Root canal treatment (or endodontic therapy) is made necessary when an untreated cavity reaches all the way to this pulp. Treatment may also be needed when deep restorations or trauma to a tooth cause nerve damage. Once the pulp becomes infected, it can begin to eat away at the surrounding bone (this is known as an abscess). If the pulp is infected, not only is it painful but it will require treatment as it cannot heal on its own.
Symptoms that indicate the pulp has become infected may include sensitivity to hot/cold or sweets, pain, swelling, pain to biting or pressure, and a bad taste in the mouth. However, sometimes no symptoms are apparent and you may be unaware of any problem until a checkup.
A root canal is performed to clean out the infected tooth pulp and disinfect the canals of the tooth. Alternate treatment would be to extract the tooth. Once the infection is resolved, the canal is filled in to prevent any further infection. Usually a core build-up and crown is recommended for restoring a tooth that has undergone root canal therapy.