Root canal therapy may be necessary if the pulp of the tooth is damaged.  The pulp includes the nerve and blood supply to the tooth.  This may be damaged by bacterial invasion due to caries (tooth decay), trauma that exposes the nerve such as a cracked tooth, loose or repeated fillings with recurrent decay, and occasionally from periodontal disease.  The tooth pulp becomes irritated, and this can cause pressure and pain within the tooth.  The tooth eventually dies and begins to drain necrotic tissue into the bone surrounding the tooth.  This is commonly referred to as an “abscessed tooth”.  Endodontic therapy returns your tooth to function and comfort by removing the decay or the damaged portion of the tooth, then removing the nerve and blood supply from within the canals of the teeth, treating the infection if applicable and replacing it with a material that seals the tooth from the outside environment.  The tooth is then restored with a filling or most ideally a crown to strengthen it further.  This treatment is very useful in restoring an otherwise dead tooth without having to extract it.