A cavity is a small hole that forms on the tooth

A cavity is a small hole that forms on the tooth surface when the sugar mix that contain food and bacteria that are in the mouth.

The merger of sugar and bacteria produces a mild acid that can tackle the tough outer layer of teeth, called enamel. Cavities are more common in children. But adults can also be affected. Mostly on the 2 categories in adults:

Caries "recurring" - Cavities are formed around a filling. The surface of a tooth restored is not as smooth as that of a natural tooth. Small food particles and bacteria may remain stuck at the edge of the shutter, thus promoting the formation of a new cavities. In addition, the exposed part of a tooth filling which is broken is more susceptible to cavities.
Caries "root" - the cavities that form the roots of teeth. Years of brushing too hard, even aging may push back the gums, exposing the roots. The latter have no enamel to protect them and are therefore more susceptible to cavities.