title: The relationship between skull morphology, masticatory muscle force and cranial skeletal deformation during biting.
abstract: The human skull is gracile when compared to many Middle Pleistocene hominins. It has been argued that it is less able to generate and withstand high masticatory forces, and that the morphology of the lower portion of the modern human face correlates most strongly with dietary characteristics. This study uses geometric morphometrics and finite element analysis (FEA) to assess the relationship between skull morphology, muscle force and cranial deformations arising from biting, which is relevant in understanding how skull morphology relates to mastication. The three-dimensional skull anatomies of 20 individuals were reconstructed from medical computed tomograms. Maximal contractile muscle forces were estimated from muscular anatomical cross-sectional areas (CSAs). Fifty-nine landmarks were used to represent skull morphology. A partial least squares analysis was performed to assess the association between skull shape and muscle force, and FEA was used to compare the deformation (strains) generated during incisor and molar bites in two individuals representing extremes of morphological variation in the sample. The results showed that only the proportion of total muscle CSA accounted for by the temporalis appears associated with skull morphology, albeit weekly. However, individuals with a large temporalis tend to possess a relatively wider face, a narrower, more vertically oriented maxilla and a lower positioning of the coronoid process. The FEAs showed that, despite differences in morphology, biting results in similar modes of deformation for both crania, but with localised lower magnitudes of strains arising in the individual with the narrowest, most vertically oriented maxilla. Our results suggest that the morphology of the maxilla modulates the transmission of forces generated during mastication to the rest of the cranium by deforming less in individuals with the ability to generate proportionately larger temporalis muscle forces.
authors.affiliation: Department of Archaeology and Hull York Medical School, University of York, Heslington, York YO10 5DD, United Kingdom; Facultad de Odontología, Universidad de Chile, Sergio Livingstone Pohlhammer 943, Independencia, Región Metropolitana, Chile; Max Planck Institute for Evolutionary Anthropology, Department of Human Evolution, Deutscher Platz 6, 04103 Leipzig, Germany. Electronic address: mtoroibacache@odontologia.uchile.cl.
authors.forename: Viviana
authors.initials: V
authors.lastname: Toro-Ibacache
authors.affiliation: Centro de Imagenología, Hospital Clínico Universidad de Chile, Santos Dumont 999, Independencia, Región Metropolitana, Chile.
authors.forename: Víctor
authors.initials: V
authors.lastname: Zapata Muñoz
authors.affiliation: Department of Archaeology and Hull York Medical School, University of York, Heslington, York YO10 5DD, United Kingdom.
authors.forename: Paul
authors.initials: P
authors.lastname: O'Higgins
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019412:Anatomy, Cross-Sectional; D001696:Biomechanical Phenomena; D001732:Bite Force; D005145:Face / Q000033:anatomy & histology; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007180:Incisor / Q000033:anatomy & histology / Q000502:physiology; D008297:Male; D008409:Mastication / Q000502:physiology*; D008410:Masticatory Muscles / Q000033:anatomy & histology* / Q000502:physiology*; D008437:Maxilla / Q000033:anatomy & histology; D008875:Middle Aged; D008963:Molar / Q000033:anatomy & histology / Q000502:physiology; D012727:Sex Characteristics; D012886:Skull / Q000033:anatomy & histology*
keywords: Finite element analysis; Geometric morphometrics; Masticatory function; Modern humans; Skull morphology