Figure 1. Endodontic microflora of a human tooth with apical periodontitis (GR). The areas between the upper two and the lower two arrowheads in (a) are magnified in (b) and (c), respectively. Note the dense bacterial aggregates (BA) sticking (b) to the dentinal (D) wall and also remaining suspended among neutrophilic granulocytes in the fluid phase of the root canal (c). A transmission electron microscopic view (d) of the pulpo-dentinal interface shows bacterial condensation on the surface of the dentinal wall, forming thick, layered biofilm. Magnifications: (a) 46x; (b) 600x; (c) 370x; and (d) 2350x. (From Nair, 1997.)