The use of cone-beam computed tomography (CBCT) can be decisive for diagnosis and treatment in certain cases. The presented clinical case illustrates the importance of CBCT imaging in identifying accessory canals of the lower incisors. A male patient showed on periapical radiography an extensive lesion involving the four lower incisor apices, on which partial endodontic treatment was performed. CBCT was performed and showed the presence of untreated accessory canals in the four teeth. After six months of endodontic retreatment and obturation of the accessory canals, new periapical radiography was performed. CBCT showed the presence of accessory canals in the four lower incisors, which was very important in the planning and subsequent endodontic retreatment.