Changes in the Calcium and Phosphate Concentrations of Saliva and Inorganic Salt Solutions on Shaking with Calcium Phosphate

SALIVA from caries-susceptible and caries-free individuals shows few chemical differences, and it would be an extremely useful clinical test if some decisive criterion to distinguish between these two types of saliva were available. Karshan, 2 has stated that although the mg. per cent calcium and mg. per cent phosphorus are the same in saliva from both caries-free and caries-active individuals, the change in the concentration of these ions produced by shaking the saliva with excess powdered tricalcium phosphate is remarkably different. In stimulated saliva from caries-free individuals, 65 per cent of the calcium and 20 per cent of the phosphate were removed by shaking with tricalcium phosphate, whereas saliva from caries-immune individuals had 39 per cent of the calcium and 45 per cent of the phosphate removed by the same treatment. These surprising results prompted us to investigate this phenomenon further in an attempt to gain some insight into the chemical processes involved. On shaking saliva with tricalcium phosphate (Kahlbaum's reagent) we were unable to observe any decrease in phosphate but did obtain varying decreases in the calcium concentration. When an aqueous solution of calcium nitrate and sodium phosphate of approximately the same calcium and phosphorus concentrations as saliva was used, an analogous effect was observed, viz., an increase in phosphate and a decrease in calcium (Table I). The final pH of the solutions was approximately 5.60.