Effect of Genetic and Environmental Factors on the Impaction of Lower Third Molars

The aim of this retrospective study was to evaluate the impact of genetic and environmental factors on the impaction of lower third molars using a classical twin study by evaluation of the third molar eruption space and M3 angulation. The study group consisted of 212 twins: 80 dizygotic and 132 monozygotic twins with digital panoramic radiograms and lateral cephalograms. The zygosity of twins was determined using 15 highly polymorphic DNA regions from the venous blood of twins. The results showed that differences between siblings in the dizygotic and monozygotic twin pairs were not statistically significant. The most fitting model for the angulations of lower third molars was AE (additive genetic and specific environmental effect), where the additive genetic factors had up to 88% influence and the specific environment up to 27%. Therefore, the ACE( additive genetic, common and specific environmental effect), model showed higher significance for the lower third molar eruption level where additive genetic estimates reached 71%, a specific environment contributed up to 15% and the common environment reached 32%. The conclusion was that a considerable proportion of the third molar impaction could be attributed to additive genetic effects and the common environment, whereas the specific environment had a lower, but significant impact.