Light and electron microscopic studies of root canal flora and periapical lesions

  • Author Footnotes
    1 Dr. Nair is affiliated with the Department of Oral Structural Biology, Dental Institute, University of Zurich, Zurich, Switzerland.
    P.N. Ramachandran Nair
    1 Dr. Nair is affiliated with the Department of Oral Structural Biology, Dental Institute, University of Zurich, Zurich, Switzerland.
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  • Author Footnotes
    1 Dr. Nair is affiliated with the Department of Oral Structural Biology, Dental Institute, University of Zurich, Zurich, Switzerland.
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      This study elaborates on (a) the structure of the root canal flora in periapically affected human teeth; (b) the relationship of flora to the dentinal wall of the root canal; (c) morphological aspects of interaction among diverse groups of bacteria; and (d) the dynamic nature of inflammatory host response at the periapex. Spontaneous human periapical lesions (30 granulomas and 1 radicular cyst) obtained by tooth extraction were processed for light and electron microscopy. All 31 teeth showed bacteria in their root canals. The flora consisted of cocci, rods, filamentous organisms, and spirochetes. The rods often revealed Gram-negative walls. The bacterial flora formed clusters of “self-aggregating” colonies of one distinct type or “coaggregating” communities of several types. Electron microscopically a condensed bacterial layer could be identified on the dentinal wall of the root canal which when light microscopically visible, gave the palisade structure of bacterial plaques adhering to tooth surfaces. The endodontic flora was separated from the rest of the lesion by a dense wall of neutrophils (PMN's) or by an “epithelial plug” at the apical foramen. Five specimens revealed both intra- and extracellular bacteria within the body of the lesions. The membrane-delimited phagosomes containing bacteria showed interaction between phagocytic cells and bacteria. The presence of the “immunocoating” on the surface of certain phagocytosed bacteria strongly suggests that they were not contaminants but actual tissue invaders against which the host mounted a specific immune response at the periapex.
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