excessive, for one would have to triple the phosphorus content of white flour and white rice to raise the phosphorus to whole-cereal levels.

(10) The adhesiveness or retentiveness of the phosphates on the surfaces or in the pits and fissures of teeth seems important. Compounds that are themselves retentive or that are imbedded in materials which permit the slow release of the phosphate appear to be most effective.

(11) Phosphates exert an additive effect when administered with fluorine in the control of dental caries. This indicates that the mechanism of the cariostatic action of phosphates may be different from that of fluorine. It also suggests that experiments should be conducted to establish the possible public health importance of a combination of fluoridated water and phosphate-supplemented foods.

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