Why you need them:
If a tooth's pulp, which contains blood vessels and nerves, becomes infected because of decay or injury, root-canal treatment is often the only way to save your tooth and repair the damage. Usually, this type of treatment is performed in 1-3 visits, depending upon the pulp's condition. If the tooth is abscessed (the pulp has died and infection has entered the bone), the infection may have to be drained before the root can be filled.
The material used to fill the root canal will probably last a lifetime, but eventually the filling or crown may need to be replaced. (About ten percent of root canals will fail and need to be retreated or extracted.)
After the tooth is numbed, the dentists makes an opening in it to reach the pulp chamber. The infected pulp is removed, and the chamber and the root(s) are cleaned out, enlarged, and then shaped.
Once clean and free of infection, the pulp chamber and the root canal(s) are filled with a rubber-like material.
The tooth usually will need a crown as well. Some crowns may need a post and core for additional support.