A finite element study of the human cranium : the impact of morphological variation on biting performance

This thesis investigated the relationship between craniofacial morphology and masticatory mechanics using finite element analysis (FEA). Chapter 1 is a literature review of the relevant background: bone mechanics, jaw-elevator muscle anatomy, imaging techniques, FEA and geometric morphometrics.The second, third and fourth chapters comprise experimental work aiming to provide a framework for FE model construction and loading. The second chapter aimed to validate the method for FE model building and assess the sensitivity of models to simplifications. Models with simplified bone anatomy and resolution predicted strains close to those measured experimentally. The third chapter assessed the predictability of muscle cross-sectional area (CSA) from bony features. It was found that muscle CSA, an estimator of muscle force, has low predictability. The fourth chapter assessed FE model sensitivity to variations in applied muscle forces. Results showed that a cranial FE model behaved reasonably robustly under variations in the muscle loading regimen.Chapter 5 uses the conclusions from the previous studies to build FE models of six human crania, including two individuals with artificial deformations of the neurocranium. Despite differences in form and the presence of deformation, all performed similarly during biting, varying mainly in the magnitudes of performance parameters. The main differences related to the form of the maxilla, irrespective of neurocranial deformation. The most orthognatic individuals with the narrowest maxilla showed the most distinctive deformation during incisor and molar bites, and achieved the greatest bite force efficiency. However, bite forces were similar among individuals irrespective of the presence of artificial deformation. This appears to relate to the preservation of normal dental occlusion, which in turn maintains similar loading and so morphogenesis of the mid face. Altogether, the results of this thesis show that FEA is reliable in comparing masticatory system functioning and point to how variations in morphology impact skeletal performance

Differences in masticatory loads impact facial bone surface remodeling in an archaeological sample of South American individuals

The reduction of masticatory strains is considered one of the main factors that led to a pronounced morphological variation of the facial skeleton among modern humans. Although the archaeological record has provided evidence of bone remodeling activity being linked to craniofacial variation, its link with subsistence strategies has been proposed but not yet tested. Here, we evaluate the relationship between the strains arising from masticatory loads in the facial bones and the observed surface bone remodeling activity in adults and subadults from archaeological sites from South America that exerted different masticatory loads during life. We simulated the impact of mechanical loading during I1 and M1 bite using finite element analysis in six skulls from two archaeological samples, one of hunter-gatherers from Patagonia and the other of horticulturists from Northwest Argentina. The extension and distribution of bone formation and resorption were registered by a periosteal bone surface analysis on facial bones. We found a similar spatial distribution of high and low strains between samples and across ages, but different magnitudes. In general, compression strains corresponded with resorption activity, while tension strains corresponded with formation activity. Our results show a relationship between mechanical bone response to masticatory loading and bone remodeling activity, which can ultimately shape cranial morphology. We propose that although there are differences in skull morphology among populations that are established early in ontogeny, mechanical loading produced during mastication can enhance such differences. These results then support the idea that craniofacial morphology can contribute to reconstructing the history of past populations.Fil: Brachetta Aporta, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina. Universidad de Chile; Chile. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento de Antropología; ArgentinaFil: Toro Ibacache, María Viviana. Universidad de Chile; Chile. Institut Max Planck for Evolutionary Anthropology; Alemani

Jaw kinematics in South African Plio-Pleistocene hominins inferred from maxillary molar root morphology: implications for species identification

Max Planck Society FONDECYT (Chile) 11150175 FR-TAF3890 CGL2010-2086

Geometric morphometrics and the study of biologic shapes: From descriptive to quantitative morphology Morfometría geométrica y el estudio de las formas biológicas: De la morfología descriptiva a la morfología cuantitativa

Morphometrics is the study of co-variation of biological form and its causes. Its development over the last decades has reached several biological sciences with a traditional descriptive approach, such as morphological sciences. The new geometric morphometric tools allow not only objective quantitative analysis, but also to assess qualitative traits due to the chance of recovering the form under study. This is possible because of the application of biometry techniques, instruments and software that allow the acquisition and analysis of shape coordinates that represent the geometry of the specimen, and that are not limited to obtaining linear data that lack of precision and amount of information of geometric data. Geometric morphometric analysis consists of three fundamental steps: obtaining primary data, obtaining shape variables and statistical analysis. The extensive use of this technique in areas related to morphological sciences over the last years makes geometric morphometrics a

Vitamin D and adolescent idiopathic scoliosis, should we stop the hype? A cross-sectional observational prospective study based on a geometric morphometrics approach

[Purpose]: There is strong evidence supporting the presence of fluctuating asymmetry (FA) in Adolescents with Idiopathic Scoliosis (AIS). Additionally, recent research investigating the relationship between vitamin D and AIS found a relation between them. We hypothesize a negative correlation between FA and vitamin D.[Methods]: We performed a surface scan of the torso of 53 AIS patients, a blood test to measure vitamin D and the radiographic Cobb angle. A correlation analysis between vitamin D and FA was carried out to test our hypothesis, and a regression of vitamin D on 3D shape was performed to observe shape differences between the vitamin D deficiency and insufficiency groups.[Results]: There was no correlation between vitamin D and FA. We found a strong negative correlation between vitamin D and the Cobb angle only in the premenarche group (n = 7; r = - 0.92). Differences in shape were observed between the deficiency and insufficiency groups, and that differences were related to the width of the torso, but not the rotation or lateral flexion.[Conclusions]: Our results do not support the massive screening of vitamin D in AIS. Shape analysis revealed differences between the shape of the deficiency and insufficiency groups related to robustness. However, this finding had no relation with the scoliosis characteristics, it just reflected different body composition, and its importance should be explored in future.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Research was funded by grant number PID2020-115854GB-I00 to Markus Bastir, José María González Ruiz, and Carlos A. Palancar, by MCIN/AEI/10.13039/501100011033 of the Spanish Ministry of Science and Innovation and the European Union.Peer reviewe