This diagram demonstrates two fixed treatment modalities that can be used to replace a single missing tooth.  Replacement with a bridge is reasonable if the two teeth next to the missing tooth space are structually compromised and would require a crown restoration, or if placement of a dental implant is not possible or would require extensive bone or gum grafting.  If the teeth next to the missing tooth space are structually stable, then replacement with a single tooth implant and crown is the best option.