If you are talking about your adult teeth once it falls out you can not put it back in and new one will not grow in its place. You will need a replacement either a implant or bridge. The bridge would be the cheaper choice. As the name bridge sounds you need to have teeth on either side of the gap. Bridges are not removable. A implant is cost more and also not removable, however you do not need teeth on either side of the gap.
Either way you need to fill the gap other wise your remaining teeth may shift.