There are certain occasions when a root canal procedure seems to fail. Whenever something like this happens, the dentist at fault will usually try to redo the root canal so that it has been completed correctly. This dentist will probably go about the work of trying to remove the old filling materials that were used for the root (previously the endodontic cement that was used to seal it as well as the gutta percha). After that, he or she will attempt to reposition the tooth before replacing the materials that were taken out.
The problem, however, is that the old filling can be extremely hard to remove from the tooth. It makes it even harder if a post has already been placed into the hole in the tooth to help with the tooth preparation before a crown is placed. If this is the case, then an x-ray can be used to demonstrate the failure that is associated with the root. There is a surgical procedure that can be used to get rid of the offending root tip called an Apicoectomy. This procedure will also allow the dentist to get rid of any abscess that might have been associated with the failed root canal.
The procedure of an Apicoectomy is completed by cutting the soft tissue flap that is located just above the treated tooth where the tip of the root canal is showing. This cut will actually cut through the bone and amputate the tip of the root. The reason for this surgery is to try and get rid of the living or dead tissue that has been causing the problem. This usually will be enough to get rid of the problem but sometimes the dentist will make a small cavity preparation on the root's tip. After he or she does this the dentist will then seal off the canal with a small amalgam filling.
If it is not possible to do this small filling, then the dentist may also try a retrofill. A retrofill consists of melting some of the gutta percha at the root's tip to try and create a sealing. These two procedures (apicoectomies and retrofills) are usually a last ditch effort of a dentist in order to try and save the tooth that has been endodontically treated. They are more generally used in a failed root canal tooth that has a post inserted inside of the core. This is a way to create a sealing and salvage the tooth.