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The simplest form of gingivitis is associated with the accumulation of supragingival plaque along the gingival margins of the teeth. This form of gingivitis has been extensively studied in human volunteers, and the sequence of events is well described. In these studies, individuals are brought to a state of health and then refrain from all forms of oral hygiene for a 3- to 4-week period. The initial colonizers of the teeth are streptococci, which proliferate and in turn become colonized by other bacteria present in saliva, such as various Actinomyces species and Veillonella. The greatest growth of the plaque occurs at the gingival margin, where plaque accumulations usually are visible after several days. This plaque may, in some instances, provoke a bleeding gingivitis in which spirochetes and Actinomyces viscosus are prominent members of the plaque flora. If this plaque remains undisturbed, the flora gradually shifts toward an anaerobic, Gram-negative flora that includes black pigmented bacteroides and several types of spirochetes. The increase in these anaerobic organisms can be explained by the low oxidation-reduction potential of the aged plaque and by nutrients derived from the inflammatory exudate at the site.
The gingivitis may resolve itself or fester subclinically for an indeterminate period; however, the potential for the formation of a periodontal pocket (periodontitis) exists at any time. When pockets are detected clinically, they usually are associated with calcified plaque deposits, called calculus, present on the tooth surfaces. For many years, calculus was thought to be the etiologic agent of periodontitis, because inflammation usually subsided when it was removed and the tooth surfaces were mechanically cleaned. However, calculus is always covered by plaque, and removal of calculus would be synonymous with debridement of plaque. The subgingival plaque flora associated with periodontitis is dominated by an anaerobic, Gram-negative flora in all cases but one, and that is a unique clinical entity formerly known as periodontosis, and now as localized juvenile periodontitis (LJP). LJP is an important clinical entity because of the understanding it has provided of the complex and dynamic interactions between the host and the flora in the pocket ecosystem.
