Hybrid surface implants: Influence of residual stress on mechanical behavior, evaluated by finite element analysis and validation by fatigue tests.

OBJECTIVES: To determine the influence of different surface roughness and residual stress of hybrid surface implants on their behavior and mechanical failure. METHODS: Three types of implants with different surface roughness were used as specimens: smooth, rough, and hybrid. A diffractometer was used to determine the residual stress of the implants according to their different surface treatment. These results were used as an independent variable in a finite element analysis that compared the three specimens to determine the von Mises stress transferred to the implants and supporting bone and the resulting microdeformations. Flexural strength and fatigue behavior tests were performed to compare the results of the three types of implants. RESULTS: Higher residual stress values were found for rough surfaces (p < 0.05, Student's t-test) compared to smooth surfaces, and both types of stress were different for the two types of hybrid implant surfaces. Finite element analysis found different von Mises stress and microdeformation results, both at the level of the implant and the bone, for the three types of implants under study. These results were correlated with the different flexural strength behaviors (lower resistance for hybrids and higher for rough surfaces, p < 0.05) and fatigue behavior (the rough implant had the longest fatigue life, while the hybrid implant exhibited the worst fatigue behavior). SIGNIFICANCE: The results show a trend toward a less favorable mechanical behavior of the hybrid implants related to the retention of different residual stresses caused by the surface treatment.

A Systematic Study of Restorative Crown-Materials Combinations for Dental Implants: Characterization of Mechanical Properties under Dynamic Loads.

This study aimed to find the optimum mechanical characteristics of the restorative materials for the manufacture of implant crowns subjected to impact loading when different combinations of materials are used for the inner and outer crown. Several combinations of external-internal crown restorative materials were analyzed. The dynamic stresses at eight different zones of a dental implant subjected to an impact load and the influence of several mechanical properties, such as the Young's modulus, Poisson's ratio, density, and initial velocity, were analyzed and compared. A detailed 3D model was created, including the crown, the retention screw, the implant, and a mandible section. The model was then built by importing the 3D geometries from CAD software. The whole 3D model was carefully created in order to guarantee a finite element mesh that produced results adjusted to physical reality. Then, we conducted a numerical simulation using the finite element method (FEM). The results of the FEM analysis allowed for evaluating the effect that different combinations of restorative materials and mechanical properties had on the stress distribution in various regions of the implant. The choice of restorative material is a factor to be considered in order to preserve the integrity of osseointegration. Restorative materials transfer more or less stress to the dental implant and surrounding bone, depending on their stiffness. Therefore, an inadequate Young's modulus of the rehabilitation material can affect the survival of the implant over time. Eight interactive graphics were provided on a web-based surface platform to help clinical dentists, researchers, and manufacturers to select the best restorative materials combination for the crown.

Influence of Bone-Level Dental Implants Placement and of Cortical Thickness on Osseointegration: In Silico and In Vivo Analyses.

The purpose of this research is to study the biomechanical response of dental implants in bone-level type locations, 0.5 mm above and below the bone level. In addition, the influence of the thickness of the cortical bone on osseointegration is determined due to the mechanical loads transfer from the dental implant to the cortical and trabecular bone. The thicknesses studied were 1.5 mm and 2.5 mm. Numerical simulations were performed using a finite element method (FEM)-based model. In order to verify the FEM model, the in silico results were compared with the results obtained from a histological analysis performed in an in vivo study with 30 New Zealand rabbits. FEM was performed using a computerized 3D model of bone-level dental implants inserted in the lower jawbone with an applied axial load of 100 N. The analysis was performed using different distances from the bone level and different thicknesses of cortical bone. The interface area of bone growth was evaluated by analyzing the bone-implant contact (BIC), region of interest (ROI) and total bone area (BAT) parameters obtained through an in vivo histological process and analyzed by scanning electron microscopy (SEM). Bone-level implants were inserted in the rabbit tibiae, with two implants placed per tibia. These parameters were evaluated after three or six weeks of implantation. FEM studies showed that placements 0.5 mm below the bone level presented lower values of stress distribution compared to the other studied placements. The lower levels of mechanical stress were then correlated with the in vivo studies, showing that this position presented the highest BIC value after three or six weeks of implantation. In this placement, vertical bone growth could be observed up the bone level. The smallest thickness of the study showed a better transfer of mechanical loads, which leads to a better osseointegration. In silico and in vivo results both concluded that the implants placed 0.5 mm below the cortical bone and with lower thicknesses presented the best biomechanical and histological behavior in terms of new bone formation, enhanced mechanical stability and optimum osseointegration.

A simple and effective 1D-element discrete-based method for computational bone remodeling.

In-silico models applied to bone remodeling are widely used to investigate bone mechanics, bone diseases, bone-implant interactions, and also the effect of treatments of bone pathologies. This article proposes a new methodology to solve the bone remodeling problem using one-dimensional (1D) elements to discretize trabecular structures more efficiently for 2D and 3D domains. An Euler integration scheme is coupled with the momentum equations to obtain the evolution of material density at each step. For the simulations, the equations were solved by using the finite element method, and two benchmark tests were solved varying mesh parameters. Proximal femur and calcaneus bone were selected as study cases given the vast research available on the topology of these bones, and compared with the anatomical features of trabecular bone reported in the literature. The presented methodology has proven to be efficient in optimizing topologies of lattice structures; It can predict the trend of formation patterns of the main trabecular groups from two different cancellous bones (femur and calcaneus) using domains set up by discrete elements as a starting point. Preliminary results confirm that the proposed approach is suitable and useful in bone remodeling problems leading to a considerable computational cost reduction. Characteristics similar to those encountered in topological optimization algorithms were identified in the benchmark tests as well, showing the viability of the proposed approach in other applications such as bio-inspired design.

Bone Stress Evaluation with and without Cortical Bone Using Several Dental Restorative Materials Subjected to Impact Load: A Fully 3D Transient Finite-Element Study.

Statement of problem. Previous peri-implantitis, peri-implant bone regeneration, or immediate implant placement postextraction may be responsible for the absence of cortical bone. Single crown materials are then relevant when dynamic forces are transferred into bone tissue and, therefore, the presence (or absence) of cortical bone can affect the long-term survival of the implant. Purpose: the purpose of this study is to assess the biomechanical response of dental rehabilitation when selecting different crown materials in models with and without cortical bone. Methods: several crown materials were considered for modeling six types of crown rehabilitation: full metal (MET), metal-ceramic (MCER), metal-composite (MCOM), peek-composite (PKCOM), carbon fiber-composite (FCOM), and carbon fiber-ceramic (FCCER). An impact-load dynamic finite-element analysis was carried out on all the 3D models of crowns mentioned above to assess their mechanical behavior against dynamic excitation. Implant-crown rehabilitation models with and without cortical bone were analyzed to compare how the load-impact actions affect both type of models. Results: numerical simulation results showed important differences in bone tissue stresses. The results show that flexible restorative materials reduce the stress on the bone and would be especially recommendable in the absence of cortical bone. Conclusions: this study demonstrated that more stress is transferred to the bone when stiffer materials (metal and/or ceramic) are used in implant supported rehabilitations; conversely, more flexible materials transfer less stress to the implant connection. Also, in implant-supported rehabilitations, more stress is transferred to the bone by dynamic forces when cortical bone is absent.

Manejo del retropié plano valgo flexible con la férula tipo UCBL en pacientes pedátricos: [revisión] / Management of the flexible flat hindfoot valvus with orthesis type UCBL in pediatric patients: [review]

El tratamiento de las diversas deformidades del pie varia según las patologías y es precisamente en el niño por su gran plasticidad biológica, en quien se pueden aplicar los diferentes resursos que se poseen para el tratamiento ortopédico conservador. En el presente trabajo se plantea una alternativa para el tratamiento del retropié valgo, con la férula termo formada tipo UCBL (University of California Biomechanics Laboratory. Demostrar la utilidad de la férula tipo UCBL en el tratamiento conservador del retropié valgo para postegar y/o evitar tratamientos quirúrgicos por deformidades severas. La muestra utilizada fue de 15 pacientes (6 niñas, 9 niños, con edades entre 2 años 6 meses y 10 años) con disfunción del brazo de palanca por pérdida de la rigidez ósea, debido a la subluxación de la articulación sub-astragalina (retropié valgo flexible), en quienes se utilizó la férula termoformada tipo UCBL con seguimiento promedio de 12 a 36 meses. Se evaluó clínicamente la flexibilidad del pié y la maniobra de Silverskiold y radiologicamente en bípeda estación estática, el ángulo Costa-Bertani, Astrágalo calcáneo y astrágalo-1er metatarsiano. 10 pacientes presentaron mejoría clínica y radiológica, 5 de los casos no evidenciaron cambios, sin embargo, mantuvieron su flexibilidad. La férula resultó útil, inclusive en los casos donde no se demostró corrección radiológica, ya que evitó estructuración de la deformidad.

The adequate treatment for foot deformities varies depending on the pathology, and because of the high plasticity found in children, it is in this age group where the available conservative treatment resources can be applied. An alternative for the valgus hindfoot treatment is presented in this paper, using the UCBL (University of California Biomechanies Laboratory) thermoshaped orthesis. To prove utility of the thermoformed UCBL type orthesis in the treatment of flexible pes valgus in orden to avoid fuseverity deformities. The study included 15 patients (6 female, 9 male, ages between 2 years 6 months and 10 years) with lever-arm dysfunction due to loss of bony rigidity with sub-astragaline joint subluxation (flexible valgus hindfoot), in whom UCBL thermoshaped orthesis was indicated with an average follow up between 12 to 36 monts. Foot flexibility was clinical evaluated; also Silverskiold maneuver and static bipedestation x-rays angles were measured. Ten patients showed clinical and radiological improvement, 5 patients showed no change, although flexibility was maintained. The UCBL orthesis was useful, even in cases were no radiological change was observed, because it avoided structuration of bony deformity.

Diseño y fabricación de una celda de carga para mediciones fisiológicas en distracción alveolar / Design and manufacturing of a load-cell for physiological measuring in alveolar distraction

Un factor de vital importancia para el diseño mecánico de distractor osteogénico alveolar es el conocimiento de las cargas fisiológicas para la simulación computacional, existe muy poca información o trabajos previos sobre este tema. Para obtener estas cargas, ha sido desarrollada una celda de carga constituida de una lámina de acero inoxidable en voladizo instrumentada con galgas extensométricas, la cual ha sido empotrada en una férula como la usada en tratamientos de ortodoncias. Luego de calibrar la celda de cargas fisiológicas, se realizó un ensayo in vivo sobre un paciente parcialmente edéntulo del maxilar inferior, obteniéndose registros digitales de cargas para diferentes condiciones de protrusión de la lengua, retracción del labio inferior y la combinación de ambas.

A key aspect involved in the mechanical design of alveolar distractor is the accurate evaluation of physiological loading for computer simulation. Very few information and previous work are available about this subject. A stainless steel load cell having strain gauges has been developed and manufactured. This cell was attached to a splint, like those used in orthodontia. The load cell was calibrated and then an “in vivo” test was carried out on a partially-edentulous patient. Digital registers of load were obtained for three cases: tongue protrusion, lower lips retraction and a combination of both.

Superposición de singularidades para simular la presencia de cavidades en problemas de elastostática usando el método de los elementos de contorno / Singular superposition technique to simulate cavities in elastostatic problems using boundary element method

Se presenta una solución eficiente usando una técnica de superposición de cargas puntuales en elastostática empleando el método de elementos de contorno. La superposición de un conjunto de cargas puntuales para simular la presencia de cavidades ofrece una ventaja en la reducción del tiempo computacional en problemas de elastostática; el uso del método de elementos de contorno optimiza el proceso ya que no se requiere re-discretizar el contorno. Se valida la solución en configuraciones geométricas regulares con cavidades simples a partir de resultados obtenidos a través de experimentos numéricos usando el Método de los Elementos de Contorno.

An efficient singular superposition technique in elastostatics boundary element methods for cavity detection using a point load is presented in this paper. The superposition of several concentrated loads to simulate the presence of cavities leads to a significant reduction of the computational time in the elastostatics field solution with the boundary element method since no boundary re-discretization is necessary throughout the optimization process. Results of cavity presence problems simulated using numerical experiments validate the approach in regular geometrical configurations with single cavities.

Descomposición de dominio iterativo en paralelo para problemas termoelásticos 2D usando el método de elementos de contorno / Parallel-iterative domain decomposition for 2D thermoelastic problems using the boundary element method

Para resolver problemas de termoelasticidad con el Método de Elementos de Contorno (MEC) solo se requiere discretizar la superficie; sin embargo las matrices resultantes se caracterizan por no ser diagonalmente dominantes y estar completamente llenas. Esto representa un reto para resolver problemas de gran escala, dado los requerimientos de almacenamiento de datos y la solución de sistemas de gran número de ecuaciones. En este artículo se desarrolla una técnica de descomposición de dominio o multiregiones eficiente y efectiva, con algoritmos iterativos región por región, ensamblados especialmente para paralelismo computacional. La aproximación de descomposición de dominio efectivamente reduce el número de condiciones de los sistemas de ecuaciones algebraicos resultantes, al mismo tiempo que incrementa la eficiencia de los procesos de solución, convergiendo rápidamente a una solución estable. El paralelismo computacional satisface perfectamente la técnica iterativa de la descomposición de dominio. Los resultados demuestran la calidad de la aproximación al comparar con las soluciones de problemas en una región y las respectivas soluciones analíticas.

The Boundary Element Method (BEM) requires only a surface mesh to solve thermoelasticity problems. However, the resulting matrices are fully populated and non-diagonally dominant. This poses serious challenges for large-scale problems due to storage requirements and the solution of large sets of non-symmetric systems of equations. In this article, an effective and efficient domain decomposition, or artificial sub-sectioning technique, along with a region-by-region iteration algorithm particularly tailored for parallel computation to address these issues is developed. The domain decomposition approach effectively reduces the condition numbers of the resulting algebraic systems, while increasing efficiency of the solution process and decreasing memory requirements. The iterative process converges very efficiently while offering substantial savings in memory. The iterative domain decomposition technique is ideally suited for parallel computation. Results demonstrate the validity of the approach by providing solutions that compare closely to single-region BEM solutions and benchmark analytical solutions.

Operative contractility: a functional concept of the inotropic state.

1. Initial unsuccessful attempts to evaluate ventricular function in terms of the 'heart as a pump' led to focusing on the 'heart as a muscle' and to the concept of myocardial contractility. However, no clinically ideal index exists to assess the contractile state. The aim of the present study was to develop a mathematical model to assess cardiac contractility. 2. A tri-axial system was conceived for preload (PL), afterload (AL) and contractility, where stroke volume (SV) was represented as the volume of the tetrahedron. Based on this model, 'operative' contractility ('OperCon') was calculated from the readily measured values of PL, AL and SV. The model was tested retrospectively under a variety of different experimental and clinical conditions, in 71 studies in humans and 29 studies in dogs. A prospective echocardiographic study was performed in 143 consecutive subjects to evaluate the ability of the model to assess contractility when SV and PL were measured volumetrically (mL) or dimensionally (cm). 3. With inotropic interventions, OperCon changes were comparable to those of ejection fraction (EF), velocity of shortening (Vcf) and dP/dt-max. Only with positive inotropic interventions did elastance (Ees) show significantly larger changes. With load manipulations, OperCon showed significantly smaller changes than EF and Ees and comparable changes to Vcf and dP/dt-max. Values of OperCon were similar when AL was represented by systolic blood pressure or wall stress and when volumetric or dimensional values were used. 4. Operative contractility is a reliable, simple and versatile method to assess cardiac contractility.

Diseño y análisis de placas cervicales anteriores mediante el método de los elementos finitos / Analysis and design of anterior cervical plates using the finite element method

En este trabajo se presenta el diseño y análisis de placas de fijación vertebral, utilizando el método de los elementos finitos. El objetivo de estas placas es devolver estabilidad a la columna vertebral y mejorar la fusión ósea, ofreciendo libertad en el posicionamiento de los tornillos para fijarlas al cuerpo vertebral. Para el diseño geométrico y el análisis fueron utilizados software ProEngineer© y Nastran©. Los esfuerzos que fueron obtenidos del análisis se mantuvieron dentro del rango elástico del material con el cual fueron simulados cada uno de los dos modelos de placas propuestas.

The analysis and design of cervical fixation plates using the finite element method is presented in this paper. Thepurpouse of these plates is to restore stability in the cervical spine and to improve the interbody fusion, allowing different screw positions to attach them to the vertebral body. The geometrical design and discretization were carried out by using ProEngineer© and Nastran© commercial software. The models of the mechanical devices are presented as well as the stress levels produced by the physiological loading. The results obtained from the analysis, showed stresses inside the elastic range in all the studied load cases.

[Bone remodelling using the boundary element method]. / Remodelado óseo utilizando el método de los elementos de contorno.

An algorithm for the mathematical representation of external bone remodeling is proposed. The Boundary element method is used for the numerical analysis of trabecular bone, together with the remodeling algorithm presented by Fridez. The versatility and power of the algorithm discussed herein are shown by some numerical examples. As well, the method converges very fast to the solution, which is one of the main advantages of the proposed numerical scheme.

Remodelado óseo utilizando el método de los elementos de contorno / External bone remode ling using the bound ary element method

Se propone un algoritmo para la simulación matemática del proceso remodelado óseo externo a nivel trabecular. Para ello se realizó el cálculo estructural con el método de los elementos de contorno y se integró con el modelo de remodelación ósea propuesto por Fridez9. Se incluyen varios ejemplos numéricos que muestran la validez y versatilidad del método propuesto. La velocidad en la obtención de la solución es una de las principales ventajas de este método.

An algorithm for the mathematical representation of external bone remodeling is proposed. The Boundary element method is used for the numerical analysis of trabecular bone, together whit the remodeling algorithm presented by Fridez9. The versatility and power of the algorithm discussed herein are shown by some numerical examples. As well, the method converges very fast to the solution, which is one of the main advantages of the proposed numerical scheme

El sistema bloqueado intramedular para el perone distal en las fracturas de tobillo weber "B" / The blockade intramedullary system for the distal fibula in the weber B fractures of human ankle

Se presenta el siguiente estudio prospectivo y comparativo de dos grupos de pacientes tratados con un nuevo clavo intramedular para fracturas Weber B con la placa de tercio de caña, obteniéndose como resultado que no se encontró diferencia estadística en el tratamiento del clavo intramedular en las evaluaciones clínicas. Este sistema de fijación nos ofrece una alternativa válida en el tratamiento de estas lesiones articulares

Fractura de la escápula: análisis biomecánico / Scapula fracture: biomechanics analysis

Se realiza un estudio prospectivo de 5 piezas anatómicas de escápula humana, obteniendose los resultados de las fuerzas actuantes en sus diferentes estructuras, siendo el manguito rotador imprescindible en la biomecánica normal de la articulación del hombro. Asimismo, se determinó la importancia de la escápula como unidad estructural de la misma. Estos hallazgos nos permiten inferir que el tratamiento quirúrgico de las fracturas de la escápula tiene un papel cada vez más importante y que el material de síntesis AO de 3.5 y 2.7 mm es el más idóneo