Injury to the dental pulp (nerve) can lead to pulp infection and/or its death. Root Canal Therapy must be performed in order to avoid the spread of infection to the surrounding root tissues and avoid the loss of the tooth. The treatment involves removing the nerve, filing the canals to a uniform shape and then completed by filling the canals with a material called gutta percha. This is usually a two appointment procedure, but can require more if canals are difficult to find or re-infection occurs. If the pulp dies without infection, your dentist may decide that the entire procedure be completed in one appointment.
Once a tooth has under gone RCT it no longer has a blood supply and becomes brittle, therefore prone to fracture. It is usually recommended to get a crown to surround the tooth and prevent it from splitting like firewood, vertically into the gums/bone. If this happens, the tooth is now non-restorable and usually has to be extracted.
The general public has the notion that Root Canal Therapy is experiencing pain; but in most cases the patient falls asleep during the procedure.