Synonym:A synonym for gemination is twinning.
Gemination is a rare anomaly that arises when a single tooth bud attempts to divide. The result may be an invagination of the crown with partial division or, in rare cases, complete division through the crown and root, producing identical structures. Complete twinning results in a normal tooth plus a supernumerary tooth in the arch. The cause of gemination is unknown, but some evidence suggests that it is familial.
Although gemination may occur in both the deciduous and the permanent dentitions, it more frequently affects the primary teeth, usually in the incisor region. It can be detected clinically after the anomalous tooth erupts. The occurrence in males and females is about equal. The enamel or dentin of geminated teeth may be hypoplastic or hypocalcified.
Images reveal the altered shape of the hard tissue and pulp chamber of the geminated tooth. Radiopaque enamel outlines the clefts in the crowns and invaginations and accentuates them. The pulp chamber is usually single and enlarged and may be partially divided. In the rare case of premolar gemination, the tooth image suggests a molar with an enlarged crown and two roots.
Gemination of a mandibular lateral incisor showing bifurcation of the crown and pulp chamber. B, Almost complete gemination of a deciduous lateral incisor.
Gemination of a maxillary left second premolar on cross-sectional slices. B, Three-dimensional surface rendering demonstrating the geminating tooth and its association with the premolar. C, Coronal CBCT image of another case of gemination of a second premolar. Note the common root canal. (A and B, Courtesy Dr. B. Friedland, Cambridge, MA.)
The differential diagnosis of gemination includes fusion. If the malformed tooth is counted as one, individuals with gemination have a normal tooth count, whereas individuals with fusion are seen to be missing a tooth.
A geminated tooth in the anterior region may compromise arch esthetics and arch length. Areas of hypoplasia and invagination lines or areas of coronal separation represent caries-susceptible sites that may in time result in pulpal inflammation. Affected teeth can cause malocclusion and lead to periodontal disease. Consequently, the affected tooth may be removed (especially if it is deciduous), the crown may be restored or reshaped, or the tooth may be left untreated and periodically examined to preclude the development of complications. Before treatment is initiated on a primary tooth, the status of the permanent tooth and configuration of its root canals should be determined by imaging.