Before the advent of microscopes, ultrasonic's, and micro management instruments retreatments were difficult, and performed sometimes at the sacrifice of remaining tooth structure which we now know makes a tooth prone to fracture.

Between the early 1980's and until the present apical surgery techniques have greatly improved. Retreatment techniques have also reached a level that it is rare that a tooth cannot be retreated unless the case presents as unrestorable or presents an obstacle that eliminates retreatment in the overall decision making process. Posts can be removed and most filling materials can be removed. Research insight tells us to retreat if at all possible before doing apical surgery. There are many reasons for this approach. Research and common sense tells us that unless the canal spaces are as clean as possible and obturated as tightly as possible the apical surgery procedure will likely fail. Apical retrofills are poor seals if the canal system is contaminated, and even worse seals if a canal has been missed such as MB2 in upper molars. Microbiology shows that the bacteria that makes the common carious lesion are different than the bacteria that occupy a canal space during a chronic necrotic pulp condition. With the exception of a few rotating bacterial strains the number of different strains of bacteria found in a root canal space to be around 11-15, and the same strains are usually found.

The interesting situation with a tooth that has already had RCT and has become reinfected is that the group of bacteria is different than those found in the first infection. So what? If a tooth has already had RCT and a crown, and if it shows healing on recall then gets another infection, say 11 years later, then the second group of bacteria do not need a new carious lesion to invade. They only need a point of leakage to set up another, different infection such as a crown that has come off repeatedly, an old access opening with a 10+ year old filling in it, a small crack, a broken cement seal, or redecay.

We see this evidence often when we re-access a previous endodontic treatment and find either black/tan stain or a foul odor or both. Another situation is when plastic core thermafils are encountered. These do not lend themselves to ultrasonic preps with small retroprep tips. It is preferable to remove these if possible especially if apical surgery is needed. Same holds for silver points. Many large lesions, though certainly not all, will heal following retreatment with calcium hydroxide. We encourage consultation visits for all previously treated teeth that are being evaluated for retreatment or apical surgery so that we discuss the treatment options, success rates, and any complexities of treatment.