On the enamel surface, accumulations of filamentous organisms and Gram- positive and Gram-negative cocci are prominent, some of them producing high concentrations of acids from carbohydrates, and therefore may be considered potential causes of enamel decalcification. There are great variations in percentages of the various types of microorganisms in carious cavities, indicating absence of a specific bacterial cause of caries. The organic structures of enamel resist bacterial destruction. Characteristic formations of acid-resistant material—most marked in old teeth—are present in the superficial layers of the enamel surface of caries-resistant teeth. A certain type of pigmented plaque on teeth is associated with lessened susceptibility to caries.
References: J. Den. Res., 1931, 1932, 1934; J. Am. Den. Assoc., 1933, 1935; J. Am. Col. Den., 1935 ; A study of the filamentous bacteria of the mouth, Ph.D. Thesis, University of Rochester, 1935.