A root canal is necessary when decay or trauma affects the pulp or nerve of a tooth. The blood flow in the tooth rushes to the site of inflammation to aid the tooth. What actually occurs is a pressure on the nerve endings, generating pain, which usually occurs at night or when lying down, and can be triggered by hot or cold. What occurs is a slow progression of decay travelling through the canal and settling at the end of the root. This results in an abscess (or swelling) at this site. Other causes of nerve pain can be tooth fractures, excessively large fillings, or constant trauma to the tooth. Occasionally, it is difficult to diagnose which tooth may be the culprit. Treatment involves cleaning the canal space by removing the affected nerve, washing the space and filling the space with an inert, rubber-like material that helps seal the space. Biocompatible cements are used with this material to seal any smaller openings.