Tooth decay, which is also called dental caries, is the destruction of the outer surface of a tooth (enamel) followed by the destruction of the inner body of a tooth (dentine).

Decay results from the action of bacteria that live in plaque, which is a sticky, whitish film formed by a protein in saliva and sugary substances in the mouth. The plaque bacteria sticking to tooth enamel use the sugar and starch from food particles in the mouth to produce acid.