Dental morphology is highly differentiated among human populations and research indicates that it may be influenced by genetic factors.
Teeth vary among individuals in size and shape. In addition, there are certain dental characteristics that are more common in certain populations. For example, in Asian and derived populations, synodontia is common and includes a combination of dental characteristics with first and second incisors that are spade-shaped and not aligned with the rest of the teeth, upper first premolars with a single root and lower first molars with three roots. In particular, shovel-shaped incisors show clear regional differences, being very frequent in Asia and Native Americans and rare or absent in Africa and Europe.
Spade-shaped incisors are characterized by lingual surfaces with marked marginal ridges, with significant curvature at the crown. It is a trait that has been investigated for a long time, especially by anthropologists who have used it to study relationships between populations. It seems clear that it is a genetic trait, with an estimated heritability of 75% and associated with genes involved in the developmental pathways of organs and tissues of ectodermal origin, although the polymorphisms influencing this trait are not fully established.
The morphology of the teeth, especially whether they are spade-shaped or not, which is the most studied characteristic, is a highly heritable trait that is highly conditioned by geographic ancestry. Thus, it is more common to find shovel-shaped teeth among the inherited physiognomy of Asian and Indo-American populations than among individuals of African or European ancestry.
Several studies have identified a marker associated with the likelihood of shovel-shaped upper incisors. This marker is found in the EDAR gene, which produces the ectodysplasin A protein receptor. This gene has also been associated on other occasions with the development of other traits such as hair or nails. In fact, dysfunctional mutations in EDAR are known to be responsible for hypohidrotic ectodermal dysplasia in humans, a genetic disorder that causes abnormal morphogenesis of teeth, hair and sweat glands.
13.5 million variants
Kimura R, Yamaguchi T, Takeda M, Kondo O, Toma T, Haneji K, et al. A Common Variation in EDAR Is a Genetic Determinant of Shovel-Shaped Incisors. Am. J. Hum. Genet. 2009 Oct;85(4):528–35.
Park JH, Yamaguchi T, Watanabe C, Kawaguchi A, Haneji K, Takeda M, Kim YI, Tomoyasu Y, Watanabe M, Oota H, Hanihara T, Ishida H, Maki K, Park SB, Kimura R. Effects of an Asian-specific nonsynonymous EDAR variant on multiple dental traits. J Hum Genet. 2012 Aug;57(8):508-14.