If the nerve in the root-canaled tooth is gone, how can I feel pain from that tooth?

As endodontists, we get this question a lot.  To answer it, we need to chat a little about… the anatomy of a tooth:  There are two basic types of nerves associated with a tooth that can cause pain:

1. The tooth has nerves in the ligament around the OUTSIDE of the root that holds the tooth in the bone (illustrated below in orange).  Healthy nerves outside the tooth report pain when you bite into that unexpected piece of bone or hard seed.
2. The tooth also has nerves in the pulp, the tissue INSIDE of the tooth (illustrated below in blue). The nerves and blood supply to the pulp enter through tiny holes at the tips of the roots.  Healthy nerves in the tooth can give brief sensitivity when a tooth is bathed in a cold drink or ice cream.

If bacteria from a deep cavity encroach upon the pulp tissue or take over the pulp space of a tooth, the bacteria and inflammatory products spill out of the tiny holes at the root tip.  This irritates the nerves outside the root tips in the ligament we described earlier (1).  When these ligament nerves become irritated, biting into even soft things can cause discomfort; there can also be constant soreness or outright pain.  In simple terms, the goal of root canal treatment is to clean out the bacteria and inflamed or dying nerves in the pulp space, which in turn gradually eliminates inflammation of the ligament at the root tip.

Finally, the answer to the question we started off with: After a root canal, the nerve inside a tooth is indeed gone, but the nerves in the ligament outside the tooth remain very much alive.  There are a variety of ways the nerves of the ligament can be irritated and cause pain in a root canaled tooth.  Such conditions may include periodontal disease, an “unhealthy” bite, sinus problems, trauma, recent dental work and cracked teeth; additional root canal treatment in these cases is generally not appropriate. In a very small portion of root canaled teeth, bacteria hide in a natural crevice or crack that is inaccessible by the treating dentist/endodontist.  Furthermore, new decay or a leaking crown (particularly in teeth that had root canal treatment a long time ago) can allow bacteria to contaminate the root fillings and migrate to the root tips.  This bacteria can continue to irritate the ligament of the tooth and cause persisting discomfort; in those cases, root canal retreatment or root-end surgery may be useful (2).  Extraction, although a relatively aggressive procedure, would also be a treatment option.

If you are having persistent problems with a tooth that has undergone root canal treatment, call our office!  At Ellis Endodontics, our experienced endodontists will perform a thorough exam to determine the cause of discomfort.  We will also discuss with you what treatment options are appropriate for your specific situation.

1. Kakehashi S, Stanley HR, Fitzgerald RJ. The effects of surgical exposures of dental pulps in germ-free and conventional laboratory rats. Oral Surg Oral Med Oral Pathol 1965;20:340–9.
2. Tsesis I, Goldberger T, Taschieri S, Seifan M, Tamse A, Rosen E. The dynamics of periapical lesions in endodontically treated teeth that are left without intervention: a longitudinal study. J Endod 2013;12:1510-5.