It may be able to be saved, but it is important to follow some basic steps to give the best chance possible. This is a really good thing to know beforehand. This can determine if a tooth can be re-attached or a more invasive procedure will be required.
First, pick up the tooth by the crown (the chewing surface). NOT the root! You are going to want to limit contact with the root as best you can. If the tooth is dirty, gently wash it with water. Now re position the tooth in the socket as immediately as you can. If the tooth was knocked all the way out, there will be damage beyond just the tooth.
Be sure to keep the tooth moist at all times.
If it is not possible to replace the tooth in it's socket, then how you store the tooth is also important.
Keep it in a clean container of milk, saltwater or saliva. You do not want to wrap it in a napkin or allow it to become dry. Allowing it to become dry reduces the chance that it will reattach.
When a tooth has is knocked out, the nerves, blood vessels, and supporting tissues are damaged, too. The nerves and blood vessels can't be repaired. That is why all avulsed teeth will need a root canal. However, the bone can reattach to the root of the tooth once it's put back into place.
A missing permanent tooth is a large concern about appearance. Even though a knocked out tooth can cause concerns, it is not the dire situation that you might imagine. The National Association of Endodontists reports that 5 million teeth are knocked out each year, so dental professionals have experience handling the unexpected challenges associated with an injury or an accident.
See an endodontist or dentist within 30 minutes of the injury. A gap might cause concerns about your smile, but you do have options if your tooth is knocked out.