Teeth can easily decay because germs readily grow on bits of food that tend to stick of the teeth after a meal . The germs break down food particles to produce acids. The acids wear away the enamel and dentine of a tooth to expose the nerves and blood vessels in the pulp cavity . The tooth begins to ache and the gum becomes infected. Finally the tooth falls off .once a permanent tooth falls off it cannot be replaced by another tooth. Therefore it is very important to take care of our teeth