Root canal treatment (also referred to as root canal therapy or endodontic therapy) is necessary when a cavity irreversibly injures the pulp (nerve) of the tooth. Sometimes deep restorations or trauma to a tooth may also cause the nerve to be damaged to the point that it needs root canal therapy. Once this occurs the pulp becomes infected, and can even extend through the root tip and begin to eat away at the surrounding bone (this is an abscess). By the time the pulp is infected it must be treated, and cannot heal on its own. It can even weaken the entire immune system. This is dangerous, not to mention very painful. Symptoms that the pulp has become infected may include sensitivity to hot/cold or sweets, pain, bump on the gum, swelling, pain to biting or pressure, and a bad taste in the mouth. Sometimes, however, no symptoms are apparent and the person is unaware of any problem until a checkup.

A procedure is then performed to clean out the infected tooth pulp and soft tissue, and disinfect the canals of the tooth. The only alternative would be to remove the tooth. Once the infection is resolved, the canal(s) are filled in to prevent any further infection. Usually a core build-up (filling) and crown is recommended for restoring a tooth that has had root canal therapy, this provides proper support to the tooth structure.