The tooth will need to be re-implanted into its socket immediately so contact your dentist. In the meantime, hold the tooth by the crown and rinse off the root of the tooth in water if it’s dirty. Do not scrub it or remove any attached tissue fragments. If possible, gently insert and hold the tooth in its socket. If that isn’t possible, put the tooth in a cup of milk and take it with you to your dentist as quickly as possible.