Definition of Broken or knocked out tooth:

The dentist's term for a knocked out tooth is "avulsed."

Considerations:

A permanent tooth that is knocked out can sometimes be reimplanted. In most cases, only permanent, adult teeth are reimplanted into the mouth. Baby teeth are usually left out. 

Immediately contact your dentist when a tooth is broken or knocked out. If you can find the tooth after the accident or injury, bring it with you when you seek medical help.

Causes:

Tooth accidents are commonly caused by:

• Accidental falls
• Sports-related trauma
• Fighting
• Car accidents
• Biting on hard food