The success of endodontic therapy depends on complete debridement and disinfection of the root canal system. Root canal therapy is based on accessing all areas in a root canal with mechanical and chemical means. Permanent mandibular incisors are generally perceived as teeth with a single root canal but the existence of a second canal has been pointed out. Inability to locate and disinfect the second canal in mandibular incisors leads to persistent periapical inflammation and failure of root canal treatment. Once this canal is located during the endodontic retreatment of these teeth, resolution of symptoms occurs. This case series will highlight the nonsurgical retreatment of permanent mandibular central and lateral incisors where the main cause of failure was a missed canal. In addition, a retrospective pilot study was carried out to find the endodontic failure of mandibular incisors owing to a missed canal. It was also observed that 73% of teeth had a single canal and 27% had a complex canal anatomy. A retrospective pilot study was carried out using seventy-five mandibular incisors that were indicated for root canal treatment and were evaluated using digital radiographs. It was also observed that 73% of teeth had a single canal and 27% had a complex canal anatomy. This case series will highlight the nonsurgical retreatment of permanent mandibular central and lateral incisors where the main cause of failure was a missed canal. It also throws light on different techniques to diagnose presence of a missed canal if any.