In the event you or a loved one knocks out a tooth because of some type of trauma, there are some things you should do right away. If the tooth has been avulsed completely and the root is not fractured, keep it moist. The cells on the root of the tooth should not be allowed to dry out or they will die. Dead cells on the surface of a tooth preclude it from being re-implanted into the socket.
It was once common to suggest placing the tooth in milk until a dentist could be consulted, and doing so is far preferable to allowing the tooth to dry out. However, milk is not readily available all the time and using such introduces foreign proteins, fats, milk sugars and the like onto the root surface. Commercially prepared kits to preserve knocked out teeth are available and any good sports medicine first aid kit should contain such. If, however, nothing is available, place the tooth into the cheek so saliva can continue to moisten and bathe the tooth. Better yet, if the root is not visibly dirty, try returning the tooth to the socket itself, that is if the socket is not distorted or crushed and it is not too painful.
You should contact your dentist for a tooth avulsion immediately so that the tooth may be returned to the socket and stabilized in some manner. Often, such teeth will reattached into the socket and continue to serve the patient. Avulsed teeth, however, have had their blood supply to the inner pulp broken, and as such, the inner soft pulp of the tooth will die. An avulsed tooth that is re-implanted into the jaw must have root canal or endodontic therapy completed on it. Typically this will be done once the tooth is stabilized for a time and the attachment reforms. Some dentists will perform endodontic therapy on a tooth while outside of the mouth--keeping it moist all the while--and then return the tooth to the mouth.
It is important that when a tooth is re-implanted, that the tooth itself is stabilized in such a fashion that it has just a slight amount of movement to it or the tooth is more likely to ankylose--or become one with the bone. Often this means some wiring of the arch or even some orthodontic brackets.
Timely and proper treatment for a tooth avulsion is important to long-term success in retaining the tooth. While there is no guarantee than a tooth can be saved, once its knocked out, good success with re-implantation of teeth is common if the knocked out tooth is treated correctly and prompt re-implantation and stabilization is done.