Light and electron microscopic observations of osteoclastic alveolar bone resorption in rats monoinfected with Actinomyces naeslundii.

Alveolar bone destruction in rats monoinfected with Actinomyces naeslundii proceeds via osteoclastic resorption. The osteoclastic activity is discontinuous, i.e. short periods of vigorous osteoclastic activity are followed by longer periods of inactivity during which the alveolar crest may be covered with osteoblastic cells or in many cases devoid of bone cells. The net effect in the monoinfected rats is rapid bone loss. Periods of osteoclastic activity were associated with dense inflammatory infiltration of the interdental tissue, ulceration of col epithelium and the presence of large adherent plaques of Actinomyces. Ultrastructural examination revealed uninuclear as well as multinuclear osteoclasts. These cells contained numerous mitochondria, abundant Golgi apparatuses, and well developed ruffled borders indicating that they were physiologically active in bone resorption.