The re-treatment of failed endodontic treatment includes complete removal of the root filling materials, shaping root canals, disinfection with medicaments and ultimately filling. The remnants within the root canal includes gutta-percha, debris and smear layer after thoroughly root canal preparation. Removing the old filling material is critical for success. The amount of the remnants indicate the ability of the re-treatment equipment. This review was to summarize the methods to evaluate the remnants.
