Dental age and asymmetry in the formation of mandibular teeth in twins concordant or discordant for oral clefts.

The aims of this investigation were: 1) to study the effects of zygosity and the type of cleft on dental age in pairs of twins concordant or discordant for oral clefts, 2) to compare dental age in the twins with that in a population of normal Finnish children, and 3) to study asymmetry in the formation of mandibular teeth with regard to zygosity and the type of cleft. Twenty-two pairs of twins (8 mono- and 14 dizygotic) and one set of monozygotic triplets concordant or discordant for cleft lip (CL), cleft palate (CP), or both (CLP) were investigated. Four of eight mono- and 12 of 14 dizygotic pairs were discordant for clefts. An orthopantomogram of both twins was taken on the same day. In 7 of the 8 monozygotic (88%) and in 4 of the 14 dizygotic (29%) pairs, the dental age was the same in both twins. Of the 12 pairs discordant for clefts, the dental age of the twin with cleft was delayed in 5, advanced in 3, and the same in 4 compared with that of the twin without a cleft. The means of chronologic age and dental age were counted separately for the cleft subgroups and the non-cleft (NONC) group. The dental age was advanced in the CL twins and in the NONC twins, and was the same as chronologic age in the CP twins, but it was delayed in the CLP twins. Asymmetric formation of the 14 mandibular teeth (mostly the second premolars) was encountered in 3 of 8 CLP, in 3 of 18 CP, in 1 of 16 NONC, and in none of 5 CL children. The great similarity in tooth formation among the monozygotic twins indicates strong genetic control of dental maturation in twins concordant and also discordant for cleft.