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Why do humans have chins? Testing the mechanical significance of modern human symphyseal morphology with finite element analysis

Gröning, Flora; Liu, Jia; Fagan, Michael J.; O'Higgins, Paul

Authors

Flora Gröning

Jia Liu

Paul O'Higgins



Abstract

The modern human mandibular symphysis differs from those of all other primates in being vertically orientated and possessing a chin, but the functional significance of this unique morphology is not well understood. Some hypotheses propose that it is an adaptation to specific loads occurring during masticatory function. This study uses finite element analysis to examine these symphyseal loads in a model of a modern human mandible. By modifying the symphyseal cross-sectional form, the mechanical significance of the presence of the chin and symphyseal orientation is tested, and modern human and Neanderthal symphyseal cross-sections are compared with regard to their ability to withstand different loads. The results show that changes in symphyseal form have profound effects on the strains. The presence of a chin leads to lower symphyseal strains overall, whereas a vertical orientation of the symphysis results in higher strains under wishboning, but not under vertical bending in the coronal plane and dorsoventral shear. Compared to Neanderthals, the modern human symphysis shows higher strains during dorsoventral shear and wishboning, but is as effective as the Neanderthal symphysis in resisting vertical bending in the coronal plane and the loads resulting from simulated incision and unilateral molar biting. In general, the results of this study corroborate prior hypotheses about the mechanical effects of the human chin and vertical symphyseal orientation and support the idea that the relative importance of wishboning and vertical bending in the coronal plane might have played a role in the evolution of modern human symphyseal morphology.

Journal Article Type Article
Publication Date 2011-04
Journal AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY
Print ISSN 0002-9483
Electronic ISSN 1096-8644
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 144
Issue 4
Pages 593-606
APA6 Citation Gröning, F., Liu, J., Fagan, M. J., & O'Higgins, P. (2011). Why do humans have chins? Testing the mechanical significance of modern human symphyseal morphology with finite element analysis. American journal of physical anthropology, 144(4), 593-606. https://doi.org/10.1002/ajpa.21447
DOI https://doi.org/10.1002/ajpa.21447
Keywords chin mandible biomechanics Neanderthals finite element analysis human temporomandibular-joint mandibular symphysis cortical bone elastic properties pleistocene homo stress-analysis biomechanics evolution muscle tissue
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