An immunohistochemical study of the relationship between periodontopathogens and focal infection

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It is speculated that focal infection of oral origin may derive from periodontal pockets and periapical lesions. Porphyromonas gingivalis is believed to closely associated with adult periodontitis. It was recently reported that P. gingivalis was isolated from periapical lesions. In this study, we determined the ability of combination of periodontopathogenic microorganisms to cause tissue destruction in a murine abscess model. Although all bacterial combinations used in this study produced larger abscess than did monoinfection of each bacterium, the combination of P. gingivalis and B. forsythus showed a synergistic effect on an abscess formation. Since these two bacteria have been frequently found together in lesions of periodontitis, it has been suggested that the significance of their co-infection in the progression of periodontitis. On the other hand, the combination of P. gingivalis and a mixed flora of bacteria within the root canal enhanced bone destruction around the root apex, and progressed the expansion of submaxillary lymph nodes in a rat model system of apical periodontitis. During the bone resorption phase, numerous macrophages expressing IL-1β were observed adjacent to many osteoclasts that contained large cytoplasms. On the contrary, after the application of an antibacterial agent (ofloxacin) to experimentally induced periapical lesions, a significant increase of macrophages expressing TGF-β1 and extensive bone formation was seen in the periapical lesions. These results suggest that mixed infection of P. gingivalis and the intra-root canal bacteria may be involved in progression of apical periodontitis, and macrophages expressing TGF-β1 may play an important role in the activation of new bone formation during the healing process of apical periodontitis.