Bacteria are normally present in the mouth. They convert sugars and starches into acids. A combination of bacteria, acid, food, and saliva form a sticky coating on the teeth, called plaque. The acid in the plaque damages the tooth enamel, which results in the formation of a cavity.

As a cavity grows larger, the acid can reach the nerve inside the tooth and destroy it. Once this happens, the tooth dies and falls out.

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