Bacteriologic Studies of the Advancing Dentinal Lesion

Abstract

In view of the confusion regarding the nature of the bacterial flora of the advancing carious front in dentinal caries, it has been difficult to define the reactions that produce the lesion in this tissue. A bacteriological study of the advancing carious front in dentin showed that only three groups of micro-organisms (cocci, lactobacilli, and actinomyces) could be isolated regularly. Over 90% of the cultivable bacteria was made up of Gram-positive cocci, half of which were caseinolytic but none were active against more resistant proteins such as decalcified dentin. The cocci were composed of enterococci and micrococci. Lactobacilli made up 5% of the cultivable bacteria. The various strains were nearly homogenous in their reaction, but were not identical with any described species. Anaerobic filamentous micro-organisms were isolated regularly. The characteristics of these micro-organisms were homogenous and typical of the genus Actinomyces, although they did not agree exactly with any defined species. The actinomyces acted upon dentin to produce a dark-brown pigment, resembling that often seen in natural caries. No pigment was produced from other protein. The role of the 3 groups of micro-organisms in dental caries is discussed.