Yannick Tillier

Determination of Young's modulus of mandibular bone using inverse analysis.

Development of a numerical model applicable to clinical practice, and in particular oral implantology, requires knowledge of the mechanical properties of mandibular bone. The wide range of mechanical parameters found in the literature prompted us to develop an inverse analysis method that takes into account the exact geometry of each specimen tested, regardless of its shape. The Youngs modulus of 3000MPa we determined for mandibular bone using this approach is lower than the values reported in the literature. This difference can be explained by numerous experimental factors, related in particular to the bone specimens used. However, the main reason is that, unlike most previously published papers on the subject, the heterogeneity of bone led us to select a specimen size at the upper end of the scale, close to clinical reality.

Stress distribution in the temporo-mandibular joint discs during jaw closing: a high-resolution three-dimensional finite-element model analysis.

PurposeThis study aims at analysing the stresses distribution in the temporomandibular joint (TMJ) using a complete high-resolution finite element model (FE Model). This model is used here to analyse the stresses distribution in the discs during a closing jaw cycle. In the end, this model enables the prediction of the stress evolution in the TMJ disc submitted to various loadings induced by mandibular trauma, surgery or parafunction.Materials and methodsThe geometric data for the model were obtained from MRI and CT scans images of a healthy male patient. Surface and volume meshes were successively obtained using a 3D image segmentation software (AMIRA®). Bone components of skull and mandible, both of joint discs, temporomandibular capsules and ligaments and dental arches were meshed as separate bodies. The volume meshes were transferred to the FE analysis software (FORGE®). Material properties were assigned for each region. Boundary conditions for closing jaw simulations were represented by different load directions of jaws muscles. The von Mises stresses distribution in both joint discs during closing conditions was analyzed.ResultsThe pattern of von Mises stresses in the TMJ discs is non-symmetric and changed continuously during jaw movement. Maximal stress is reached on the surface disc in areas in contact with others bodies.ConclusionsThe three-dimension finite element model of masticatory system will make it possible to simulate different conditions that appear to be important in the cascade of events leading to joint damage.

Three-dimensional finite element modelling for soft tissues surgery

Abstract Laparoscopy is a surgical technique that requires fine control from the surgeon point of view. Up to this day, this experience can only be obtained by intensive training. That is why a lot of training simulators have been developed in the medical area. We present here a new approach based on a three-dimensional finite element software and an elastic constitutive equation, able to predict realistic results. This software has been applied to soft tissues deformation, namely lamb kidney and human uterus, and the numerical results are compared to experimental ones.

Finite element modeling for soft tissue surgery based on linear and nonlinear elasticity behavior

New surgical techniques require fine control from the surgeons point of view. Until recently, the necessary experience was only obtainable through traditional training protocols (using cadavers, animals, etc.). However, numerous training simulators have now been developed for use in this area. We present a new approach based on a three-dimensional finite element software and on different kinds of linear and nonlinear elastic constitutive equations that is able to predict realistic results. To classify these equations in terms of accuracy, we performed ex-vivo experimental measurements on lamb kidneys. The software has been applied to soft tissue deformation, namely lamb kidney and human uterus, and the numerical results have been compared to experimental ones.

Comparison of stress distribution in the temporomandibular joint during jaw closing before and after symphyseal distraction: a finite element study

The aim of this study was to predict stress modification in the temporomandibular joint (TMJ) after symphyseal distraction (SD). The study was performed using three-dimensional finite element analysis using a complete mastication model. Geometric data were obtained from MRI and CT scans of a healthy male patient and each component was meshed as various regions. The distraction was performed with a 10mm expansion after simulation of a surgical vertical osteotomy line on the model in the mandibular midline region. The geometry and mesh of the bone callus were constructed. The bone callus was modelled as a strengthened region characterized by a Youngs modulus corresponding to consolidated bone to predict the long-term biomechanical effect of SD. Boundary conditions for jaw closing simulations were represented by different jaw muscle load directions. The von Mises stress distributions in both joint discs and condyles during closing conditions were analysed and compared before and after SD. Stress distribution was similar in discs and on condylar surfaces in the pre- and post-distraction models. The outcomes of this study suggest that anatomical changes in TMJ structures should not predispose to long-term tissue fatigue and demonstrate the absence of clinical permanent TMJ symptoms after SD.

Mise au pointApport de la méthode des éléments finis en chirurgie maxillofacialeContribution of the finite element method in maxillofacial surgery

The finite element method is a numerical modeling tool used in various fields in medicine and surgery such as orthopedics, traumatology, and cardiovascular surgery. But this tool also has several applications in maxillofacial surgery. We present the advantages of this method by describing its principles as well as the various fields of application in maxillofacial surgery. This article was intended to help novices understand the results of various studies using this method.

Apport de la méthode des éléments finis en chirurgie maxillofaciale

The finite element method is a numerical modeling tool used in various fields in medicine and surgery such as orthopedics, traumatology, and cardiovascular surgery. But this tool also has several applications in maxillofacial surgery. We present the advantages of this method by describing its principles as well as the various fields of application in maxillofacial surgery. This article was intended to help novices understand the results of various studies using this method.

Diffusion–reaction model to describe osteogenesis within a titanium scaffold

Bone is a living tissue able to rebuild and restore its physical and geometrical properties when it is injured. However, when a defect exceeds a critical size, bone tissues cannot regenerate themselves. Therefore, a structural support such as a scaffold is required to fill the defect in order to enable the loads transmission but also to promote osteogenesis (Karageorgiou and Kaplan 2005). Osteogenesis is triggered by migration and proliferation of mesenchymal stem cells (MSCs), which depending on the biochemical and mechanical environments may later differentiate into fibroblasts, chondrocytes or osteoblasts. Then, these last three types of cells create their own extracellular matrix (i.e. fibrous tissue, cartilage tissue and bone tissue, respectively). During the last decade, several computational models have been developed to simulate the bone ingrowth within a scaffold subjected to an external static load (Byrne et al. 2007; Checa and Prendergast 2010; Sandino et al. 2010). These models are mostly based on mechano-regulation theories (Carter et al. 1988; Prendergast et al. 1997), which relate the mechanical stimuli to the differentiation pathways of the bone cells previously cited. Here, we develop a two-dimensional (2D) multiscale and multiphysics finite element model to simulate bone ingrowth within a titanium scaffold subjected to a cyclic load. The main goal of this study is to evaluate the effects of the mechanical stresses on the cellular activity, i.e. the mechanotransduction phenomenon. In particular, we show how the diffusion and the proliferation of the cells are affected by the mechanical environment.

Electrofusion Welding Process Optimization Using a Coupled Numerical and Experimental Approach

Abstract In the water and gas distribution industry, electrofusion is one of the main techniques used for welding polyethylene pipes. In order to help understanding the origin of some defects discovered recently and to optimize and predict the welding quality, we developed a coupled numerical and experimental approach. Our numerical model, that computes a weld quality index based on molecular interdiffusion, is able to reasonably well predict whether welding will occur or not depending on the welding conditions imposed.

Mechanical characterization of aortic valve tissues using an inverse analysis approach.

The use of numerical simulation to investigate heart and valvular mechanics is becoming increasingly popular. In particular, finite element analysis is often used to support the operation planning procedure as well as the design of new prostheses with mechanical properties as close as possible to those of natural tissues and an even better biocompatibility. With one of the highest prevalence of cardiovascular degenerative diseases [1], aortic valves (AV) have been widely studied during the last decades. The elastic [2] and time-dependent [3] behaviors of the AV leaflets under physiological biaxial loading states have been previously investigated in the literature over a wide range of loading conditions.. As most soft tissues, AV has an oriented network of collagen fibers embedded in an elastin matrix, which is responsible for their hyperelastic and anisotropic behaviors. Accordingly, non-linear transverse isotropic constitutive equations are often used assuming a macroscopically-identifiable preferred fiber direction. In this study a new method is proposed in order to estimate relevant material and structural properties of AV while reducing at the same time the number of complex and time-consuming experiments. An inverse analysis procedure based on the finite element computation of planar biaxial tensile tests was used to set-up a reduced protocol. This protocol was then experimentally reproduced to identify real material parameters. The obtained material parameters will be later used to model heart valve tissues.