Root canal treatment is necessary when the nerve and blood supply to the tooth becomes infected.  If an infected tooth is left alone for a long period of time an abscess can develop.   Symptoms that the pulp has become infected may include sensitivity to hot/cold, lingering pain, swelling, and pain to biting or pressure.

Treatment is then performed to clean out the infected pulp tissue, disinfect the canals of the tooth, and fill the canals with an inert material.  Now that the tooth is free from infection, a definitive restoration can be placed, most likely a full coverage crown.