The Evolution of Dental Morphology in Relation to Tooth Size, Crown Configuration, and Malocclusion
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Authors
Kenessey, Dorottya E.
Issue Date
2024
Type
Dissertation
Language
Keywords
Dental Crowding , Dental Morphology , Dental Variation , Malocclusion , Patterning Cascade Model , Tooth Size
Alternative Title
Abstract
Morphological traits comprise a large portion of the data analyzed in dental anthropological investigations. As a result, considerable work has been dedicated to illuminating the evolutionary and developmental mechanisms shaping phenotypic outcome. The overarching goal of the current project is to contribute to this discourse by exploring hypotheses related to developmental, evolutionary, and environmental factors influencing dental morphological trait expression. The first aim of this research is to revisit the relationship between crown area and dental morphological variation to determine the degree to which these phenotypes are related. The second aim of this work is to assess if expectations outlined by a prominent evolutionary developmental model are followed in the lower diphyodont human dentition. The third aim of this project is to establish dental crowding prevalence, a newly proposed nonmetric trait to be added to the suite of features examined in morphological analyses, in several global populations and discuss sociocultural and economic factors that may be impacting observed patterns. The first aim is evaluated in a large sample of modern humans (n=718) representing several biogeographical regions (k=3) and social identities (k=6). Dental metric data were collected directly from skeletal remains, while nonmetric data were assessed through visual observation. For the second aim, data on intercusp distances, crown area, and morphological trait expression were obtained from digital 3D scans of dental casts capturing diphyodont dental variation associated with a modern Solomon Island sample (n=124). The third aim provides information on dental crowding prevalence in several global populations (k=5) and social identity groups (k=7) utilizing a novel anthropological scoring procedure and demonstrates significant trait variation across samples. Malocclusion patterns are interpreted through a biocultural lens, discussing potential sociocultural ( i.e. , aesthetic preferences) and economic ( i.e ., access to care) factors mediating observed trait prevalence. The first study identified a significant relationship between crown size and morphological trait expression, whereby an increase in the former boosted the odds of more pronounced expression in the latter for accessory cusps characterized by size variation comparable to primary cusps ( i.e ., M 2 hypocone, M 1 Carabelli's trait, M 1 cusp 5, P 4 lingual cusp number, M 2 cusp 5, M 1 cusp 6). The significant relationship between crown size and morphology is proposed to reflect developmental modularity in these phenotypes. In the second study, cusp 6 was found to be the accessory cusp to most consistently follow expected model patterns in the deciduous and permanent dentitions. The development of a cusp 6 is hypothesized to cause more variability in cusp 5 expression, resulting in deviations from model predictions, while cusp 7 discrepancies are discussed in relation to inconsistent trait expression on the enamel and dentin surface. The third paper identified a high prevalence of minor crowding in Australia, while more severe forms were common in the Chinese and Japanese samples. Within social identity categories, South African Blacks and American Blacks displayed the lowest frequencies of crowding, while the South African Coloured and American Indigenous samples were characterized by the highest. These observed patterns are likely shaped by unique sociocultural and economic factors most pertinent to these groups. Overall, this project enhances understanding of the developmental, evolutionary, and environmental factors influencing dental morphological trait expression and variation. To continue improving knowledge of the different mechanisms implicated in dental phenotypic variation, collaboration between dental anthropologists and biobanks is recommended, opening up a variety of unexplored research avenues.
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Creative Commons Attribution 4.0 International