What do the indigenous people of the Amazon have to teach us about the etiology of dental malocclusion?

Abstract

Studies in both human and nonhuman primates have historically linked the rising prevalence of malocclusion to changes in dietary consistency and food processing. However, the evaluation of semi-isolated indigenous populations with preserved traditional habits offers a unique opportunity to investigate the true origins of occlusal and craniofacial variation. Over more than a decade, we have evaluated five Amazon indigenous groups from the Middle Valley of the Xingu River, characterized by exclusive breastfeeding, absence of pacifier use, uniform patterns of occlusal tooth wear, and well-documented genetic profiles indicating low intratribal and high intertribal variation. The prevalence of malocclusion ranged from 33.8 % to 66.7 %, overall lower than that observed in urban Amazon populations, around 85 %. The lower prevalence of posterior crossbite may be related to prolonged breastfeeding and an absence of pacifiers in the indigenous groups. Despite cultural and environmental homogeneity, a high degree of intertribal diversity was found in occlusal features, facial morphology, dental arch dimensions, and dental crowding, while a small intragroup variation was observed. In a 13-year follow-up, dental crowding and tooth wear increased, while the arch dimensions tended to decrease, suggesting that the effect of increased tooth wear on the etiology of tertiary crowding is of small magnitude and restricted to the lower dental arch. These findings suggest that genetic factors play a central role in determining the dentofacial characteristics, challenging the theory that diet consistency could be the principal cause of modern malocclusion. The evidence from these indigenous populations supports the view that occlusal and craniofacial morphology are primarily influenced by polygenic inheritance, with environmental factors contributing selectively to specific dentoalveolar traits.