Análisis biomecánico en la zona para-radicular de primer molar con y sin la aplicación de micro-osteoperforaciones en mandíbula. Estudio en Elementos Finitos / Para-root zone biomechanical analysis with and without the application of micro-osteoperforations in the jaw: Finite Elements Study

RESUMEN Objetivo: El propósito del presente estudio fue investigar biomecánicamente si el tratamiento con micro-osteoperforaciones (Mops) genera diferencias de desplazamiento y de tensiones a nivel óseo cuando se aplica una carga ortodóncica, mediante el uso de análisis de elementos finitos. Material y Método: Un modelo de mandíbula dentada donde se eliminó el segundo premolar fue utilizado para el análisis. Posteriormente, se dividieron en 3 muestras dependiendo de la posición de las Mops: 1) Sin Mops (control); 2) Mops 1 mm adyacentes al primer molar; 3) Mops a 4 mm del molar. Para la simulación, se aplicó una carga estática horizontal de 150 gr (1,5N), simulando un resorte cerrado de Nitinol, tanto a nivel molar en dirección mesial como a nivel interproximal entre canino e incisivo lateral en dirección distal. Resultados: A pesar que se observó una ligera tendencia a aumentar el desplazamiento del molar con la presencia de Mops, no existieron mayores variaciones en relación a las magnitudes de desplazamiento ni tensiones entre los diferentes modelos. Conclusiones: Desde el punto de vista biomecánico no existen diferencias evidentes en los valores de tensiones ni de desplazamiento entre los modelos analizados.

ABSTRACT: Objective: The purpose of the present study was to biomechanically investigate if the treatment with micro-osteoperforations (Mops) generates displacement and tensions differences at bone level when an orthodontic load is applied, through the use of finite element analysis. Material and Method: A toothed jaw model where the second premolar was removed was used for the analysis. Subsequently, they were divided into 3 samples depending on the position of the Mops: 1) Without Mops (control); 2) Mops adjacent 1 mm to the first molar; 3) Mops 4 mm to molar. To simulate a closed Nitinol spring, an horizontal static load of 150 gr (1.5N) was applied, both at molar level in the mesial direction and at interproximal level between the canine and the lateral incisor in the distal direction. Results: Although a slight tendency to increase the displacement of the molar with the presence of Mops was observed, there were no major variations in relation to the magnitudes of displacement or tensions between the different models. Conclusions: From the biomechanical point of view, there are no obvious differences in the values of stresses or displacement between the models analyzed.

Simulation method of skull remodellingsurgeryfor infant with craniosynostosis / 生物医学工程学杂志

Craniofacial malformation caused by premature fusion of cranial suture of infants has a serious impact on their growth. The purpose of skull remodeling surgery for infants with craniosynostosis is to expand the skull and allow the brain to grow properly. There are no standardized treatments for skull remodeling surgery at the present, and the postoperative effect can be hardly assessed reasonably. Children with sagittal craniosynostosis were selected as the research objects. By analyzing the morphological characteristics of the patients, the point cloud registration of the skull distortion region with the ideal skull model was performed, and a plan of skull cutting and remodeling surgery was generated. A finite element model of the infant skull was used to predict the growth trend after remodeling surgery. Finally, an experimental study of surgery simulation was carried out with a child with a typical sagittal craniosynostosis. The evaluation results showed that the repositioning and stitching of bone plates effectively improved the morphology of the abnormal parts of the skull and had a normal growth trend. The child's preoperative cephalic index was 65.31%, and became 71.50% after 9 months' growth simulation. The simulation of the skull remodeling provides a reference for surgical plan design. The skull remodeling approach significantly improves postoperative effect, and it could be extended to the generation of cutting and remodeling plans and postoperative evaluations for treatment on other types of craniosynostosis.

Análisis Biomecánico de una Prótesis de Cadera mediante Elementos Finitos / Biomechanical Analysis of a Hip Prosthesis Using a Finite Element

Resumen En el presente trabajo se plantea un análisis biomecánico de una prótesis de cadera bajo condiciones de cargas estáticas asociadas a actividades cotidianas, en el cual se comparan tres materiales metálicos para la fabricación de una prótesis personalizada a partir de imágenes médicas. Se utilizaron plataformas en la nube de diseño asistido por computadora y de análisis por elementos finitos. Se diseñaron dos modelos de la prótesis a analizar, uno hueco y otro sólido mediante curvas spline paramétricas. Para el análisis biomecánico se requirió un tamaño de malla de 2,537,684 de elementos tetraédricos y 471,335 nodos para estudiar siete casos de posturas para una persona de 75 kg de peso, mismos que se analizaron tomando como materiales base acero inoxidable 316L, aleación Ti-6AL-4V y L-605. Se observó que con actividades tales como trotar, subir y bajar escaleras los materiales 316L y L-605, presentan el riesgo de deformación plástica e inclusive fractura. Los resultados mostraron que el material más idóneo para la fabricación de este tipo de prótesis es el Ti-6Al-4V, además de que este nos permite realizar modelos tanto sólidos como huecos, suponiendo este último, un ahorro de material y proporcionando mayor ligereza en la prótesis.

Abstract This paper shows a biomechanical analysis of a hip prosthesis under conditions of static loads associated with daily activities. For which it compared three metallic materials for the manufacture of a customized prosthesis from medical images, it was used cloud platforms with computer-aided design and finite element analysis. Two models of prosthesis one hollow and the other one solid using parametric spline curves were designed and analyzed. The biomechanical analysis required a mesh size consisting of 2,537,684 tetrahedral elements and 471,335 nodes to study seven cases of postures for a person weighing 75 kg. These cases were analyzed based on 316L stainless steel, Ti-6AL-4V alloy, and another L-605 alloy. It was observed that with activities such as jogging, climbing and descending stairs, materials 316L, and L-605 present the risk of plastic deformation and even fracture. The results show that the most suitable material for the manufacture of this type of prosthesis is the Ti-6Al-4V, which allows us to make both solid and hollow models. Assuming this last material is saved and improves the prosthesis lightness.

Tomografía computarizada y sólidos virtuales para obtener modelos biomecánicos computacionales / Computed tomography and virtual solids to obtain computational biomechanical models

Uno de los padecimientos más comunes de los huesos es la fractura, definida como la pérdida de la continuidad del material óseo. Implantes y prótesis son utilizados para tratar algunas de ellas. Actualmente, antes de usar uno de estos dispositivos, se prueban modelos virtuales de los mismos utilizando un programa de diseño asistido por computadora. Para dichas pruebas, se requieren también modelos virtuales de los huesos. Los modelos óseos son obtenidos aplicando técnicas de segmentación de imágenes a las tomografías computarizadas (TC). Este trabajo presenta un procedimiento para la obtención de modelos biomecánicos hueso-implante a partir de las TCs y sólidos virtuales, teniendo en cuenta la estructura real de los huesos, compuesta de tejido cortical y trabecular. Para realizar los análisis de verificación del procedimiento se utilizó un modelo de un implante DHS y de una prótesis de cadera(AU)

One of the most common bone conditions is fracture, defined as the loss of the continuity of the bone material. Implants and prostheses are used to treat some of them. Currently, before using one of these devices, virtual models are tested using a computer-aided design program. For these tests, virtual models of the bones are also required. Bone models are obtained by applying image segmentation techniques to computed tomography (CT). This paper presents a procedure for obtaining biomechanical bone-implant models from the CTs and virtual solids, taking into account the real structure of the bones, composed of cortical and trabecular tissue. A DHS implant model and a hip prosthesis were used to perform the procedure verification tests(AU)

Use of Models of Finite Elements in the Biomechanics of the Lumbar Spine

The same correspondence between general mechanics and civil engineering is true for biomechanics and surgical implants. Currently, numerous mechanical processes are required until a prosthesis is offered to its target audience. These processes typically require human or animal vertebrae, as well as all the complexity involving such tissues, for example, an ethics committee, the availabilityofmaterials, etc. Thus,finite elementmodels (FEMs) havebecome a great option to carry out biomechanical tests independently from anatomical specimens, and, at the same time, to obtain mathematical data to assist in the general physical understanding. The present review discusses the mechanical principles involved in bioengineering, clarifies the steps for the development of FEMs, and shows application scenarios for thesemodels. To the knowledge of the authors, the present paper is the first review study in Portuguese aimed to health care professionals in a language accessible to them.

Evaluation of shear bond strength and shear stress on zirconia reinforced lithium silicate and high translucency zirconia

This study evaluated the shear stress distribution on the adhesive interface and the bond strength between resin cement and two ceramics. For finite element analysis (FEA), a tridimensional model was made using computer-aided design software. This model consisted of a ceramic slice (10x10x2mm) partially embedded on acrylic resin with a resin cement cylinder (Ø=3.4 mm and h=3mm) cemented on the external surface. Results of maximum principal stress and maximum principal shear were obtained to evaluate the stress generated on the ceramic and the cylinder surfaces. In order to reproduce the in vitro test, similar samples to the computational model were manufactured according to ceramic material (Zirconia reinforced lithium silicate - ZLS and high translucency Zirconia - YZHT), (N=48, n=12). Half of the specimens were submitted to shear bond test after 24h using a universal testing machine (0.5 mm/min, 50kgf) until fracture. The other half was stored (a) (180 days, water, 37ºC) prior to the test. Bond strength was calculated in MPa and submitted to analysis of variance. The results showed that ceramic material influenced bond strength mean values (p=0.002), while aging did not: YZHT (19.80±6.44)a, YZHTa (17.95±7.21)a, ZLS (11.88±5.40)b, ZLSa (11.76±3.32)b. FEA results showed tensile and shear stress on ceramic and cylinder surfaces with more intensity on their periphery. Although the stress distribution was similar for both conditions, YZHT showed higher bond strength values; however, both materials seemed to promote durable bond strength.

Modelling side to side intestinal anastomosis

Side-to-side intestinal anastomosis is a surgical procedure where an incision is performed between two parallel segments of gut and then they are sutured together. The purpose of this paper is to investigate if the standard surgical practice diameter used in anastomosis leads to undesirable closed circulatory flows which may be harmful to the gut tissue. A finite element model for the chyme flow in a side by side anastomosis with realistic user configurable parameters is developed and solved in a wide range of situations. We analyze the flow crossing the anastomosis, the normalized pressure difference in the gut section and the streamlines that show the presence or absence of closed flow regions for a set of surgically feasible anastomosis diameter values. In contrast with the findings of simpler analytical models, closed flows do not appear in any of these cases. The study shows that the current standard surgical practice where the anastomosis diameter is similar to the gut diameter does not lead to undesirable effects predicted by some simple analytical models.

Control of the maxillary occlusal plane by micro-implant in the process of en-mass retraction:A finite element analysis / 实用口腔医学杂志

Objective:To investigate the changes of occlusal plane in the process of retracting maxillary anterior teeth with different vertical traction force.Methods:The three dimensional finite element model of maxillary anterior teeth en-masse retraction by micro-implant was constructed with cone beam CT scanning and MIMICS and ANSYS software.Then the movement tendency of tooth and the changes of the maxillary occlusal plane was calculated when the vertical traction force was 0,0.5,0.75 and 1 N in the process of en-mass retraction,respectively.Results:Lingual tipping of anterior teeth,distal tipping of the first molar and the maxillary occlusal plane clockwise rotation by the retraction forces were observed.With the vertical traction force increasing,lingual tipping of anterior teeth and distal tipping of the first molar were decreased,and the occlusal plane clockwise rotation was prevented.Conclusion:The upper dentition movement and occlusal plane rotation can be changed effectively by the vertical traction with different force.When retract anterior teeth,0.5-0.75 N vertical traction force is beneficial to prevent clockwise rotation of the maxillary occlusal plane.

Influence of the occlusal contacts in formation of Abfraction Lesions in the upper premolar / Influência dos contatos oclusais na formação de lesões de Abfração no pré-molar superior

Objective: The aim of this study was to observe the influence of different occlusal contacts in a superior pre-molar structure using Finite Element Analysis. Material and Methods: A three-dimensional model of a superior pre-molar was designed to simulate three occlusion situations, namely central occlusion and two types of lateral occlusion contacts. The model presents enamel, dentin, a periodontal ligament and a fixation cylinder separately. All materials were considered isotropic, linear and homogeneous, and the contacts of each structure were perfectly bonded. On analysis software, a load was applied to an occlusal surface at 40° to the long axis on lateral contacts, and directed to the long axis on central occlusion contact. Results: The results were obtained in stress maps and the maximum values were then plotted in table for quantitative comparison, with the enamel concentrating more stress than dentin and the occlusal contact presenting the worst biomechanical behavior. Conclusion: Within the limitations of this study, it is possible conclude that: eccentric contacts have higher potential to develop abfraction lesions on the cervical region of teeth, thus increasing the magnitude of tensile and shear stresses. (AU)

Objetivo: observar a influência de diferentes contatos oclusais em uma estrutura pré-molar superior usando a análise por elementos finitos. Material e Métodos: um modelo tridimensional de pré-molar superior foi projetado para simular três situações de oclusão: oclusão central e dois tipos de contatos de oclusão lateral. O modelo apresentou esmalte, dentina, ligamento periodontal e um cilindro de fixação separadamente. Todos os materiais foram considerados isotrópicos, lineares e homogêneos, e os contatos de cada estrutura foram considerados perfeitamente ligados. No software de análise, aplicou-se uma carga na superfície oclusal a 40°, ao longo eixo do dente, nos contatos laterais e direcionada para apical no contato de oclusão central. Resultados: os resultados foram obtidos nos mapas de tensão e os valores máximos foram escritos em tabela para comparação quantitativa, com o esmalte concentrando mais tensão do que a dentina e o contato em cúspide de balanceio apresentando o pior comportamento biomecânico. Conclusão: dentro das limitações deste estudo, é possível concluir que: os contatos excêntricos facilitam o surgimento de lesões de abfração na região cervical dos dentes, pois aumentam a magnitude das tensões de tração e de cisalhamento. (AU)

Biomechanical behavior of indirect composite materials: a 3D-FEA study / Comportamento biomecânico de resinas compostas indiretas: um estudo 3D-FEA

Objective: Este estudo teve como objetivo avaliar a influência do módulo de elasticidade de resinas compostas indiretas (RCI) na distribuição de tensão de um primeiro pré-molar superior restaurado. Materiais e métodos: Um modelo de elemento finito tridimensional (3D) de um dente com restauração mesio-ocluso-distal (MOD) foi utilizado. Foram simulados três RCI, alterando o módulo de elasticidade: 10, 15 e 20 GPa. Todos os materiais foram considerados isotrópicos, homogêneos, lineares e elásticos. Uma carga axial (200 N) foi aplicada na superfície oclusal através de uma esfera, e os nós da superfície externa das raízes foram fixados. Foi analisada a Tensão Máxima Principal no dente e na restauração. Resultados: De acordo com a análise, quanto menor for o módulo elástico da RCI, maiores são os valores de tensão de tração gerados no dente. Para a restauração, observou-se o oposto: quanto menor o módulo, menor a tensão de tração. Conclusão: Com as limitações deste estudo, é possível concluir que quanto maior o módulo de elasticidade do material restaurador, mais difícil será a deflexão das cúspides, mas, a fratura da resina será mais fácil.(AU)

Objetivo: This study aimed to evaluate the influence of the elastic modulus of indirect composite resins (ICR) in the stress distribution of a restored maxillary first premolar. Material and methods: A three-dimensional (3D) finite element model of the tooth and the mesialocclusal-distal (MOD) restoration was created. Three ICR were simulated, by changing the elastic modulus: 10, 15 and 20 GPa. All materials were considered as isotropic, homogeneous and linearly elastic. An occlusal load (200 N) was applied on occlusal surface trough a sphere, and the nodes of the external surface of the root were fixed. The maximum principal stresses on the tooth and restoration were analyzed. Results: According to FE analysis, the lower the ICR elastic modulus, the higher the tensile stress values generated on the remaining tooth. For the restoration, the opposite was observed: the lower the modulus, the lower the tensile stress. Conclusion: With the limitations of this study it is possible to conclude that the greater the elastic modulus of the restorative material the harder it will be to deflect the cusps, but the easier the fracture of the resin(AU)

Stress and strain distributions on short implants with two different prosthetic connections ­ an in vitro and in silico analysis / Distribuições de tensão e microdeformação em implantes curtos com duas conexões protéticas diferentes - uma análise in vitro e in silico

Objetivo: Uma biomecânica ideal que minimiza a tensão entre implante e osso pode proporcionar sucesso para implantes osseointegrados. Este estudo avaliou a concentração de deformação no tecido circundante e a tensão nos componentes de dois implantes com diferentes conexões protéticas através de métodos in vitro e in silico. Material e Métodos: Vinte blocos de poliuretano foram divididos em dois grupos (n = 10), seguido da instalação de hexágono interno (IH) (AS Tecnologia - Titanium Fix, São José dos Campos, Brasil) ou de implantes cone morse (LT) (Bicon Dental Implants). Para o método da extensometria (SG), foram colocados quatro sensores ao redor dos implantes. Para a análise por elementos finitos (FEA), o mesmo bloco foi modelado e analisado. Foi aplicada uma carga axial (30 kgf) para ambas as metodologias. Os valores de tensão e deformação foram analisados quanto à correlação com o SG. Resultados: Para SG, LT apresentou uma média de deformação mais agressiva (-932) que IH (-632). Para FEA, a LT mostrou menor tensão (-547) que IH (-1169). Conclusão: Para os dois sistemas implantes, os valores de microdeformação capazes de induzir remodelação óssea indesejada não foram medidos. No entanto, para o implante IH, a presença de um parafuso de retenção tem a desvantagem de concentrar a tensão, enquanto um pilar sólido dissipa a carga axial através do implante, o que sugere um melhor desempenho para o grupo LT. (AU)

Objective: An ideal biomechanics minimizes the stress between implant and bone that can provide success for osseointegrated implants. This study evaluated the strain concentration in surrounding tissue and stress in the components of two implants with different prosthetic connections through an in vitro and in silico methods. Methods: Twenty polyurethane blocks were divided into two groups (n=10) followed by the installation of internal hexagon (IH) (AS Technology ­ Titanium Fix, São José dos Campos, Brazil) or locking taper implants (LT) (Bicon Dental Implants). For strain gauge (SG) method, four sensors were placed around the implants. For finite element analysis (FEA), the same block was modeled and analyzed. An axial load (30 kgf) was applied for both methodologies. The values of stress and strain were analyzed for correlation to SG. Results: For SG, LT presented a mean of strain most aggressive (-932) than IH (-632). For FEA, LT showed less stress (-547) then IH (-1169). Conclusion: For two implant's system, microstrain values capable to induce unwanted bone remodeling were not measured. However, for IH implant, the presence of a retention screw has the disadvantage to concentrate stress while a solid abutment dissipates the axial load through the implant that suggests a better performance for LT group(AU)

Propuesta de modelo de trauma vascular mediante la caracterización mecánica de prótesis endovasculares (stents) a través del análisis estructural con técnicas FEA / Proposed model of vascular trauma by mean of mechanical characterization of endovascular prostheses (stents) based on structural analysis by FEA

Resumen Objetivo Tras las evidencias acumuladas mediante el uso de técnicas de angioplastia con stents, surge la polémica sobre los factores que inciden en la respuesta final, ya que hay estudios que reportan reestenosis de la luz en el 30-40% alrededor de 6 meses luego de ser implantados, vinculándose como una de las causas al diseño del dispositivo. Este artículo propone la caracterización funcional de stents endovasculares, analizando su influencia mecánica en el sistema vascular y prediciendo los factores de trauma implícitos en el lecho de los vasos. Métodos Utilizando modelos computacionales de prótesis endovasculares tipo stents, mediante técnicas Finite Elements Analysis, se procedió al análisis estructural de dichos dispositivos con el fin de predecir el comportamiento mecánico y el trauma vascular. Para ello, las prótesis fueron consideradas estructuras tubulares compuestas por múltiples eslabones que están sometidos a cargas de presión, que se reflejan como concentradores de esfuerzos. Resultados El estudio permitió visualizar cómo se ajusta la geometría del stent a las diferentes cargas, obteniéndose una aproximación a la respuesta de interacción "sólido-sólido" entre el stent y la pared arterial. Así, se caracterizó el patrón de esfuerzos y se planteó un modelo conceptual que explica su incidencia mecánica en la interacción stent-vaso, para inferir en la funcionalidad del diseño del dispositivo. Conclusiones El modelo conceptual planteado permite determinar la relación entre las condiciones de interacción mecánicas del stent, y advierte sobre los efectos en lo que sería la operación del dispositivo en el ambiente vascular.

Abstract Objective The accumulated evidence on angioplasty techniques with stents has raised a controversy about the factors that influence the final vascular response. Indeed, several studies have shown there might be re-stenosis between 30% to 40% about 6 months after placement, relating to the design of the device as one of the main causes. This paper proposes the functional characterization of endovascular stents, analyzing its mechanical influence in the vascular system and predicting implicit traumatic factors in the vessel. Methods A structural analysis was made for several computational models of endovascular stents using Finite Element Analysis in order to predict the mechanical behavior and the vascular trauma. In this way, the stents were considered as tubular devices composed of multiple links under radial pressure loads, reflecting stress concentration effects. Results The analysis allowed to visualize how the geometry of stents is adjusted under several load conditions, in order to obtain the response of "solid-solid" interaction between the stent and the arterial wall. Thus, an analysis was performed in order to calculate stress, and a conceptual model that explains its mechanical impact on the stent-vessel interaction, was raised, to infer on the functionality from the design of the devices. Conclusions The proposed conceptual model allows to determine the relationship between the conditions of mechanical interaction of the stents, and warns about the effects in what would be the operation of the device on the vascular environment.

Estudio comparativo sobre el comportamiento y la distribución de las tensiones en implantes dentales cortos e implantes dentales estándares en la región posterior del maxilar superior: Un estudio en elementos finitos / Comparative study on the behaviour and tension distribution in short and standard dental implants in the back of the upper jaw

Objetivos Estudios concluyen que la máxima tensión y distribución de fuerzas se produciría alrededor del cuello del implante. Comparar la distribución de las tensiones entre un implante dental corto oseointegrado en distintas disponibilidades óseas verticales y un implante estándar oseointegrado en el sector posterior del maxilar en un terreno mixto formado por hueso propio del paciente y Bio-Oss®. Conocer la distribución de las tensiones. Estudiar el aumento del diámetro del implante corto. Analizar si los resultados avalan el uso de implantes cortos. Material y método El método de elementos finitos (MEF), que permite resolver ecuaciones diferenciales asociadas a un problema físico sobre geometrías complicadas. En este trabajo la región geométrica es un modelo tridimensional de un implante, su corona, y una porción de la región ósea de la zona estudiada. Los modelos fueron sometidos a fuerzas de oclusión de 150 N en ángulo de 30° Norma ISO 14801:2003. El software de MEF que se utiliza es el ABAQUS de la empresa Dassault Systèmes. Resultados Máximos valores se concentran en la porción cervical del implante. Las tensiones en el implante están dentro del mismo rango. A mayor módulo de elasticidad de los elementos que componen los modelos, mayor es la absorción de las fuerzas. Las tensiones en el hueso cortical no mostraron diferencias, pero en el modelo que aumentamos el diámetro del implante a 4,8 se produce una marcada disminución de las tensiones. La comparativa de las tensiones en el hueso esponjoso muestra que existe diferencia en las tensiones producidas en el hueso con Bio-Oss® y está localizado en la porción apical del implante quedando lejos de la zona de mayor concentración de los esfuerzos. Conclusiones La máxima concentración de las fuerzas a nivel cervical es independiente de la longitud del implante, siendo más favorable el aumento del diámetro. El uso de implantes cortos en hueso de baja calidad parece posible.

Objectives Current studies conclude that the maximum tension and the greater distribution of forces should occur around the implant neck. To compare the distribution of stress between a short dental implant osseointegrated in different available vertical bones and standard osseointegrated implants in the posterior maxilla in mixed terrain formed by the bone of the patient and Bio-Oss®. To determine the stress distribution. To study the increased diameter of the short implant. To determine whether the results support the use of short implants. Materials and methods The finite elements method (FEM), which helps to solve differential equations associated with a physical problem with complicated geometries, was used in this work, where the geometric region is a three-dimensional model of an implant, its crown, and a portion of the bone region of the studied area. The models were subjected to occlusion forces, 150 N Angle 30° ISO 14801: 2003. The MEF software used was called Abaqus from Dasssault Systemes Enterprise. Results The maximum values were concentrated in the cervical portion of the implant. Tensions in the implant are in the same range. The greater the elasticity of the elements contained in the module, the greater is the absorption of stress forces. The tension in the cortical bone showed no differences, but in the model where the diameter of the implant is increased to 4.8, a marked decrease occurs in the bone stress. The comparison of the stresses in the cancellous bone showed a difference in the stresses produced in the bone with Bio-Oss®, and it is located in the apical portion of the implant away from the area of the major stress concentration. Conclusions The maximum concentration of forces in cervical portion is independent of the length of the implant, being favourable to increase the diameter. It is possible to use low quality bone in for shorts implants.

Consideraciones en la definición del modelo específico al paciente de la tibia / Considerations about the definition of a patient specific model of the tibia

INTRODUCCIÓN: los análisis por elementos finitos se usan para entender y predecir los procesos biológicos. En la biomecánica ortopédica, los modelos específicos al paciente se generan a partir de Tomografía Computarizada y empleados en la toma de decisiones médicas. Algunos procesos correctivos ortopédicos pueden simularse a través, de los análisis por elementos finitos. Para obtener modelos biomecánicos confiables, es muy recomendable reducir los errores en la definición del modelo en la etapa de pre-procesamiento del análisis por elementos finitos. OBJETIVO: analizar la influencia de la densidad del mallado y las propiedades mecánicas durante la definición del modelo específico al paciente en los resultados del análisis por elementos finitos. MÉTODOS: se empleó el Método de Elementos Finitos en la simulación de la tibia a compresión. La geometría de la tibia del paciente se generó a partir de Tomografía Computarizada. Se emplearon mallas con tamaño de elementos no uniforme y uniforme. Al modelo se le aplicaron propiedades mecánicas homogéneas y no homogéneas. RESULTADOS: los elementos de bajo orden convergen a la solución, las tensiones para las mallas con estos elementos son inferiores a las correspondientes las mallas con elementos de tamaño uniforme y de alto orden. Por otra parte, las propiedades mecánicas no homogéneas reducen la diferencia en el cálculo de las tensiones. CONCLUSIONES: para obtener modelos específicos al paciente confiables se recomienda, generar la geometría del hueso con superficies suavisadas, controlar la calidad de la malla superficial, usar propiedades mecánicas no homogéneas, y utilizar la malla generada directo en Abaqus con elementos de bajo orden y tamaño no uniforme.

INTRODUCTION: finite element analysis is used to understand and predict biological processes. In orthopedic biomechanics patient specific models are generated by computed tomography and used for medical decision making. Some corrective orthopedic processes may be simulated by means of finite element analysis. In order to obtain reliable biomechanical models it is highly advisable to reduce the number of errors in the definition of the model during pre-processing of the finite element analysis. OBJECTIVE: analyze the influence of mesh density and mechanical properties on the results obtained by finite element analysis during the stage of definition of the patient specific model. METHODS: the finite element method was used to simulate tibial compression. The geometry of the patient's tibia was generated by computed tomography. Meshes were used with non-uniform and uniform element sizes. Homogeneous and non-homogeneous mechanical properties were applied to the model. RESULTS: low-order elements converge to the solution. Tensions for meshes with these elements are lower than those for meshes with uniform size and high-order elements. On the other hand, non-homogeneous mechanical properties reduce the difference in the estimation of tensions. CONCLUSIONS: to obtain reliable patient specific models it is recommended to generate the bone geometry with softened surfaces, control the quality of the surface mesh, use non-homogeneous mechanical properties, and use the mesh generated directly on Abaqus with low-order elements and non-uniform size.

Estudio biomecánico hueso-implante DHS y fijador externo en la consolidación de la fractura de cadera / Étude biomécanique de la vis-plaque dynamique (DHS) et du fixateur externe dans la consolidation de la fracture de hanche / Biomechanical study of bone-DHS implant and external fixator in hip fracture

Objetivos: determinar el comportamiento biomecánico de los conjuntos placa Dinámic Hip Screw-hueso y fijador externo monolateral-hueso y la influencia de estos en la distribución del estado tensional, antes, durante y después de retirado el implante. Métodos: se realizó el estudio aplicando el método de los elementos finitos, se tuvo en cuenta la acción de los músculos y el peso corporal en la fase monopodal del ciclo de marcha, así como las propiedades anisotrópicas en el tejido cortical, e isotrópicas para la parte esponjosa del hueso. Se ejecutó un estudio comparativo del estado tensional del implante y su influencia en la variación del estado tensional-deformacional del hueso, durante el tiempo en que se mantiene el implante en este y luego de ser retirado Resultados: se obtuvo la variación porcentual de las zonas sometidas a tracción y compresión en el hueso sano durante el estado de carga correspondiente a la marcha monopodal, el valor de las tensiones actuantes en cada elemento de los implantes analizados durante la consolidación de la fractura, así como la influencia de estos en la distribución del estado tensional del hueso, durante su funcionamiento y después de retirado el implante. Conclusiones: en relación con el comportamiento mecánico del implante Dinámic Hip Screw y el fijador externo, la situación más desfavorable la presenta el primero, al mostrar tensiones por encima del límite elástico del material en el tornillo inferior de fijación al hueso. Se nota en ambos casos una ligera variación del estado tensional del hueso después de haberse colocado el implante. Al retirar los implantes se produjo una elevación de las tensiones de compresión en los bordes de los agujeros que fijaban uno y otro implante(AU)

Objective: to determine the biomechanical behavior of the bone-Dynamic Hip Screw plate and the bone- monolateral external fixator sets and their influence on the distribution of stress before, during and after the removal of implant. Methods: the study was based on the finite element model, taking into account the muscle actions and the body weight at the monopodal phase of the gait cycle as well as the anisotropic properties of the cortical tissue and the isotropic properties of the spongy part of the bone. A comparative study was also conducted on the stress condition of the implant and its influence over changes in the stress-deformation condition of the bone as long as the implant remains in the bone and after being removed. Results: the variation percentage of the areas under traction and compression in the healthy bone was estimated for the loading condition in the monopodal gait along with the acting stresses in each element of the implants analyzed during the consolidation of fracture and the their influence in the distribution of stresses in the bone during the functioning of implant and after its removal. Conclusions: regarding the mechanical behavior of the Dynamic Hip Screw implant and the external fixator, the most unfavorable situation was found in the first system since stresses were greater than the material's elastic limit in the lower fixation screw. A slight variation of the bone stress was noticed after placing the implant. When both implants were removed, there was a rise of compressive stresses at the borders of the holes they fixed(AU)

Objectif: le but de cette étude est de déterminer le comportement biomécanique de la vis-plaque dynamique (DHS) et du fixateur externe unilatéral, et l'influence de ceux-ci sur la distribution de la tension avant, pendant et après l'enlèvement de l'implant. Méthodes: une étude a été réalisée en utilisant la méthode des éléments finis. On a tenu compte de l'action des muscles et du poids corporel dans la phase d'appui de la marche, ainsi que des propriétés anisotropiques du tissu cortical et isotropiques du corps spongieux de l'os. Une étude comparative de la tension de l'implant et son influence sur la variation de tension et de déformation de l'os avant et après son enlèvement, est effectuée. Résultats: on a obtenu une variation des pourcentages entre les zones soumises à traction et celles soumises à compression de l'os sain au cours de l'état de charge correspondant à la phase d'appui de la marche; un taux des tensions agissant sur chaque élément des implants analysés pendant la consolidation de la fracture, ainsi que leur influence sur la distribution de l'état de tension de l'os au cours son fonctionnement et après l'enlèvement de l'implant. Conclusions: par rapport au comportement mécanique de la vis-plaque dynamique (DHS) et du fixateur externe, on peut conclure que la situation la plus défavorable est présentée par la DHS, dû à ses tensions surmontant la limite élastique du matériel de la vis inférieure de fixation à l'os. Dans tous les deux, on peut constater une légère variation de la tension de l'os après le placement de l'implant. Une fois que les implants sont enlevés, les tensions de compression sur les bords des trous de fixation s'élèvent(AU)

Feasibility of finite element analysis in the application of quality inspection on implantable medical devices / 医用生物力学

For implantable medical devices, traditional mechanical property testing is achieved by mechanical testing devices, while such method is lack of pertinence during sampling of series of products, and also time consuming during experimental testing. With the complete development of finite element analysis (FEA) techniques, introducing FEA to quality supervision and inspection will become a scientific method for saving resources and time, and also improve the pertinence. In this study, the creditability of FEA in application of highest risk sample selection, failure analysis of marketed products and auxiliary optimization of fatigue test testing was verified through case study and experimental testing. The feasibility of FEA during implants inspection was illustrated. In order to ensure the accuracy and reliability of FEA in the application of implants inspection, the essentials of establishing related finite element standards were proposed.

Empleo de elementos finitos en un estudio comparativo de dos sistemas de fijación interna para la fractura de cadera / Emploi des éléments finis dans une étude comparative de deux systèmes de fixation interne pour la fracture de hanche / Use of finite elements in a comparative study of two internal fixation systems for hip fractures

Introducción: existe una gran variedad de sistemas de fijación interna para el tratamiento de las fracturas, por lo que es común que un fijador pueda ser utilizado en diferentes fracturas. Esto trae consigo, que no se sepa con exactitud cuál de los sistemas de fijación interna tendrá mejor comportamiento desde el punto de vista del estado tensional. Objetivo: analizar mediante elementos finitos, el comportamiento de los dispositivos de fijación interna placa DHS y placa a compresión dinámica, utilizados en el tratamiento de las fracturas de cadera. Métodos: el modelo de fémur se obtuvo con autorización del reservorio de modelos óseos del cuerpo humano: The finite element meshes repository of the international society of biomechanics y luego, una tomografía axial computarizada. En los cálculos, se tuvieron en cuenta la acción muscular y el peso corporal en la fase monopodal del ciclo de la marcha, se determinó el estado tensional y el número de ciclos en que los sistemas de fijación interna causaron fallas por fatiga. Resultados: los resultados más desfavorables se encontraron en la placa a compresión dinámica angulada a 130º ya que se alcanzaron los valores de tensiones más altos y el número de ciclos más bajo. Conclusiones: la placa a compresión dinámica angulada a 130º sufre roturas con frecuencia, de ahí que es conveniente utilizar la placa DHS en el tratamiento de la fractura de cadera 31B2.1, siempre que sea posible desde el punto de vista clínico(AU)

Introduction: due to the wide variety of internal fixation systems for the treatment of fractures, it is common practice that the same fixator is used for various fracture types. As a result, it is difficult to tell which of the internal fixation systems will perform better in terms of tensional status. Objective: applying the finite-element method, analyze the behavior of the internal fixation devices DHS plate and dynamic compression plate, used in the treatment of hip fractures. Methods: the model femur was obtained with authorization by the human bone model repository (International Society of Biomechanics FiniteElement Mesh Repository), and studied by computerized axial tomography. Estimations took into account both muscle action and body weight in the monopodal phase of the gait cycle. Determination was made of the tensional status and the number of cycles undergoing fatigue failure. Results: the most unfavorable results corresponded to the 130º-angled dynamic compression plate, which exhibited the highest tension values and the smallest number of cycles. Conclusions: the 130º-angled dynamic compression plate frequently breaks. Hence the advisability of using the DHS plate in the treatment of 31B2.1 hip fractures whenever it is clinically possible(AU)

Introduction: Il y a plusieurs systèmes de fixation interne pour la traitement des fractures, c'est pourquoi l'utilisation de fixateurs est très fréquente. Cela provoque des doutes au moment de choisir le système de fixation interne le plus efficace du point de vue tensionnel. Objectif: Le but de cette étude est d'analyser au moyen des éléments finis le comportement des appareils de fixation interne, tels que la plaque DHS (Dynamic Hip Screw) et la plaque à compression dynamique, utilisés dans le traitement des fracture de hanche. Méthodes: Le modèle du fémur est obtenu sous l'autorisation du réservoir de modèles osseux du corps humain: The finite element meshes repository of the International Society of Biomechanics, et puis une tomographie axiale informatisée. Dans les estimations, l'action musculaire et le poids corporel sont tenus en considération dans la phase d'appui du cycle de la marche, et l'état de tension et le nombre de cycles provoquant l'échec à cause de la fatigue sont déterminés. Résultats: La plaque à compression dynamique sous angle de 130° a eu les résultats les plus défavorables, puisque les valeurs de tension ont été les plus hautes et le nombre de cycles le plus bas. Conclusions: La plaque à compression dynamique sous angle de 130° se brise fréquemment, c'est pourquoi la plaque DHS est conseillée, dès que possible, dans le traitement clinique de la fracture de hanche 31B2.1(AU)

Avaliação do comportamento mecânico de três diferentes tipos de osteossíntese em fratura de côndilo mandibular: análise por elementos finitos 3D / Evaluation of the mechanical behavior of three types of osteosynthesis in fractures of the mandibular condyle: 3D finite element analysis

O uso de duas miniplacas retas é o método mais indicado na literatura, para se prevenir complicações no tratamento de fraturas de côndilo. Diferentes estudos evidenciam que a estabilidade da osteossíntese é relacionada com as tensões mecânicas que ocorrem na região do côndilo, geradas pelos músculos da mastigação. O objetivo neste estudo foi avaliar o comportamento mecânico de três métodos de osteossíntese, por meio de um modelo mandibular de elementos finitos (MEF), comparando a distribuição de tensões e o comportamento dos materiais nas fraturas subcondilares baixas. Simulou-se uma fratura transversa subcondilar baixa, no modelo mandibular e a adaptação dos materiais de osteossíntese para a fixação da fratura. Três métodos de fixação com placas de titânio foram testados: 1) duas placas retas; 2) uma placa lambda e 3) uma placa trapezoidal. Os resultados mostraram que os métodos de osteossíntese proporcionam uma boa rigidez ao sistema de fixação, com pouco deslocamento na linha de fratura. Apesar disto, com a intensidade da força aplicada, todos os modelos estariam sujeitos a falhas, pois apresentaram valores de tensão de von Mises muito elevados. Comparando o desempenho dos três modelos de placas testados, observou-se que, a placa lambda se comportou melhor, havendo uma distribuição das tensões de von Mises sobre o material de fixação e tensão máxima principal sobre o osso mais homogênea

The use of two straight plates is the most indicated in literature, to prevent the subcondilar fractures complications. Different studies have highlighted that the osteosynthesis stability is related to the mechanical stresses that occur in the region of the condyle, generated by the chewing muscles. This study evaluated the biomechanical behavior of three methods of fixation, through a mandibular finite element model (FEM), comparing the stress distribution and behavior of materials in low subcondilar fractures. A transverse fracture was simulated in the mandibular model and on adapting osteosynthesis materials for fracture fixation. Three methods of fixations using titanium plates were tested: two straight plates; one lambda plate and; one trapezoidal plate. The results showed that the method of osteosynthesis provides a good stiffness on the fixation system with little displacement at the fracture line. Nevertheless, by the intensity of the applied force, all models would be subject to failure, because they presented very high stress values. Comparing the performance of the three plate's models tested, it was observed better behaviors for the lambda plate, with a more homogeneous distribution of von Mises stresses on the osteosynthesis devices and maximum principal strain over the bone

Influence from different assigned gradients of material attributes on mechanical properties of the vertebral finite element mode / 医用生物力学

Objective To study the influence from different assigned gradients of material attributes on mechanical properties of the vertebral finite element model. Methods An adult human spine (T12-L5) was CT scanned, and the 3D models of each vertebra were reconstructed in MIMICS, which were then modified in Geomagic and imported into ANSYS for meshing. The element models were imported back to MIMICS and assigned with material properties by separating into 8 kinds of gradients (2, 4, 8, 10, 50, 100, 200, 400 divisions). These models were then imported to ANSYS again for finite element analysis under the same loading condition. Results Significant differences were found in stresses from models with 2, 4, 400 gradients, but the deviations between 8, 10, 50, 100, 200 gradients were not obvious. Conclusions The material attributes of finite element model should be appropriate, and the assigned gradient of 10 divisions could be better guarantee the accuracy of calculation and enhance the calculation speed as well, which is suitable for personalized rapid finite element modeling in clinic.

Modelado computacional del desarrollo óseo humano en la placa de crecimiento del fémur distal / Computational modeling of human bone development in the distal femoral growth plate

La elongación de los huesos largos se produce principalmente por la proliferación e hipertrofia de los condrocitos presentes en las placas de crecimiento. Bajo la hipótesis que el comportamiento de estas células depende de factores bioquímicos y mecánicos, este artículo presenta un modelo computacional por elementos finitos que simula el comportamiento de la placa de crecimiento del fémur distal humano. Se emplea un dominio bidimensional en el que se identifican las regiones de hueso trabecular metafisial y episifial que encierran a la placa de crecimiento y las regiones de cartílago inerte y columnar. La validación del modelo se realiza a partir de la histología correspondiente a la placa de crecimiento del fémur distal de un niño de dos años. Los resultados obtenidos demuestran que el modelo simula el crecimiento y el comportamiento de la placa metafisiaria regulada por su actividad celular y las cargas mecánicas...

Long bone elongation is mainly due to proliferation and hypertrophy of the chondrocytes in growth plates. Under the assumption that the behavior of these cells depends on biochemical and mechanical factors, a presentation is made of a computational finite element model simulating the behavior of the human distal femoral growth plate. A two-dimensional domain is used to identify the regions of metaphyseal and epiphyseal trabecular bone covering the growth plate and the inert and columnar cartilage regions. Model validation was based on the histology corresponding to the distal femoral growth plate of a two-year old boy. The results obtained show that the model simulates the growth and behavior of the metaphyseal plate as regulated by its cellular activity and mechanical loads...