You may ask how can a tooth survive in the body when it's dead.  It is true that root canal therapy involves removing the tissue from within the roots, but it does not "kill" the tooth.  The tooth is still connected to the bone by a ligament, called the periodontal ligament.  That ligament is rich in blood and nerve supply and continues to provide the tooth with a tactile sense (proprioception) even after root canal treatment.  A true "dead" tooth would be rejected by the body.