Root canal treatment falls into a field of dentistry called endodontics, which deals with the nerve, or sensitive inner portion of the tooth. Root canal treatments, and other related procedures, have helped millions of patients overcome poor tooth health, and have reduced painful problems.
If the tooth does not have an active infection, it should not hurt. With modern anaesthesia, painless root canals are not a myth anymore. However, teeth that require a root canals are not always painful. Sometimes, teeth may be dead for months or years, and may not cause pain at all. Only when they get infected and cause a considerable amount of damage in the tooth and in the bone holding them, will they cause pain. If a root canal is done at the right time, before it starts causing pain, the prognosis of the tooth is always better.
Moreover, the strengthening of the tooth after the procedure with fillings and crowns/bridges is important as dead (root canal teeth) are more brittle than living teeth. Placing a crown/bridge on the tooth is the general recommendation for teeth that have had root canal therapy.