LEONARD, HAROLD J.: School of Dental and Oral Surgery, Columbia Univer­sity, New York City (Aug. 15, 1939).

Three factors cause susceptibility to dental caries : (1) Sugar or starch retained in the mouth for considerable periods; (2) lack of lactobacillus-in­hibiting agent in saliva; (3) lack of sufficient phosphate in saliva, for con­siderable periods, to prevent solution of tooth salts by acid under bacterial plaques.

Factor (1) is influenced by (a) conditions favoring retention of sugar or starch, such as sucking of candy, working in flour or sugar dust, eating crackers (etc.) that stick to teeth for considerable periods ; (b) adequacy of tooth-cleansing care ; (c) interstices and irregularities in teeth that permit prolonged retention of food debris, in positions that are well protected from salivary cleansing-action, detergent action of mastication, and cleansing effect of tooth brushing. Factor (2), although not well established, is indicated by (a) the work of Jay et al.some mouths inhibit lactobacilli ; by (b) the work of Bibby and Sandholzer on lysozymes —bactericidal factors in saliva vary in potency in different individuals, and at dif­ferent times in the same individual depending on his physiological state; by (c) the condition that, in caries-free persons, lactobacilli are few or absent even though the diet contains carbohydrates ; and by (d) the facts that peroxidic com­pounds which are destructive of lactobacilli are present in saliva together with catalase, and that a factor which is a product of estimations of each is related to caries freedom or susceptibility in approximately 80 percent of 37 persons studied. Factor (3) is indicated by these facts : (a) average phosphate content and acid‑neutralizing power of salivas of caries-susceptibles are lower than in the caries- free ; (b) phosphate content of saliva may be lowered for considerable periods by ingestion of large amounts of candy or starch, or of any food that is quickly di­gested and absorbed ; (c) caries susceptibility varies inversely with vitamin-D intake, which directly affects absorption and retention of phosphate—and presum­ably its amount and nature in saliva.

References: J. Den. Res., 12, 473, 1932 ; 18, 238, 1939.

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