Tooth fusion consists of the union of crowns by the enamel and/or dentin. We describe a case of a patient who presented with a fistula in the apical portion of teeth 32 and 33. Clinically, tooth 32 showed increased crown width in relation to other teeth in the same arch. Radiographic examination evidenced fusion of tooth 32 with a possible supernumerary tooth. Cone-beam computed tomography was used to confirm the radiographic findings and revealed incomplete apex formation of the supernumerary tooth. The fused tooth was subjected to root canal treatment. Calcium hydroxide was used as intracanal medication, changed for every 30 days, for 4 months. Subsequently, the mesial canal received an apical plug of mineral trioxide aggregate mixed with distilled water. At 2 years of follow-up, the tooth showed signs of tissue repair.