Endodontic therapy has a well documented rate of success. There are situations where initial endodontic therapy fails. In a
previous post, we discussed the role of bacteria in root canal failure despite the separation of a rotary instrument.
Root canal failure, as well as failure of any dental treatment, is often associated with bacteria. Bacteria that is incompletely removed from the canal system during endodontic treatment will cause root canal failure. Unfortunately, sometimes that failure is not identified until months or years later and then some people condemn root canal therapy as unsuccessful, when the cause may be
incomplete root canal therapy leaving bacteria behind in the canals.
The following example is a root canal that was done 13 months ago by an associate dentist in a general dental practice. This can sometimes create a difficult situation for the owner dentist, when the patient returns with an abscess a year later.
 |
| Root canal done 13 months earlier. Large periapical lesion on mesial root. Short root canal filling on mesial canals. The prognosis for this tooth was poor at the time of completion because the MB canal was not cleaned and obturated. Bacterial left behind will continue to cause periapical disease. |
 |
| CBCT shows missed MB canal and short ML canal filling. |
 |
| Missed MB canal located immediately with microscope. |
 |
| All canals cleaned and shaped. This tooth now has good prognosis for success. |
As mentioned, bacteria left behind will cause failure of root canal treatment. Root canal failure is most often caused by failure to completely remove bacteria from the canal system or failure to seal out bacteria from re-entering the canal system.
