Gingival abscess occurring in maxillary primary central incisor fused to supernumerary tooth

A 5Y7M-old girl was referred to our clinic by a general dentist for detailed examination of a recurrent gingival abscess in the maxillary left primary central incisor region. An intraoral examination revealed a diffuse swelling in the palatal gingiva area of the affected tooth. A periapical radiograph showed that the affected tooth was actually the primary central incisor and a supernumerary tooth, which had fused and been filled with composite resin at the juncture of the 2 tooth crowns. Removal of the filling induced severe bleeding and root canal treatment was performed. Radiographic examinations revealed 2 independent root canals, thus an additional access cavity to the mesial pulp cavity was produced for further root canal treatment. After the lesion had disappeared, root canal filling was performed using iodoform-calcium hydroxide paste and the affected tooth was restored with composite resin to fashion a single crown. However, the canal filling paste was later observed to be resorbed in the cervical area of the root. At 6Y0M, the patient received a traumatic injury in the anterior teeth region and the fused tooth was drastically displaced in a palatal direction, thus we extracted it under infiltration anesthesia. The root was observed to be wide in the mediodistal direction, and a histopathological examination revealed only dentin between 2 independent root canals. Our findings showed that the fused tooth was composed of 2 crowns and 1 root with 2 independent canals, and indicate that each crown and canal should have been treated separately.