A root canal can fail for several reasons. If the bacteria were not completely removed from the canals, they can grow and cause pain. Bacteria can also get inside a tooth if a permanent filling was not placed soon enough. Temporary fillings or poorly placed permanent fillings can break down or leak. This allows bacteria back into the canal.

Sometimes the problem is not in the root canal that was filled, but in another canal that the dentist did not find. The bacteria in this unfilled canal will grow and cause pain.

A repeat root canal treatment tends to be more involved and take more time than the first one. Your dentist must remove the crown, post and core, and filling material before doing the second root canal. Some people who need another treatment may have infections that are difficult to destroy. Because they take more time and can be complicated, second root canals also usually cost more.

Sometimes a second root canal can be hard to do. For example, it may be too risky to remove a post and core. The post that is in the tooth may be cemented or set in very tightly. If that is the case, the tooth may be injured in the process. So your dentist may decide to do endodontic surgery instead.

This surgery allows the dentist to get inside a tooth's root from the bottom of the tooth, rather than the top. Your dentist will not touch the crown of the tooth. The retreatment of the root canal will occur through the bottom of the root.

Endodontic surgery is done in the dentist's office. An endodontist, general dentist or oral surgeon can perform this procedure. First, you will receive a shot to numb the area. Then your dentist will make a small cut (incision) in the gum near the base of the tooth. He or she will clean out the infected tissue around the tip (apex) of the root and shave off the tip. This procedure is called an apicoectomy. The endodontist will clean the inside of the canal from the root end, and then put a filling in the end of the root. The incision is then stitched.

Endodontic surgery is successful about 85% of the time. If the surgery does not get rid of the infection, the tooth will have to be extracted.