Root canal therapy can save a tooth whose pulp is diseased or damaged. The pulp is the internal part of the tooth that contains the nerves and blood supply. Pulp problems occur when the crown of the tooth is decayed or injured so that the pulp is exposed. The pulp becomes infected when bacteria enter the pulp. The infection can then spread throughout the pulp into the roots. When this happens, an abscess (a pocket of pus) may form. Left untreated, the infection can cause bone loss and tooth loss. The purpose of a root canal is to stop the infection by removing dead or dying tissue, so that the tooth can be saved. Because a root canal filled tooth becomes somewhat brittle, a crown is often recommended to protect the tooth from breakage.