A functional analysis of Carabelli trait in Australian Aboriginal dentition

Carabelli is a non-metric dental trait that can be found on both second deciduous molars and first permanent molars, ranging from a small pit to a prominent cusp. The degree of expression and frequency of this accessory trait in modern humans can vary individually and across populations, which suggests a strong genetic basis [1]. Due to its capacity to vary at many levels of expression, Carabelli trait has been frequently employed in anthropological and archaeological studies for reconstructing phylogenetic relationships, population affinities and for the determination of individual identity, such as ethnicity, gender and age. However, whilst emphasis is placed on the formation and expression frequencies of Carabelli trait, little evidence exists on its functional attributions to mastication. In this study, we examine molar macrowear with the aim of reconstructing Carabelli trait occlusal dynamics occurring during mastication using Occlusal Fingerprint Analysis (OFA), a quantitative digital approach that can be used to reconstruct the jaw movements of an individual by examining the molar macrowear patterns [2]. Here, we explore the functional implication of Carabelli trait in the dentition of children and young adults from Yuendumu, an Australian Aboriginal population that was at an early stage of transition from a nomadic and hunter-gatherer way of life to a more settled existence [3]. We analysed permanent and deciduous molars of upper and lower arches with a slight to moderate degree of wear, based on dental stone casts showing the presence of Carabelli trait in occlusion (N = 96), with age groups ranging from 7.05 to 34.53 years of age. We also considered the degree of expression of Carabelli trait by using the Arizona State University Dental Anthropology System (ASUDAS), a standardized system consisting of a series of rank-scale plaques used to assess dental morphological (or nonmetric) variation in human populations [4]. Our results demonstrate that Carabelli trait slightly enlarges the surface functional area, especially in those molars where this feature is expressed in its cuspal form and it is closer to the occlusal plane. Moreover, the highly steep contact planes would also indicate that Carabelli wear areas contribute in increasing shearing abilities, which are particularly important when chewing fibrous and tough foods [5]. Overall, the macrowear analysis suggests that Carabelli trait in the Aboriginal people from Yuendumu slightly enhanced occlusion and likely played some functional role during mastication. Future biomechanical and microwear analyses could provide additional information on the mechanical adaptation of Carabelli trait in modern human dentition.