Streptococci in Dental Caries

THE specific bacterial etiology of dental caries is still uncertain, in spite of the enormous amount of work directed to its elucidation. The only undisputed evidence available to date is that caries cannot occur in the absence of microbes.' The problem of bacteria associated with caries has already been investigated on three successive levels, comprising the direct environment of the carious lesion: (a) exploration of the vast flora of the saliva, (b) identification of the bacteria found in the dental plaque, and (c) study of bacteria harboring within the lesion itself. Early investigators, such as Kligler' and others,3 realized the bewildering character of the oral flora, but regarded the lactobacillus as probably a particularly significant member of the various flora. Hence, they focused their attention on the lactobacilli, usually abundant in the saliva before the appearance of clinical caries. Many others were inclined to believe that streptococci or Actinomyces play a role in caries initiation. Still, there is at present little direct evidence on which a decision could be made as to the respective importance of the organisms mentioned-and sporadic accounts of new screenings of oral bacteria4' 5on a broader scale are stimulating and promising. A fourth level has comparatively recently focused the attention of investigators.6 It is mainly the search for bacteria having the ability to invade apparently intact tooth structure in vivo, and presumably involved in initial caries, or leading its progress. MacGregor and associates" mention several investigators as stating that bacteria penetrate far ahead of actual decalcification and decay. Several distinct types of bacterial invasion of tooth structure have been repeatedly observed in histologic sections by optical and electron mieroscopy.7-9 Our investigation was carried out in two directions, with the aims in view: first, to inquire into bacterial invasion by acceptable bacteriologic criteria; and, second, to isolate the primary invaders, and to see whether they belong to a welldefined group.