Subgingival biofilm formation

The human body contains numerous distinctive ecosystems that provide a unique environment for colonizing microorganisms. The periodontal pocket is one such microniche. This environment is partially sheltered from the physical shear forces in the oral cavity and contains the hard, nonshedding surfaces of the tooth root along with the shedding surfaces of gingival mucosa. The junctional epithelium, which is attached to the tooth root, is poorly differentiated, lacks keratinization and has relatively wide intercellular spaces. Consequently, junctional epithelium is permeable and allows the migration of polymorphonuclear leukocytes into the periodontal pocket. Furthermore, the tissues in the periodontal pocket are bathed in gingival crevicular fluid, a serum exudate with antioxidant properties. The initial bacterial colonizers attach to the available surfaces, as discussed elsewhere in this volume of Periodontology 2000. Later colonizers attach to the antecedent organisms and assemble into polymicrobial communities. The biofilms on the hard surfaces develop into spatially organized structures that can extend several hundred micrometers from the surface. By contrast, the epithelial surfaces, which are continually being sloughed and replenished, tend to be colonized with monolayers of microorganisms. However, several of the more pathogenic species of bacteria are able to invade the gingival cells and tissues where they can remain viable and thus constitute a nidus of infection.