An isthmus is defined as a narrow, ribbon- shaped communication between two root canals that contains pulp tissues. It can act as a bacterial reservoir which is difficult to prepare, shape and fill, and thus accounts for the failure of root canal therapy. The location and treatment of the canal isthmus may be a prerequisite to successful surgical endodontics. Now, with the adjunct of dental operating microscope and endoscope in routine endodontic procedures, clinicians can view the resected root surface better, identify and prepare the isthmus. The recognition and management of the canal isthmus may be advantageous in increasing the success rate of surgical endodontics.
