Root canal treatment is done when the nerve in the tooth is inflamed with infection (irreversible pulpitis) or has died (necrotic).
Root canals are also done when a tooth is cracked prior to placing a crown. If the crack is severe, the tooth is deemed hopeless and it is taken out (extracted).
As well, root canals are done if there is trauma or if there is a fracture involving the nerve system. If left untreated, this can become painful and can also become infected and/or swollen (abscess).
During a root canal, the entire root system is cleaned and disinfected through an access hole made in the top of the tooth. The root system is then sealed with gutta percha (a natural rubber material). The access hole is then filled and most often a crown (cap) is placed to protect the tooth.