What is tooth enamel chemically? State the condition when its starts corroding?

What is tooth enamel chemically? State the condition when its starts corroding?
What happens when food particles left in the mouth after eating degrade?
Why do doctors suggest use of tooth powder/tooth paste to prevent tooth decay?

White tooth enamel is calcium phosphate which is very hard. It gets affected when the pH of our mouth falls below 5.5. The bacteria present in our mouth breaks down the food particles into acids which damage our teeth by corroding them.

To prevent the tooth decay, cleaning of the mouth thoroughly after eating with tooth powder/paste, which is basic in nature and neutralizes the excess of acid, is a must.