The Microbic Flora of the Dental Plaque in Relation to the Beginning of Caries

Abstract

The bacterial flora of the oral cavity is one of the most complex to be found in or on the human body. This may be attributed in part, at least, to the variety of environments which may be found in the mouth and to the constant inflow of microorganisms from the air and food. This rich field of investigation has intrigued many workers since the early work of W. D. Miller (1) and a very diverse literature has accumulated. Numerous contributions have dealt with the microorganisms indigenous to the mouth and with changes in the flora related to specific diseased conditions. Most of the reports have been restricted to some part of the flora, usually to a single genus or species. Among those studies having a less specialized viewpoint and making notable contributions to knowledge in this field should be included the work of Kligler on the relationship of bacteria to dental caries (2), of Bloomfield (3) and of Brailovsky-Lounkevitch (4) on the evolution of the oral flora in infants, of Howitt and Fleming on changes in the flora associated with different diets (5) and of Bibby (6) and of Brooke (7) on smears from different areas in the mouth. Little attention has been given by workers in either dental or bacteriological fields to the microbic flora of the dental plaque, in spite of the frequently repeated observation, first made by G. V. Black, that in the earlier stages of the carious process the lesion is always found beneath a plaque composed of bacteria and other microorganisms. These masses are most often found on tooth surfaces which are protected from the normal cleansing mechanisms of the oral cavity and in areas difficult to reach with ordinary dental instruments. The paucity of information in this field of dental research is also partly attributable to the numerous technical difficulties of sampling and cultivation of the small amounts of material available. It seems apparent, however, that a search for the bacterial agent or agents which may be responsible for the earliest stages of the carious process must be made among those microorganisms in and under the plaque. If decay is initiated by local bacterial action the responsible microorganism should be found in plaques covering carious enamel and, conversely, if the relationship is a direct one, should be absent when the surface is found to be caries inactive. Indirect evidence of differences in bacterial flora between caries active and caries free tooth surfaces is found in the work of Stephan (8). He has shown that the pH