Microbial colonization in human periodontal disease: an illustrated tutorial on selected ultrastructural and ecologic considerations.

The oral cavity is populated by a prodigious microbial flora that exhibits a unique successional colonization of enamel and subgingival root surfaces. A wide range of oral sites provide different ecologic conditions and are, therefore, populated by different commensal microbial combinations. The sequence of microbial colonization, regardless of location within the oral cavity, commences with the acquisition of salivary and/or crevicular fluid-derived pellicle. As the process of successional colonization of the gingival crevice area proceeds uninterrupted, achieving critical mass between 10 and 21 days, gingivitis becomes evident at a clinical level. However, at a histologic level, gingivitis may be evident within 2-3 days of plaque accumulation. The inflammatory response sufficiently alters the ecological conditions so as to allow proliferation of supragingival plaque into subgingival areas. The subgingival plaque becomes progressively more Gram-negative and anaerobic in nature as the periodontal pocket deepens, leading ultimately to a chronic, progressive deterioration of the periodontium--adult periodontitis. Both gingivitis and adult periodontitis are characterized by the successive colonization of cocci, short and long rods, filamentous microbes with "corn cob" and "bristle brush" formations, flagellated microbes, and spirochetes. Localized juvenile periodontitis (LJP), in contrast to the adult form of periodontitis, features a comparatively sparse microbial flora. The subgingival microbial colonization characteristically features cocci, short rods, coccobacilli, and spirochetes.