Periodontal diseases can be broadly classified as diseases of the tissues surrounding a tooth, which are the gingiva, periodontal ligament, and alveolar bone (fig. 1). There are two main types of periodontal diseases: (1) gingivitis, or inflammation of the gingiva surrounding a tooth (fig. 2 is Normal and figs. 3–6 are gingivitis), and (2) periodontitis, or inflammation of the deeper supporting tissue of the tooth (periodontal ligament and bone) (figs. 7–11). In periodontitis, the inflammation leads progressively to irreversible loss of tissue support of the affected teeth.

Gingivitis and milder forms of chronic periodontitis are common in adults. Chronic periodontitis often begins in adolescence, but is usually not clinically significant until the mid-30s. Chronic periodontitis is strongly associated with tobacco use. Other factors, such as increasing age, infrequent dental visits, low education level, low income, diabetes, and immuosuppression are also associated with an increased risk of developing periodontitis.