Bacterial invasion of the periodontium; an important factor in the pathogenesis of periodontitis?

Tissue samples from 2 humans suffering from severe periodontitis were investigated by transmission electron microscopy. Confirming earlier observations in gnotobiotic rats, bacteria were found in various regions of gingival tissues. We observed bacteria invading the pocket epithelium, the underlying connective tissue, and microorganisms were also present deep in the connective tissue. The bacterial invasion of the periodontium was accompanied by different stages of tissue degradation. Various morphologically distinct types of Gram-negative and Gram-positive bacteria were evident. These microorganisms were found in the apical part of the periodontium. More coronally, a heavy infiltrate consisting predominantly of plasma cells was present. It is suggested that bacteria cannot invade regions of connective tissue protected by a massive cellular infiltrate. It seems that they rather circumvent this strong defense by penetrating more apically through the pocket epithelium while producing as camouflage leukochemophobic compounds which paralyze the chemotactically regulated mobile defense. It seems to us that bacterial invasion is a consistent feature of advanced periodontitis, leading to focal necrosis or microabscesses, and may well explain the cyclic nature of this disease.