Bone orthotropic remodeling as a thermodynamically-driven evolution

International audienceIn this contribution we present and discuss a model of bone remodeling set up in the framework of the theory of generalized continuum mechanics and first introduced by DiCarlo et al.[1]. Bone is described as an orthotropic body experiencing remodeling as a rotation of its microstruc-ture. Thus, the complete kinematic description of a material point is provided by its position in space and a rotation tensor describing the orientation of its microstructure. Material motion is driven by energetic considerations , namely by the application of the Clausius-Duhem inequality to the microstructured material. Within this framework of orthotropic re-modeling, some key features of the remodeling equilibrium configurations are deduced in the case of homogeneous strain or stress loading conditions. First, it is shown that remodeling equilibrium configurations correspond to energy extrema. Second, stability of the remodeling equilibrium configurations is assessed in terms of the local convexity of the strain and complementary energy functionals hence recovering some classical energy theorems. Eventually, it is shown that the remodeling equilibrium configurations are not only highly dependent on the loading conditions, but also on the material properties

Ultrasonic characterization and multiscale analysis for the evaluation of dental implant stability: a sensitivity study Biomedical Signal Processing and Control 42 (2018) 37-44

International audienceWith the aim of surgical success, the evaluation of dental implant long-term stability is an important task for dentists. About that, the complexity of the newly formed bone and the complex boundary conditions at the bone-implant interface induce the main difficulties. In this context, for the quantitative evaluation of primary and secondary stabilities of dental implants, ultrasound based techniques have already been proven to be effective. The microstructure, the mechanical properties and the geometry of the bone-implant system affect the ultrasonic response. The aim of this work is to extract relevant information about primary stability from the complex ultrasonic signal obtained from a probe screwed to the implant. To do this, signal processing based on multiscale analysis has been used. The comparison between experimental and numerical results has been carried out, and a correlation has been observed between the multifractal signature and the stability. Furthermore, a sensitivity study has shown that the variation of certain parameters (i.e. central frequency and trabecular bone density) does not lead to a change in the response

Caractérisation de la Réponse Ultrasonore d'Implant Dentaire : Simulation Numérique et Analyse des Signaux

International audienceThe long-term success of a dental implant is related to the properties of the bone-implant interface. It is important to follow the evolution of bone remodeling phenomena around the implant. To date, there is no satisfactory method for tracking physiological and mechanical properties of this area, and it is difficult for clinicians to qualitatively and quantitatively assess the stability of a dental implant. In this context, methods based on ultrasound wave propagation were already successfully used by our group, in the qualitative and quantitative evaluation of primary and secondary stability of dental implants. In this study we perform numerical simulations, using the finite element method, of wave propagation in a dental implant inserted into bone. To simplify the calculations, an axisymmetric geometry is considered. Given the importance of monitoring of peri-prosthetic area, particular attention is given to the boundary conditions between the implant and the bone. The numerical results are compared with those from experimental tests. These results, numerical and experimental, are then analysed with signal processing tools based on multifractal methods. Analysis of the first results shows that these methods are potentially efficient in this case because they can explore and exploit the multi-scale structure of the signal

Multimodal assesment of the biomechanical properties of the bone-implant interface

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Numerical simulation of the influence of the poroelastic nature of human trabecular bone on ultrasonic wave propagation

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Novel techniques in breast cancer screening.

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Experimental identification of a prior tensor-valued random field for the elasticity properties of cortical bones using in vivo ultrasonic measurements

International audienceA cortical bone layer is a biomechanical system which is difficult to model due to the complexity level of its microstructure. The experimental identification of its effective mechanical properties at the macroscale is usually carried out using the axial transmission technique which is often modeled with a mean mechanical model. In this paper, the mean mechanical model is made up of a fluid-solid semi- infinite multilayer system (skin and muscles/cortical layer/marrow). It is also assumed that the effective elasticity properties of the solid layer (cortical bone) have spatial variations in the thickness (osteoporosis). The uncertainties introduced in the mean mechanical model are taken into account in introducing a prior stochastic model in which the elasticity tensor is modeled by a non- homogeneous non-Gaussian tensor-valued random field. The parameters of the random field are a spatial correlation length, a space dependent dispersion parameter and the values of the elasticity tensor of the simplified mean mechanical model. A method and an application are presented for the identification of these parameters using in vivo experimental measurements in ultrasonic range with the axial transmission technique

Finite difference time domain numerical simulation of ultrasonic propagation in coated contrast agents

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