Pulpitis and periapical periodontitis is a type of bacterial infectious disease, and bacteria frequently plant in the entire root canal system during the terminal stage. Main clinical treatment strategy of the disease requires root canal therapy, a key and core procedure for the successful treatment by thoroughly removing the root canal infection. The premise and guarantee of thoroughly removing root canal infection is by determining the accurate root canal working length. However, methods of accurately determining root canal working length, especially determining the position of apical stop, has been a hot topic among endodontic specialists, frequently causing confusion among many clinicians. This review provides a brief introduction of the complexity of the apical root anatomical structure, the confusion in determining the position of apical stop, and the method to determine the root canal working length.
