Supernumerary teeth are those that are in excess of the normal series. Supernumerary teeth can appear as a single tooth, multiple teeth, unilaterally or bilaterally, and in the maxilla, mandible, or both. The presence of this condition, particularly in the mandibular anterior region, has been reported infrequently. The purpose of this paper is to report and review the occurrence of such a rare combination. A 9-year-old girl presented to the Department of Pediatric and Preventive Dentistry with the chief complaint of a malpositioned tooth in the lower anterior region of the jaw. A supplemental tooth resembling a permanent central incisor was discovered during a clinical examination. The presence of Mesiodens was confirmed by radiographic examination. The mesiodens was extracted, followed by a spontaneous closure of the diastema. This case report revealed that the early detection of mandibular supplemental incisors could facilitate early intervention, a better prognosis, and fewer complications.