Root canal retreatment or periapical tissue operation should be done in order to reserve tooth after the root canal therapy failed. The key of the root canal retreatment is to remove the filling material in the root canal effectively. Now there are many instruments, however none of the retreatment methods produces completely clean root canal walls, and different instruments have discrepant efficiency. This review dedescribes the significance of the root canal retreatment, focusing on the research progress in the efficiency of removing the filling material in the root canal.
