Cavities starts with bacteria...
Thousands of bacteria live in your mouth, and most of them are beneficial. But a few are harmful, including the streptococcus mutans bacterium, the one responsibile for tooth decay. These bacteria thrive in plaque, a sticky film that's constantly forming on your teeth.
Add starches, and the process begins
The S. mutans bacteria feast on starches in your mouth, then produce an acid that dissolves your tooth enamel, until eventually you have a hole on the surface of your tooth (a cavity). The only way to stop the decay process is for us to remove the decay and put in a filling material.
The good news...
When you brush and floss properly, you are removing the plaque from your teeth, leaving little for bacteria to eat. As a result, their growth is slowed, and they don't produce the acids that lead to tooth decay. This is why it's important to remove plaque from your teeth each day.