Dental Education Lecture: Pain after Root Canal

We talk about root canal therapy in detail in last lecture.  It is a very complicated procedure.  We should do everything to prevent it from happening.  We should fix our bad habits (drinking coke, and eating candy) and have good habits (brushing diligently, flossing daily and visiting dental office regularly).  Periodic exam can find pretty early cavity as shown in black in Fig.1.  Simple filling (gray in Fig.2) is all we need to do.  It is difficult to get rid of our bad habits.  It is more difficult to get good habits.  Seeing a dentist is equal to finding trouble.  The end result is formation of more and deeper cavity as shown in Fig.3 and nerve infection (red).  In early nerve infection, you cannot identify which tooth causes trouble.  You have cold and hot sensitivity.  You cannot sleep tight in the evening.  Strangely enough, toothache is accompanied with real headache.  If you want to tough out, nerve infection sometimes spreads very fast within the nerve (pulp, green normal, red infected, Fig.4)  and outside the root tip (red circle).  By the time infection extends to outside, you know which tooth is a trouble maker.  You cannot chew with that tender tooth.  You have to get treatment.

 If you want to save the tooth, you need root canal therapy.  The doctor removes cavity and opens infected pulp (Fig.5), takes out coronal pulp (Fig.6), removes radical pulp (Fig.7), uses tiny files (blue, Fig.8) to file the canal (double arrows indicates up and down strokes of filing, rinses the canal with disinfectant solution (Fig.9) and finally fill the canal tightly with a rubber-like material (brown, Fig.10).  If we leave mildly infected nerve untreated for a long time, the canal become narrow (compare Fig.11 vs. Fig.8) and it is difficult to insert a file for mechanic cleansing.  

Occasionally the patient still experience discomfort after a pretty successful root canal therapy.  We are going to use Fig.12-15 to explain to you one of reasons so that you may help yourself out of this situation (pain after root canal).  Fig.12 shows a fairly common morphology of root canal system in root tip (normal).  Root canal may branch sideway in a very complicated manner.  For simplicity, we just show one of side branches (arrowhead).  Stiff metal file can be inserted into the main straight canal for taking out infected or uninfected (green) nerve, but it can not make a sharp turn to get into the sub-branch as indicated by arrowhead. After root canal therapy, the nerve in the sub-branch remains basically untouched (Fig.13).  Since this piece of the nerve is uninfected, it will not do us harm.  This happens only if we receive root canal therapy as soon as it is diagnosed.  If you want to tough out, the infection may spread to the main branched and sub-branched nerve, causing infection outside the root tip (two red circles, Fig.14).  After routine successful root canal therapy, we get rid of infection in the main branch and associated infection out the root tip (blank circle in Fig.15).  However, we do nothing about the infection in the sub-branch and that outside the root tip on the side.  That is why you still have pain after apparently successful root canal therapy.  If necessary, we need a surgery to remove the root tip above the infection area for cure.

Xin Wei, DDS, PhD, MS 1st edition 1/28/2009, last revision 03/05/2011