The Impact of Genetics and Environmental Factors on the Position of the Upper Third Molars.

ABSTRACT

PURPOSE: The purpose of this study was to estimate the importance of heredity in the position of the upper third molars. MATERIALS AND METHODS: Panoramic radiographs and lateral cephalograms of same-gender twins were analyzed. The determination of zygosity was performed by means of DNA tests with polymerase chain reaction for the amplification of short tandem repeats and 15 specific DNA markers. Data were estimated by the relative influence of additive genetic factors (A), nonadditive genetic factors (D), the common or shared environment (C), and unique environmental factors (E). RESULTS: The study sample consisted of 212 twins 80 dizygotic and 132 monozygotic twins. The genetic analysis showed that the best-fitting model for the size of the molars and their angulations was AE (additive genetic factors and unique environmental factors), in which the additive genetic factors had up to 84% influence and specific environment had up to 40%. Therefore, the ACE (additive genetic factors, common or shared environment, and unique environmental factors) model showed higher significance for the tooth eruption level. The heritability estimates were up to 59%, specific environment contributed up to 16%, and common environment reached 30%. CONCLUSIONS: Genetic factors play a key role in the position of the upper third molars.