Root canal therapy or endodontics is a common dental procedure that is used to clean the infected root canal of tooth.
The infection caused by bacteria living in the mouth can be a result of various damage to the tooth, e.g. decay, leaky filling or cracking. Infection often spreads to the bone around the apex of root causing an abscess.
During root canal treatment infected tissue of root canal (together with the nerve) is removed first (called trepanation), then the dentist disifencts the root canal and finally fills it with medicated filling for a 3-10 days to see if infection is fully terminated.
See this infographic to learn the steps of root canal treatment.