Possible Mechanisms of the Cariostatic Action of Phosphates by Way of the Saliva, Serum, and Lymph

¹ Director of Investigative Biochemistry, Jewish Hospital of Brooklyn, New York

The composition of blood serum (and presumably that of lymph) can be influenced by the diet, starvation, alkalosis, acidosis, hormones, and other factors. The composition of serum is related to the mineral composition of teeth and growing bones. Some relationships between composition of blood serum and that of saliva have been shown, but the evidence is scanty and incomplete. The composition of saliva influences the composition of enamel in adults and possibly that of dentin. Indirect evidence supporting this is the relationship established between the composition of the inorganic fluid and that of the solid. In addition, the composition of the solid has been shown to be related to the Ca:PO₄, citrate:PO₄, and the CO₃:PO₄ ratios by in vitro calcification of hypertrophic cartilage matrix.

Soluble phosphate added to the diet causes an increase in the serum-phosphate levels, which results in a reduced CO₃:PO₄ ratio. This change in serum brings about a low-carbonate mineral in growing teeth which is less soluble and, therefore, presumably, provides a more caries-resistant enamel. Phosphate added to the diet probably changes saliva composition not only by a systemic effect but also by direct solution in the oral fluids. Caries susceptibility may be reduced by several means: (1) Increasing the product of calcium and phosphate ions should decrease the solubility of tooth enamel. (2) The increase of phosphate should reduce the CO₃:PO₄ and the citrate:PO₄ ratios, which, in turn, would produce a less soluble enamel mineral. (3) Phosphate as a buffer may neutralize acids produced by bacteria and other cells in the oral cavity. (4) Phosphate may (a) affect the metabolic products and reproduction of micro-organisms and cells to bring about a caries reduction, and (b) affect the composition of the saliva secreted.