The best prevention of knocked-out (avulsed) teeth is the use of helmets and mouthguards!

Baby Tooth

• It is NOT recommended to replant avulsed primary teeth, as this can damage the developing adult tooth under the gum.
• Make an appointment with your dentist as soon as possible. At the initial examination, your dentist will make sure that all teeth are accounted for. If not, it is highly recommended to make a radiographic examination in order to ensure that the missing tooth is not a case of complete intrusion (pushed inside the bone) or root fracture with loss of the coronal fragment.
• Maintain a soft diet for 1 week and ensure good oral hygiene. Your child will need to be reviewed regularly to ensure the normal development of adult teeth.

Adult tooth

Dental avulsion is a real dental emergency in which prompt management (within 20–40 minutes of injury) affects the prognosis of the tooth.

• Keep the patient calm.
• Find the tooth and pick it up by the crown (the white part). DO NOT touch the root of the tooth as this will compromise the prognosis of the tooth.
• If the tooth is dirty, wash it briefly (10 seconds) under cold running water and reposition it. Try to replant the tooth if possible. Bite on a handkerchief to hold it in position.
• If this is not possible, place the tooth in a suitable storage medium, e.g. a glass of cow’s milk (on ice if possible) or a special storage medium for avulsed teeth if available (e.g. Hanks balanced storage medium or saline). Avoid storage in water!
• The tooth can also be transported in the mouth, keeping it between the back teeth and the inside of the cheek. If the patient is young, they could swallow the tooth. It may be advisable to get the patient to spit in a container and place the tooth in it.
• Seek emergency dental treatment immediately. Your dentist will assess the teeth and soft tissue. Once replanted into the correct position, the tooth is splinted into place for a minimum of 7-10 days. Lip or gum lacerations may require stitches. X-rays will be required to check for additional injuries and the position of the tooth.
• Maintain a soft diet, antibacterial mouthwash and gentle but thorough oral hygiene for 2 weeks.
• Systemic antibiotics or a tetanus injection may be required.

Regular review appointments will be required to remove the splint, monitor the vitality of the tooth or continue root canal treatment that may have commenced at the initial appointment.

Link: http://www.dentaltraumaguide.org/permanent_avulsion_treatment.aspx