Periodontitsis occurs when inflammation or infection of the gums (gingivitis) occurs and is not treated. Infection and inflammation spreads from the gums (gingiva) to the ligaments and bone that support the teeth. Loss of support causes the teeth to become loose and eventually fall out. Periodontitis is the primary cause of tooth loss in adults. This disorder is uncommon in young children, but it increases during the teen years.

Plaque and tartar build up at the base of the teeth. Inflammation from this buildup causes a "pocket," or gap, to form between the gums and the teeth. This pocket then fills with plaque and tartar. Soft tissue swelling traps the plaque in the pocket. Continued inflammation leads to damage of the tissues and bone surrounding the tooth. Because plaque contains bacteria, infection is likely, and a tooth abscess may also develop. This also increases the rate of bone destruction.