Tooth decay is an infection caused by bacteria in your mouth. When you eat, you are feeding the bacteria. As they consume carbohydrates, they are producing an acid that will make a little hole in your tooth. Once there is a hole, there is a new home for the bacteria to live. You can't get to it with toothbrush, so the hole just keeps getting bigger and bigger until it gets to the nerve of the tooth. That's going to hurt. Tooth decay does not go away by itself. It has to be taken out and replaced with some sort of filling material or covered up with a crown protect it.
