KARSHAN, MAXWELL : Schools of Medicine and Dentistry, Columbia Univer­sity, New York City (May 11, 1939).

Salivary levels of calcium, inorganic phosphate, H-ion concentration, titratable alkalinity and CO2-capacity affect the destruction or solution of enamel by acids. The findings below indicate that salivas of persons free from caries provide greater protection, against solution of enamel by acids and hence against caries, than salivas of persons having active caries. Normal levels of calcium and inorganic phosphate in blood serum indicate that there is no apparent deficiency in the mechanism of calcification in individuals having active caries. Normal levels of H-ion concentration, CO2-content and CO2­capacity, in blood plasma of persons having active caries, indicate that caries is not associated with acidosis or alkalosis. Although no correlation has been found between composition of aqueous extracts and condition of teeth, ex­tracts of both enamel and dentin contain small amounts of calcium, phosphate, sodium and CO2-yielding material which could not be due to solution of contained apatite salts. Possibly these salts act as metabolites.

(1) In both stimulated and unstimulated salivas, mean values are higher in caries-free than in active-caries groups for CO2-capacity, total calcium, inorganic phosphate, and percent of calcium removed on shaking with ” commercial ” tribasic calcium phosphate. Mean values for total protein and for percent of protein and phosphorus removed, on shaking with tricalcium phosphate, are lower in stimu­lated salivas of caries-free than in active-caries groups. The differences between the means in all these respects are statistically significant. (2) Mean values are higher in caries-free than in active-caries groups in pH of stimulated and unstimu‑lated salivas, and in titratable alkalinity of stimulated salivas, the differences being small and of uncertain statistical significance. (3) Differences between caries- free and active-caries groups, in protein content and in titratable alkalinity of un­stimulated salivas, in ammonia content of stimulated salivas, and in percent of phosphorus removed on shaking unstimulated salivas with tribasic calcium phos­phate, are very small, and not statistically significant. (4) Salivary findings for groups of individuals having arrested caries were similar to those for caries-free groups. (5) Mean values for total calcium, inorganic phosphate and CO2-capa­city, in stimulated salivas of active-caries groups, resembled mean values for groups free f rom salivary calculus ; whereas for caries-free groups they were like those for groups tending to form heavy deposits of calculus, suggesting inverse relation­ship between occurrence of caries and tendency to form calculus. (6) No corre­lation has been found between caries and (a) levels of calcium, inorganic phosphate and protein in blood serum, or (b) pH, CO2-capacity and CO2-content of blood plasma. (7) Aqueous extracts of sound enamel and dentin from non-carious and carious teeth do not differ appreciably in mean values of H-ion concentration, or in contents of calcium, phosphorus, and CO2 (from carbonate or bicarbonate). (8) Enamel can be prevented from dissolving at any given level of H-ion concen­tration if sufficient calcium and phosphate are present. Enamel is about five times as soluble at pH 3.5—the level probably attainable by lactobacilli in the mouth—as at pH 4.5, the probable limit for other bacteria under natural conditions.

References: J. Den. Res., 1931, 1934, 1936, 1937, 1938 ; Am. J. Dis. Child., 1939.

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