Biomechanical Fatigue Behavior of a Dental Implant Due to Chewing Forces: A Finite Element Analysis.

The use of titanium as a biomaterial for the treatment of dental implants has been successful and has become the most viable and common option. However, in the last three decades, new alternatives have emerged, such as polymers that could replace metallic materials. The aim of this research work is to demonstrate the structural effects caused by the fatigue phenomenon and the comparison with polymeric materials that may be biomechanically viable by reducing the stress shielding effect at the bone-implant interface. A numerical simulation was performed using the finite element method. Variables such as Young's modulus, Poisson's coefficient, density, yield strength, ultimate strength, and the S-N curve were included. Prior to the simulation, a representative digital model of both a dental implant and the bone was developed. A maximum load of 550 N was applied, and the analysis was considered linear, homogeneous, and isotropic. The results obtained allowed us to observe the mechanical behavior of the dental implant by means of displacements and von Mises forces. They also show the critical areas where the implant tends to fail due to fatigue. Finally, this type of non-destructive analysis proves to be versatile, avoids experimentation on people and/or animals, and reduces costs, and the iteration is unlimited in evaluating various structural parameters (geometry, materials, properties, etc.).

Numerical Analysis of Zirconium and Titanium Implants under the Effect of Critical Masticatory Load.

Dental implants have become an alternative to replace the teeth of people suffering from edentulous and meet the physiological and morphological characteristics (recovering 95% of the chewing function). The evolution and innovation of biomaterials for dental implants have had a trajectory that dates back to prehistory, where dental pieces were replaced by ivory or seashells, to the present day, where they are replaced by metallic materials such as titanium or ceramics such as zirconium or fiberglass. The numerical evaluation focuses on comparing the stress distribution and general displacement between different dental implants and a healthy tooth when applying a force of 850 N. For the analysis, a model of the anatomical structure was developed of a healthy tooth considering three essential parts of the tooth (enamel, dentin, and pulp). The tooth biomodel was established through computed tomography. Three dental implant models were considered by changing the geometry of the abutment. A structural simulation was carried out by applying the finite element method (FEM). In addition, the material considered for the analyses was zirconium oxide (ZrO2), which was compared against titanium alloy (Ti6Al4V). The analyses were considered with linear, isotropic, and homogeneous properties. The variables included in the biomodeling were the modulus of elasticity, Poisson's ratio, density, and elastic limit. The results obtained from the study indicated a significant difference in the biomechanical behavior of the von Mises forces and the displacement between the healthy tooth and the titanium and zirconium implant models. However, the difference between the titanium implant and the zirconium implant is minimal because one is more rigid, and the other is more tenacious.

Traumatic Impact Assessment of CPR Load on a Human Ribcage.

Chest compression is a parameter of injury criteria assessment for human beings. Additionally, it is used to find the external compression response as a result of vehicle crashes, falls, or sporting impacts. This behavioral feature is described by many deterministic models related to specific experimental tests, hindering distinct scenarios. The present study evaluates the energy absorbed as a function of rib compression. The proposed model was obtained from three different computed tomography (CT) studies. The anthropometric values are interpolated to obtain a parametric curve for a human rib's average size. The computed results are compared against an STL-DICOM® file used to obtain a virtual reconstruction of one rib. A numerical model of the behavior of the thorax displacement expressed injury in the human rib model's stiffness. The proposed model is used to determine the correlation of the input payload versus the numerical stiffness value. The outcome is confirmed by numerical analyses applied to a virtual human rib reconstruction.

Redesign of a Piston for a Diesel Combustion Engine to Use Biodiesel Blends.

Biofuels represent an energy option to mitigate polluting gases. However, technical problems must be solved, one of them is to improve the combustion process. In this study, the geometry of a piston head for a diesel engine was redesigned. The objective was to improve the combustion process and reduce polluting emissions using biodiesel blends as the fuel. The methodology used was the mechanical engineering design process. A commercial piston (base piston) was selected as a reference model to assess the piston head's redesign. Changes were applied to the profile of the piston head based on previous research and a new model was obtained. Both models were evaluated and analyzed using the finite element method, where the most relevant physical conditions were temperature and pressure. Numerical simulations in the base piston and the new piston redesign proposal presented similar behaviors and results. However, with the proposed piston, it was possible to reduce the effort and the material. The proposed piston profile presents adequate results and behaviors. In future, we suggest continuing conducting simulations and experimental tests to assess its performance.

Identification of Stress Fields in a Customized Mandibular Reconstruction Based on a Photoelastic Model.

Tumors, trauma and infections are the main reasons for subjecting a patient to a bone reconstruction made with the use of bone grafts or prosthetic elements, using for example components such as osteosynthesis plates, meshes and screws for their stabilization.This study focuses on the photoelastic analysis of a customized prosthesis of the jaw for a patient diagnosed with osteonecrosis. A resin model was manufactured as follows: DICOM files were processed in ScanIP software to obtain an STL file that was used to generate an antagonist model of the healthy section of the jaw using CATIA software, then, models were printed in Acrylonitrile Butadiene Styrene (ABS). Following the resin casting technique, the printed model of the jaw was used to construct a resin model, which is tested to determine its mechanical behavior.After carrying out the photoelastic analysis, it was found that the assembly process generates stress concentration zones. Here, the stress reaches a maximum value after the application of a bite force of 130.9 N in the premolars. In this study near the premolars, 3 stress concentration zones were identified and overlap of stress fields is reveled.The results show the importance of planning in the design and assembly process to obtain the best results in the reconstruction, reducing in this way the risk of a surgical reoperation due to problems of rupture or loosening of the prosthesis.

Diseño mecánico de un exoesqueleto para rehabilitación de miembro superior / Mechanical design of an exoskeleton for upper limb rehabilitation

El ritmo de vida actual, tanto sociocultural como tecnológico, ha desembocado en un aumento de enfermedades y padecimientos que afectan las capacidades físico-motrices de los individuos. Esto ha originado el desarrollo de prototipos para auxiliar al paciente a recuperar la movilidad y la fortaleza de las extremidades superiores afectadas. El presente trabajo aborda el diseño de una estructura mecánica de un exoesqueleto con 4 grados de libertad para miembro superior. La cual tiene como principales atributos la capacidad de ajustarse a la antropometría del paciente mexicano (longitud del brazo, extensión del antebrazo, condiciones geométricas de la espalda y altura del paciente). Se aplicó el método BLITZ QFD para obtener el diseño conceptual óptimo y establecer adecuadamente las condiciones de carga de servicio. Por lo que, se definieron 5 casos de estudio cuasi-estáticos e implantaron condiciones para rehabilitación de los pacientes. Asimismo, mediante el Método de Elemento Finito (MEF) se analizaron los esfuerzos y deformaciones a los que la estructura está sometida durante la aplicación de los agentes externos de servicio. Los resultados presentados en éste trabajo exhiben una nueva propuesta para la rehabilitación de pacientes con problemas de movilidad en miembro superior. Donde el equipo propuesto permite la rehabilitación del miembro superior apoyado en 4 grados de libertad (tres grados de libertad en el hombro y uno en el codo), el cual es adecuado para realizar terapias activas y pasivas. Asimismo, es un dispositivo que está al alcance de un mayor porcentaje de la población por su bajo costo y fácil desarrollo en la fabricación.

The pace of modern life, both socio-cultural and technologically, has led to an increase of diseases and conditions that affect the physical-motor capabilities of persons. This increase has originated the development of prototypes to help patients to regain mobility and strength of the affected upper limb. This work, deals with the mechanical structure design of an exoskeleton with 4 degrees freedom for upper limb. Which has the capacity to adjust to the Mexican patient anthropometry (arm length, forearm extension, geometry conditions of the back and the patient's height) BLITZ QFD method was applied to establish the conceptual design and loading service conditions on the structure. So, 5 quasi-static cases of study were defined and conditions for patient rehabilitation were subjected. Also by applying the finite element method the structure was analyzed due to service loading. The results presented in this work, show a new method for patient rehabilitation with mobility deficiencies in the upper limb. The proposed new design allows the rehabilitation of the upper limb under 4 degrees of freedom (tree degrees of freedom at shoulder and one at the elbow), which is perfect to perform active and passive therapy. Additionally, it is an equipment of low cost, which can be affordable to almost all the country population.