Periodontal disease (gum disease) is an infection of the tissues that support the teeth.Periodontal diseases attack just below the gum line in the sulcus (a very shallow “V”-shaped crevice between the tooth and gums), where they cause the attachment of the tooth and its supporting tissues to break down. As the tissues are damaged, the sulcus develops into a pocket: generally, the more severe the disease, the greater the depth of the pocket. Gum diseases are classified according to the severity of the disease. The two major stages are gingivitis and periodontitis. Gingivitis is a milder and reversible form of periodontal disease that only affects the gums. Gingivitis may lead to more serious, destructive forms of periodontal disease called periodontitis.