The procedure of doing a root canal is largely mechanical manipulation inside the tooth. The response to it is a biological response of healing. Even though the success rates for routine cases are very high, (93%), and success only decreases slightly in difficult cases if the objectives of treatment can be achieved, there is no guarantee for root canal procedures because of the biological response of healing. Even successful root canals may someday develop a problem. Two important factors are usually not considered to have a direct effect on the success of a root canal procedure, but ultimately help determine success and failure. One is the skill level of the dentist providing therapy, and the other is quality of the permanent restoration placed after the root canal is completed. Either of these two factors may result in the development, recurrence, or nonresolution of non-vital pathology associated with a tooth previously treated with root canal therapy. The decision to keep the tooth and avoid extraction must again be made. Once you have decided that you want to keep the tooth your dentist will advise you of the appropriate treatment decision for the tooth. The alternatives of root canal retreatment or endodontic root end surgery need to be considered.
Root canal retreatment should generally be the first consideration to save a tooth with a failed previous root canal. Retreatment may require removal of the existing post within the tooth, removal of the crown, and then the removal of the old root filling material(s), cleaning and shaping all the canals in all of the roots, identifying and correcting the problems encountered from the old root canal if possible. The canals are then refilled and sealed. There are circumstances that are not correctable by root canal retreatment and in which case endodontic surgery is indicated.
Endodontic surgery is indicated when there is a problem, such as an endodontic abscess, that cannot be corrected by a retreatment. The problem, usually seen on an x-ray, is that a blockage exists in the canal that prevents access, treatment, and correction of the root end area of the canal. Instead of treating the problem through the tooth, the problem can only be accessed and treated by treating the root tips directly. During surgery, a surgical operating microscope is utilized to identify the root end and the infection in the bone and a small amount of the root (about 3mm) is shaved off and the infection is scraped away. This is called an apicoectomy. Usually the root end is then prepared and a filling is placed. This root end filling is intended to seal the canal and prevent leakage of possible contamination out of it.
Surgery may also be a more appropriate treatment choice if the doctor and patient wish to avoid the time, trouble, and expense of removing and subsequently replacing the existing post and crown, or if the Specialist feels that clinical experience indicates a very low possibility of success through retreatment alone, thereby requiring the subsequent need for the additional surgical procedure as well, or if there is a need for replacement of the diseased bone through a regenerative procedure to help with the repair process by adding new bone and a protective healing membrane barrier.