Altered Morphology of Teeth
A synonym for fusion is synodontia.
Fusion of teeth results from the union of adjacent tooth germs of developing teeth. Some authors think that fusion results when two tooth germs develop so close together that, as they grow, they contact and fuse before calcification. Other authors contend that a physical force or pressure produced during development causes contact of adjacent tooth buds. Males and females experience fusion in equal numbers; the incidence is higher in Asian and Native American and indigenous populations.
Fusion results in a reduced number of teeth in the arch. Although fusion is more common in the deciduous dentition, it may also occur in the permanent dentition. When a deciduous canine and lateral incisor fuse, the corresponding permanent lateral incisor may be absent. Fusion is more common in anterior teeth of both the permanent and the deciduous dentition. Fusion may be total or partial, depending on the stage of odontogenesis and the proximity of the developing teeth. The result can vary from a single tooth of about normal size to a tooth of nearly twice the normal size. The crowns of fused teeth usually appear to be large and single, although incisal clefts of varying depth or a bifid crown can sometimes occur.
Fusion of the central and lateral incisors in both the primary and the permanent dentitions. Note the reduction in number of teeth and the increased width of the fused tooth mass.
Images disclose the unusual shape or size of the fused teeth. The true nature and extent of the union are frequently more evident on the image than can be determined by clinical examination. Fused teeth may also show an unusual configuration of the pulp chamber or root canal.
The differential diagnosis for fused teeth includes gemination and macrodontia. Fusion may be differentiated from gemination when the number of teeth is reduced by one except in the unusual case in which a normal tooth and a supernumerary tooth have fused. The differentiation is usually academic because little difference exists in the treatment provided.
The management of a case of fusion depends on which teeth are involved, the degree of fusion, and the morphologic result. If the affected teeth are deciduous, they may be retained as they are. If the clinician contemplates extraction, it is important first to determine whether the permanent teeth are present. In the case of fused permanent teeth, the fused crowns may be reshaped with a restoration that mimics two independent crowns. The morphology of fused teeth requires radiologic examination before the teeth are reshaped. Endodontic therapy may be necessary and perhaps may be difficult or impossible if the root canals are of unusual shape. In some cases, it is most prudent to leave the teeth as they are.