Figure 2. Well-entrenched biofilm at the apical foramen of a tooth affected with apical periodontitis (GR). The apical delta in (a) is magnified in (b). The canal ramifications on the left and right in (b) are magnified in (c) and (d), respectively. Note the strategic location of the bacterial clusters (BA) at the apical foramina. The bacterial mass appears to be held back by a wall of neutrophilic granulocytes (NG). Obviously, any surgical and/or microbial sampling procedures of the periapical tissue would contaminate the sample with the intraradicular flora. EP, epithelium. Magnifications: (a) 20x, (b) 65x, and (c,d) 350x. (From Nair, 2002.)