Root canal treatments are required when there is some form of trauma or infection to the nerve and blood vessels (pulp tissue) within the tooth itself. You may experience extreme pain or sensitivity, along with a darkening of the tooth. If the infection has progressed significantly, you may also get an abscess in the gums near the suspected tooth.
The treatment involves removing the infected tissues, cleaning out and disinfecting the internal structure of the tooth, then finally placing a root filling to seal the canals to prevent future infections.