Reasons for root canal therapy
Root canal treatment (endodontic therapy) is called for when decay or a fracture has exposed the tooth pulp (nerve) to bacteria in the mouth. An infections results and pus is generated in the pulp chamber. Left untreated, the infection will spread to the bone around the tooth.
In the beginning there may be little or no pain involved with this condition. It is when the infection reached the pulp (nerve and blood supply) that the pressure builds and that is when the pain can become severe.