Mandibular canines usually have one root with one root canal. However, variations may occur. The present study reports two cases of successful retreatment of two mandibular canines with two roots and two root canals, a rarer configuration. In both cases reported, the unsuccessful treatment in the primary endodontic intervention was due to overlooking the lingual root canals, which were identified when periapical radiographs were taken at a mesial angle. Because canals missed during endodontic therapy may lead to periapical periodontitis, it is important to take radiographs from different angles, analyze the pulp chamber floor, and consider the variations in root canal morphologies. After performing the access cavity and observing an isthmus in both cases, the lingual root canals were located and instrumented. Calcium hydroxide dressing was used between appointments, and the root canals were filled with different sealers in each case (epoxy resin-based and bioceramic sealers). The follow-up X-rays taken 18 months later in the first case and 5 months later in the second case suggested normality of the periapical tissues. It is essential to use strategies that enable reaching the whole complexity of the root canal system during the canal cleaning, shaping, disinfection, and filling procedures in order to control the infection and achieve a successful endodontic treatment outcome.