Pulp refers to the softest part of the tooth that lies in its root and extends all of the way to the top part of the tooth (the crown). The pulp contains the blood vessels the nerves and connective tissue inside a tooth and provides the tooth's blood and nutrients. It is essentially the lifeline to the tooth and there is a branch of dentistry endodontics which specializes in its treatment.
If the pulp of a tooth becomes damaged beyond repair it essentially means that the tooth has died. Damage to the pulp can be a result of a cracked tooth or a deep cavity. In the case of deep cavities bacteria inside the mouth will become exposed to the dental pulp which causes infection. This damage will become visible if an abscess (a pocket of pus forms at the tip of the tooth root) develops and will require endodontic treatment.
The most effective treatment of abscess is root canal therapy in which the tooth is saved by cleaning out and filling the damaged pulp. In this procedure the infected pulp must be removed from the pulp chamber and the root canals. The pulp chamber and root canals are then thoroughly cleaned and enlarged after the infected pulp is removed. A filling is then attached in order to prevent bacteria from entering the root canals and pulp chamber areas. A crown is placed over the tooth in order to retain the original shape of the tooth.
If the abscess is not treated it can lead to the deterioration of the bone holding the tooth. Depending on the severity of the bone deterioration the tooth can fall out. Therefore it is recommended that on cases where the pulp and therefore the tooth cannot be saved tooth replacement should be sought.