Face

The face is probably the part of the body, which most distinguishes us as individuals. It plays a very important role in many functions, such as speech, mastication, and expression of emotion. In the face, there is a tight coupling between different complex structures, such as skin, fat, muscle, and bone. Biomechanically driven models of the face provide an opportunity to gain insight into how these different facial components interact. The benefits of this insight are manifold, including improved maxillofacial surgical planning, better understanding of speech mechanics, and more realistic facial animations. This chapter provides an overview of facial anatomy followed by a review of previous computational models of the face. These models include facial tissue constitutive relationships, facial muscle models, and finite element models. We also detail our efforts to develop novel general and subject-specific models. We present key results from simulations that highlight the realism of the face models

Simulation of Lipofilling Reconstructive Surgery using coupled Eulerian Fluid and Deformable Solid Models

International audienceWe present a method to simulate the outcome of reconstructive facial surgery based on fat-filling. Facial anatomy is complex: the fat is constrained between layers of tissues which behave as walls along the face; in addition, connective tissues that are present between these different layers also influence the fat-filling procedure. To simulate the end result, we propose a method which couples a 2.5D Eulerian fluid model for the fat and a finite element model for the soft tissues. The two models are coupled using the computation of the mechanical compliance matrix. Two contributions are presented in this paper: a solver for fluids which couples properties of solid tissues and fluid pressure, and an application of this solver to fat-filling surgery procedure simulation.Nous présentons une méthode pour simuler le résultat obtenu par la chirurgie reconstructive basée fat-filling. L'anatomie du visage est complexe: la graisse est contrainte entre les couches de tissues qui se comportent comme des murs le long du visage. De plus, des tissus connectifs sont présents entre ces différentes couches, donc influence la opération de fat-filling. Pour simuler le résultat final, nous proposons une méthode qui couple un fluide eulerien 2.5D pour la graisse et un modèle à éléments finis pour les tissus mous. Les deux modèles sont couplés en utilisant le calcul de la matrice de compliance. Deux contributions sont présentées dans ce papier: un solver pour les fluides qui couple les propriétés des tissus solides et la pression du fluide, puis une application de ce solver pour la simulation de le l'opération chirurgicale du fat-filling

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

Cranial sutures work collectively to distribute strain throughout the reptile skull

The skull is composed of many bones that come together at sutures. These sutures are important sites of growth, and as growth ceases some become fused while others remain patent. Their mechanical behaviour and how they interact with changing form and loadings to ensure balanced craniofacial development is still poorly understood. Early suture fusion often leads to disfiguring syndromes, thus is it imperative that we understand the function of sutures more clearly. By applying advanced engineering modelling techniques, we reveal for the first time that patent sutures generate a more widely distributed, high level of strain throughout the reptile skull. Without patent sutures, large regions of the skull are only subjected to infrequent low-level strains that could weaken the bone and result in abnormal development. Sutures are therefore not only sites of bone growth, but could also be essential for the modulation of strains necessary for normal growth and development in reptiles

The biomechanical role of the chondrocranium and sutures in a lizard cranium

The role of soft tissues in skull biomechanics remains poorly understood. Not least, the chondrocranium, the portion of the braincase which persists as cartilage with varying degrees of mineralization. It also remains commonplace to overlook the biomechanical role of sutures despite evidence that they alter strain distribution. Here, we examine the role of both the sutures and the chondrocranium in the South American tegu lizard Salvator merianae. We use multi-body dynamics analysis (MDA) to provide realistic loading conditions for anterior and posterior unilateral biting and a detailed finite element model to examine strain magnitude and distribution. We find that strains within the chondrocraniumare greatest during anterior biting and are primarily tensile; also that strain within the cranium is not greatly reduced by the presence of the chondrocraniumunless it is given the same material properties as bone. This result contradicts previous suggestions that the anterior portion (the nasal septum) acts as a supporting structure. Inclusion of sutures to the cranium model not only increases overall strain magnitudes but also leads to a more complex distribution of tension and compression rather than that of a beam under sagittal bending