While there is no predetermined limit for how many times a root canal can be retreated, with successive treatments, the results are unpredictable. Studies show that root canal treatment has an 86 to 98 percent success rate, which is very high. However, cleaning out the canals of a tooth can be tricky; if a dentist does not thoroughly remove infected tooth pulp, the infection will be sealed in the tooth, which can cause a number of problems later on. Retreatment has a 50 to 75 percent success rate and is always recommended to be performed by a highly skilled dentist, such as an endodontist.