Periodontal disease is a general term encompassing several non-tumoral diseases of the periodontium. Some periodontopathies are considered the periodontal manifestation of systemic diseases, e.g. so-called desquamative gingivitis, primary herpetic gingivostomatitis, hormonally mediated changes like "pregnancy gingivitis," and some others related to metabolic disturbances, e.g. diabetes mellitus. Drug-associated gingival inflammation, e.g. hydantoin-induced hyperplasia, and rapid onset infections possibly associated to psychosomatic distress like acute necrotizing ulcerative gingivitis (ANUG), are also included. However, the most common periodontal diseases are infectious in origine, initiated by proinflammatory substances derived from the microbial dental plaque accumulating at or near the neck portion of the teeth or crevicular sulcus of the gingiva. There are several classifications of periodontal disease which consider clinical, bacterial, host, and environmental factors. The classification used in this work 'is generally in accordance to that elaborated by Page and Schroeder (42) and the committee of Deutsche Gesellschaft fiir Parodontologie (13). Periodontal disorders induced by bacteria and named gingivitis and periodontitis, have been considered a group of local infections (39). More than 300 species of bacteria are currently recognized in the oral cavity which may vary interindividually or from site to site on different teeth of the same person. However, only a few species are proven to participate predominantly in the infectious process and have been constantly found in association to certain forms of periodontal disease (30, 39).