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ABSTRACT
The junctional epithelium is located at a strategically important interface between the gingival sulcus, populated with bacteria, and the periodontal soft and mineralized connective tissues that need protection from becoming exposed to bacteria and their products. Us unique structural and functional adaptation enables the junctional epithelium to control the constant microbiological challenge. The antimicrobial defense mechanisms of the junctional epithelium, however, do not preclude the development of gingival and periodontal lesions. The conversion of the junctional to pocket epithelium, which is regarded as a hallmark in disease initiation, has been the focus of intense research in recent years. Research has shown that the junctional epithelial cells may play a much more active role in the innate defense mechanisms than previously assumed. They synthesize a variety of molecules directly involved in the combat against bacteria and their products. In addition, they express molecules that mediate the migration of polymorphonuclear leukocytes toward the bottom of the gingival sulcus. Periodontopathogens-such as Actinobacillus actinomycetemcomitans or, in particular, Porphyromonas gingivalis-have developed sophisticated methods to perturb the structural and functional integrity of the junctional epithelium. Research has focused on the direct effects of gingipains, cysteine proteinases produced by Porphyromonas gingivalis, on junctional epithelial cells. These virulence factors may specifically degrade components of the cell-to-cell contacts. This review will focus on the unique structural organization of the junctional epithelium, on the nature and functions of the various molecules expressed by its cells, and on how gingipains may attenuate the junctional epithelium's structural and functional integrity.
KEY WORDS: junctional epithelium, tooth, implant, periodontal diseases.
(I) INTRODUCTION
The junctional epithelium is the epithelial component of the dento-gingival unit that is in contact with the tooth surface. The innermost cells of the junctional epithelium form and maintain a tight seal against the mineralized tooth surface, the so-called epithelial attachment (Schroeder and Listgarten, 1977). The junctional epithelium may be regarded as the most interesting structure of the gingiva. Its interposition between the underlying soft and mineralized connective tissues of the periodontium (i.e., gingival connective tissue, periodontal ligament, alveolar bone, and root cementum) points to its important roles in tissue homeostasis and defense against micro-organisms and their products (for reviews, see Schroeder, 1996; Schroeder and Listgarten, 1997). Unlike other appendages-such as scales of reptiles,...