Genetic and environmental contributions to variation in human tooth size.

Human dental crowns are complex structures without simple genetic or environmental determination, but mathematical modelling of data from family studies is now providing a more complete picture of their ontogeny. Mesiodistal (MD) and buccolingual (BL) dental crown diameters were recorded from almost 600 monozygotic and dizygotic twins, and univariate biometrical models were fitted to the data for 28 permanent teeth (excluding third molars). All 56 variables showed significant contributions of additive genetic variation, varying from 56 to 92% of phenotypic variation, with most being over 80%. The effects of individual or unique environment ranged from 8 to 29%. A significant effect of the environment shared by twins--either uterine or early childhood-- was found for MD and BL diameters of maxillary first molars (22-27%). There were also significant levels of non-additive genetic variation in MD diameters of canines and first premolars, which is consistent with selective pressures acting on these teeth at some stage in human evolution.