Root canal therapy (RCT) is a technique used to retain a tooth with an irreversibly damaged nerve, so that it can be saved and remain functional in the mouth. Nerve damage is usually caused by bacterial invasion of the pulp due to decay, resulting in an infection that spreads through the root canal system of the tooth, eventually leading to an abscess. The aim of the treatment is to remove all infection from the root canal, then clean and fill the root canal system. Once all the infection has cleared, the tooth is permanently restored, and may require a crown to provide extra strength to the weak remaining tooth structure. This tooth is then examined and reviewed at regular check ups to ensure its integrity is intact.