How do my teeth know when to fall out?

Each tooth is held in place by roots. Roots sort of look like strings. Roots attach to your jawbone at one end, and your tooth on the other. They hold your baby tooth in place until your permanent tooth starts to grown in. The permanent tooth dissolves the root of the baby tooth. "Dissolves" means the root starts to disappear. As the root disappears, the baby tooth gets loose. The tooth soon falls out.

Are babies born with teeth?
Will my baby sister ever get any teeth?
Mom says my baby brother is teething. What's that?
How many teeth do I have?
Why do baby teeth fall out?