Root canal treatment (also called endodontic therapy) is necessary when a cavity is allowed, through neglect, to reach all the way to the nerve inside the tooth. Sometimes deep restorations or trauma to a tooth may cause the nerve to be damaged and pain and infection can result. When the nerve is infected, it must be treated; it cannot heal on its own. While symptoms can include sensitivity to hot/cold or sweets, pain, swelling, pain to biting or pressure, and a bad taste in the mouth, sometimes no symptoms are present and the patient is unaware of the problem until the dental exam.
A root canal is performed to clean out the infected tooth pulp, and disinfect the canals of the tooth. The only other treatment would be to extract the tooth. Once the infection is resolved, the canal(s) are filled in to prevent any further infection. Usually a core build-up and crown is recommended for restoring the tooth to prevent it from breaking in the future.