Bilateral twinning: report of case.

Twinning is an anomaly in which one tooth has combined with another or enlarged itself to the point of doubling its substance. A discussion of the nomenclature and a report of bilateral twinning are presented. A possible cause of the twinning events in this case include gemination of the maxillary right and mandibular left canines and fusion of the maxillary left and mandibular right canines with supernumerary teeth.