The endpoint of an endodontic treatment must be situated at the cemen-to-dentinal junction to preserve the biological potential of the periapical area and to realize a complete disinfection of the principal root canal system. Thus, the determination of working length is a crucial factor in endodontic therapy. The conventional radiographic method cannot provide the accurate location of the apical constriction. For this reason, the electronic apex locators have been developed. Now, the last generation of apex locators has become more sophisticated and the electronic measurements seem to be accurate and reliable with electrolytic solutions in the canal.