Formation of cavities is a breakdown of teeth due to the formation of by bacteria after food decay ........

Explanation:

The cause of caries is acid from bacteria dissolving the hard tissues of the teeth (enamel, dentin and cementum).
The acid is produced by the bacteria when they breakdown food debris or sugar on the tooth surface.

Simple sugars in food are these bacteria's primary energy source and thus a diet high in simple sugar is a risk factor.
If mineral breakdown is greater than build up from sources such as saliva, caries results