A root canal is needed when the pulp or nerve of a tooth gets affected by decay or trauma. The blood flow within the tooth rushes to the site of inflammation in order to aid the tooth, but what occurs as a result is a pressure on the nerve endings which generates the pain response. Pain usually occurs at night or when lying down, can be triggered by hot or cold and can be occasional or continuous. What occurs is a slow progression whereby decay may invade the pulp space and travel through the canal and settle at the end of the root. What occurs is an abscess or swelling at this site. Other causes of nerve pain can be fractures of teeth, large fillings that are not tolerated by the pulp or constant trauma to the tooth. Occasionally, it is difficult to diagnose which tooth may be the culprit until localization occurs. Treatment involves cleaning the canal space by removing the infected or affected nerve, washing the space and filling the space with an inert, rubber-like material that helps seal the space. Bio-compatible cements are used with this material to seal any smaller openings. As with any procedure, success or failure of a procedure depends on the circumstances, infection and patient. These can be discussed with the individual dentist. After endodontic therapy, the patient returns to the dentist to restore the tooth .