Cavities are small holes that slowly develop in the teeth because of tooth decay.

Tooth decay usually happens slowly over a period of months or years. Acids made by plaque eat away at the hard (mineral) part of the tooth. Sometimes the tooth can use minerals in saliva to rebuild itself. A cavity forms when the damage caused by acids is more than the tooth can repair.

Mild tooth decay may be helped by effective tooth-brushing and flossing, as well as daily rinsing with fluoride mouth care products. More serious tooth decay that has caused cavities may require fillings to stop the decay and prevent further damage to the teeth.

Infants who are put to bed with a bottle or who are allowed to suck on a bottle with any sugar-containing substance (such as juice) for a long time may develop cavities, especially in the upper front teeth. This condition is called "baby bottle tooth decay." Children who have cavities in several teeth (usually the upper front teeth) may have trouble chewing hard foods and learning to speak, due to pain and tooth damage. Cavities in infants can often be prevented by making sure the baby's mouth and teeth are cleaned after the last feeding at night.