OKUMURA, TSURUKICHI : Tokyo Dental College, Tokyo, Japan (July 16, 1939).

 [For himself and co-workers: B. MAKAI, F. SUGIYAMA, W. YONEZAWA, and K. HASEGAWA.]

(1) Two kinds of bacteria that play important parts in the etiology of caries have been isolated and cultivated from the oral bacterial flora. One, (a) Gram-positive, brings about decalcification of dental tissues; the other —discovered in this research—(b) Gram-negative, liquefies the organic sub­stance, and forms caverns (liquefaction foci) in decalcified dental tissues. (2) The decalcifier (a) is L. acidophilus and is named, from the standpoint of bacterial terminology and caries etiology, Lactobacillus odontodecalcificans. The liquefier (b) is Aerobacter cloacae, and is named Aerobacter odontolyso­genis. (3) With these two kinds of bacteria artificial caries has been pro­duced in vitro. In experimental studies the combined actions of these two kinds of bacteria induced main carious changes in dental tissues. (4) The crevices in carious dentin result from heavy infection by caries-producing bacteria, leading to the separation of dentinal lamellae. Coloration of carious lesions is due to absorption of pigments from foods and drinks, not to bacterial influence. (5) The acid produced chiefly in caries by these bacteria, and which causes decalcification, is succinic acid.

Reference: Kitasato Arch. Exp. Med., 15, 124, 1938.

ORBAN, BALINT : Dental School, Northwestern University, Chicago, Ill. (Sep. 19, 1938).

There is an intimate relation between caries and structural deficiency of teeth. Enamel lamellae are defective calcification areas and cracks, which may lead into dentin. In these cracks, tissue grows to form lamellae, the outer part of which may become hornified and thus prevent ingrowth of bacteria. If the outer part of an enamel lamella is not hornified, bacteria readily grow into the organic matter and rapidly pass into the dentin, there finding favorable medium for growth. This may explain some acute penetrating caries, where the enamel shows only a small opening but underlying dentin is extensively destroyed.

References: Z. Stom., 1925, 1926; J. Am. Den. Assoc., 1927; Arch. Kinderh., 1935.

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