Panel A is an illustration of a healthy periodontium. Note that the epithelial attachment is located at the junction of the tooth enamel and the root.
Panel B shows the changes occurring in gingivitis. Note the edema and erythema of the gingiva, and no change in bone or attachment level.
Panel C shows the loss of supporting structures that occurs in periodontitis. The gingival sulcus has deepened, creating a "periodontal pocket." Note that the attachment has moved apically and that gingiva and bone have been lost, exposing the root surface.