Fusion and gemination are developmental anomalies of teeth that may require endodontic treatment. Fusion may cause various clinical problems related to esthetics, tooth spacing, and other periodontal complications. Additional diagnostic tools are required for the diagnosis and the treatment planning of fused tooth. The present case report describes a case of unilateral fusion of a supernumerary root to an upper permanent central incisor with large periapical lesion in which a conservative approach was used without extraction of supernumerary tooth and obturated with mineral trioxide aggregate to reach a favorable outcome.

In dentistry, the term 'fusion' is used to describe a developmental disorder of dental hard tissues. In the permanent dentition, fusion of a normal tooth and a supernumerary tooth usually involves the incisors or canines. However, a few cases of fusion involving premolars have also been reported to date. We present a rare case in which fusion of the maxillary left second premolar and a supernumerary tooth in a 13-year-old girl was diagnosed using cone beam computed tomography (CBCT, Alphard-3030, Asahi Roentgen Ind. Co., Ltd.). The tooth was bicuspidized after routine nonsurgical root canal treatment, and the separated teeth underwent appropriate restoration procedures. The second premolar and supernumerary tooth remained asymptomatic without any signs of inflammation after a follow-up period of 9 years. Identification of anatomical anomalies is important for treatment in cases involving fusion with supernumerary tooth, and therefore the microscopic examinations and CBCT are essential for the diagnosis. Fused teeth can be effectively managed by the comprehensive treatment which includes both endodontic and periodontal procedures.