Abstract
The genetic traits commonly seen in teeth were studied by the twin method. The materials consisted of dental models and panoramic radiograms taken from 85 Chinese female pairs of twins at the mixed dentition stage. We examined the incidence rates of congenitally missing teeth except third molars, peg-shaped upper lateral incisors, shovel-shaped upper central incisors and Carabelli's tubercles on upper first molars, and the difference in concordance rates between the monozygotic and the dizydotic twins.
The results were as follows:
1. Congenitally missing teeth were found in 24 teeth of 19 twins, peg-shaped upper lateral incisors in 7 teeth of 7 twins, shovel-shaped upper central incisors in 122 teeth of 61 twins, Carabelli's tubercles in 66 teeth of 33 twins.
2. A significant difference in the concordance rates between the monozygotic and the dizydotic twins was observed only in the shovel-shaped upper central incisors.
3. After combining both the peg-shaped upper lateral incisors and the congenitally missing teeth into a same trait, a significant difference in the inter-pair concordance rate was also observed.
4. It is assumed that some genetic factors played significant roles both in the congenitally missing teeth including the peg-shaped upper lateral incisors and the shovel-shaped upper central incisors, any genetic effect for the Carabelli's tubercles on upper first molars was not, however, proved statistically.
