Bacteria are normally present in the mouth. They convert sugars and starches into acids. Plaque forms when the bacteria and acids mix with food and saliva. The acid in the plaque can damage the tooth enamel, which results in the formation of a cavity. As a cavity grows larger, the acid can destroy the tooth.

Plaque can crystallize to form a very hard coating, called tartar. Plaque and tartar can also cause gingivitis, dental abscesses and periodontal disease.