Taurodontism in twins with cleft lip and/or palate.

The aims of this study were to determine the frequency of taurodontism of the first and second permanent molars in twins discordant or concordant for clefts, the frequency for each type of cleft in twins, and the concordance-discordance ratio in mono- and dizygotic twins. Thirty-nine pairs of twins (13 monozygotic, 26 dizygotic) between the ages of 7 and 23 yrs were investigated. Taurodontism and hypodontia were determined from orthopantomograms of the dentition. Of the 39 pairs of twins investigated, 16 (41%) had taurodontism, equally in mono- and dizygotic pairs. The highest frequency of the trait was noted in subjects with isolated cleft palate and the lowest in cleft lip subjects. Four of 13 monozygotic pairs with taurodontism were concordant for the trait, as were 9 of 12 dizygotic pairs. Taurodontism was symmetric in 91% of the affected molar pairs. Concomitant taurodontism and hypodontia was observed in 8 of 16 taurodontic twin pairs. We conclude that the etiology of clefting in our group of twins seems to have an effect on the frequency of taurodontism. A high concordance for taurodontism and a high symmetry of the trait may indicate a strong genetic etiology of taurodontism.