The first thing that you need to know about tooth decay is that you need not let it happen to you! Tooth decay can be prevented to a very great degree if a person just understands and practices a very few basic concepts of preventative dental health.
Tooth decay is caused by acids, acids that are created by certain types of bacteria that live in our mouths. To go back a bit further, tooth decay can actually be thought of as being caused by sugar, but maybe not in the way that you would think! You see, bacteria, which are living organisms just like you and me, live in our mouths and just wait for us to consume something containing sugar, their favorite food. After these bacteria eat the sugar they, just like us, excrete their waste products, and that is what causes the acid which, in turn, causes tooth decay. You see, to put it bluntly, tooth decay is caused by bacteria poop. (Makes you think twice about eating that candy bar doesn’t it?)
Many foods contain sugar including soda, candy, milk, and even fruits and vegetables or the juices made from them. To avoid tooth decay you would need to either eliminate sugar all together or maybe set up a port-o-potty for your bacteria somewhere inconspicuous in your mouth. All kidding aside, the idea is to have these acids in your mouth and on your teeth for as short a time as possible. So, regular brushing is a must, especially after consuming any foods containing sugar!
Otherwise, you need to see your nearest dentist immediately.