Estudo da distribuição das tensões provenientes de molas helicoidais utilizadas na verticalização de molares pelo método da Fotoelasticidade de transmissão plana

Pós-graduação em Odontologia - FOA

Análise estrutural de juntas rebitadas de uso aeronaútico

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influência dos sistemas de retenção e da inclinação do rebordo residual em casos de próteses conjugadas Classe I mandibular: análise da distribuição das tensões pelo método da fotoelasticidade

Pós-graduação em Odontologia - FOA

Análise das tensões geradas durante a contração de polimerização e aplicação de cargas em restaurações diretas de resina composta. Efeito da utilização de materiais para base ou forramento

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise fotoelástica da distribuição de tensão de diferentes materiais de revestimento oclusal em prótese protocolo do tipo Branemark

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo das tensões em próteses sobre implantes esplintadas: análise pelo método da fotoelasticidade

Pós-graduação em Odontologia - FOA

Photoelastic Analysis of Stress Distribution With Different Implant Systems

The aim of this study was to evaluate stress distribution with different implant systems through photoelasticity. Five models were fabricated with photoelastic resin PL-2. Each model was composed of a block of photoelastic resin (10 x 40 x 45 mm) with an implant and a healing abutment: model 1, internal hexagon implant (4.0 X 10 mm; Conect AR, Conexao, Sao Paulo, Brazil); model 2, Morse taper/internal octagon implant (4.1 x 10 mm; Standard, Straumann ITI, Andover, Mass); model 3, Morse taper implant (4.0 x 10 mm; AR Morse, Conexao); model 4, locking taper implant (4.0 x 11 mm; Bicon, Boston, Mass); model 5, external hexagon implant (4.0 x 10 mm; Master Screw, Conexao). Axial and oblique load (45) of 150 N were applied by a universal testing machine (EMIC-DL 3000), and a circular polariscope was used to visualize the stress. The results were photographed and analyzed qualitatively using Adobe Photoshop software. For the axial load, the greatest stress concentration was exhibited in the cervical and apical thirds. However, the highest number of isochromatic fringes was observed in the implant apex and in the cervical adjacent to the load direction in all models for the oblique load. Model 2 (Morse taper, internal octagon, Straumann ITI) presented the lowest stress concentration, while model 5 (external hexagon, Master Screw, Conexao) exhibited the greatest stress. It was concluded that Morse taper implants presented a more favorable stress distribution among the test groups. The external hexagon implant showed the highest stress concentration. Oblique load generated the highest stress in all models analyzed.

Use of Stress Analysis Methods to Evaluate the Biomechanics of Oral Rehabilitation With Implants

Because the biomechanical behavior of dental implants is different from that of natural tooth, clinical problems may occur. The mechanism of stress distribution and load transfer to the implant/bone interface is a critical issue affecting the success rate of implants. Therefore, the aim of this study was to conduct a brief literature review of the available stress analysis methods to study implant-supported prosthesis loading and to discuss their contributions in the biomechanical evaluation of oral rehabilitation with implants. Several studies have used experimental, analytical, and computational models by means of finite element models (FEM), photoelasticity, strain gauges and associations of these methods to evaluate the biomechanical behavior of dental implants. The FEM has been used to evaluate new components, configurations, materials, and shapes of implants. The greatest advantage of the photoelastic method is the ability to visualize the stresses in complex structures, such as oral structures, and to observe the stress patterns in the whole model, allowing the researcher to localize and quantify the stress magnitude. Strain gauges can be used to assess in vivo and in vitro stress in prostheses, implants, and teeth. Some authors use the strain gauge technique with photoelasticity or FEM techniques. These methodologies can be widely applied in dentistry, mainly in the research field. Therefore, they can guide further research and clinical studies by predicting some disadvantages and streamlining clinical time.

Stress distribution around osseointegrated implants with different internal-cone connections: photoelastic and finite element analysis

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Analysis of residual stress and hardness in regions of pre-manufactured and manual bends in fixation plates for maxillary advancement

The aim of this study was to analyze, through Vickers hardness test and photoelasticity analysis, pre-bent areas, manually bent areas, and areas without bends of 10-mm advancement pre-bent titanium plates (Leibinger system). The work was divided into three groups: group I-region without bend, group II-region of 90° manual bend, and group III-region of 90° pre-fabricated bends. All the materials were evaluated through hardness analysis by the Vickers hardness test, stress analysis by residual images obtained in a polariscope, and photoelastic analysis by reflection during the manual bending. The data obtained from the hardness tests were statistically analyzed using ANOVA and Tukey's tests at a significance level of 5 %. The pre-bent plate (group III) showed hardness means statistically significantly higher (P < 0.05) than those of the other groups (I-region without bends, II-90° manually bent region). Through the study of photoelastic reflection, it was possible to identify that the stress gradually increased, reaching a pink color (1.81 δ / λ), as the bending was performed. A general analysis of the results showed that the bent plate region of pre-bent titanium presented the best results.

Influência do aumento do comprimento de implantes dentários

The use of implants of greater length may be more favorable for the predictability of dental implants. This statement is relevant, since the cause of failures in dental implants are more related to biomechanical complications. The aim of this study was to evaluate the influence of increase of the length around the entire body of the implant. Six models were created with the presence of only one hexagonal implant (Master Screw connection, Implant Systems, São Paulo, Brazil) of 3.75 mm x 7.0 mm (Model A), 3.75 mm x 8.5 mm (Model B ), 3.75 mm x 10.0 mm (Model C) 3.75 mm x 11.5 mm (Model D) 3.75 mm x 13.0 mm (Model E) 3.75 mm x 15.0 mm (Model F) using the method of photoelasticity. The results were visualized through a qualitative analysis of stresses (number and intensity photoelastic fringes). The model A showed a pattern of less favorable stress distribution, the oblique loading was the most detrimental to the related structures. Conclusion: The increased length allowed for a better distribution of stresses. The oblique loading was more detrimental when compared to axial loading.

Influência da angulação do implante e tipo de intermediário na distribuição das tensões

The aim of this study was to evaluate the influence of implant angulation and abutment type (UCLA and Estheticone) on stress distribution in screw-retained implant-supported prostheses through photoelasticity. Three models were fabricated with photoelastic resin PL-2 (Vishay, Micro-Measurements Group, Inc Raleigh, N.C., USA) containing one external hexagon implant with 3.75x10mm (Master screw, Conexão Sistemas de Prótese Ltda., Arujá, São Paulo) with 0°, 17° and 30° degrees and a screw-retained prostheses with UCLA and Estheticone abutments. The assembly was positioned in a circular polariscope; axial and oblique (45° degrees) loads of 100N were applied in fixed points on the occlusal crown surfaces by a universal testing machine. The stress generated was photographed and analyzed qualitatively with appropriate software (Adobe Photoshop®). The results demonstrated the same number of fringes for both abutment types for each angulation, with fringes increasing in the same way. A higher number of fringes were closer in the oblique loading mode. It was concluded that there was no significant difference in stress distribution in prostheses with UCLA and Estheticone abutments. Higher stress concentrations were observed with increased implant angulation. Stress concentration and intensity were higher in the oblique load than in axial load application.

PHOTOELASTIC ANALISYS IN THE LOWER REGION OF VERTEBRAL BODY L4

Objective: To analyze the shear forces on the vertebral body L4 when submitted to a compression force by means of transmission photoelasticity. Methods: Twelve photoelastic models were divided into three groups, with four models per group, according to the positioning of the sagittal section vertebrae L4-L5 (sections A, B and C). The simulation was performed using a 15N compression force, and the fringe orders were evaluated in the vertebral body L4 by the Tardy compensation method. Results: Photoelastic analysis showed, in general, a homogeneous distribution in the vertebral bodies. The shear forces were higher in section C than B, and higher in B than A. Conclusion: The posterior area of L4, mainly in section C, showed higher shear concentrations, corresponding to a more susceptible area for bone fracture and spondylolisthesis. Economic and Decision Analyses Development of an Economic or Decision Model. Level I

Effect of sample pre-cracking method and notch geometry in plane strain fracture toughness tests as applied to a PMMA resin

The influence of test method factors (notch shape, square or angular, and pre-cracking method, by tapping onto or pressing a razor blade) on the results obtained in plane strain fracture toughness test according to standard ASTM D5045 using SENB specimens made of a commercial PMMA resin were investigated. Results were analyzed quantitatively by comparing the obtained K-IC values and qualitatively by observing their effect on the Moire fringes observed using photoelasticity, showing that, at 95% significance level, the K-IC values are affected by the pre-cracking method, with the most conservative value being obtained when natural pre-cracks were introduced by tapping onto a razor blade (K-IC = 1.15 +/- 0.11 MPa.m(0.5)). This correlates with a perturbation in the stress field close to the pre-crack tip observed in the photoelasticity test sample when it was introduced by pressing the razor blade. Surprisingly, notch geometry only slightly affects the results. (C) 2012 Elsevier Ltd. All rights reserved.

Análisis de micromovilidad en vástagos femorales mediante ensayo dinámico de oscilaciones libres

La artroplastia de cadera se considera uno de los mayores avances quirúrgicos de la Medicina. La aplicación de esta técnica de Traumatología se ha incrementado notablemente en los últimos anos, a causa principalmente del progresivo incremento de la esperanza de vida. En efecto, con la edad aumentan los problemas de artrosis y osteoporosis, enfermedades típicas de las articulaciones y de los huesos que requieren en muchos casos la sustitución protésica total o parcial de la articulación. El buen comportamiento funcional de una prótesis depende en gran medida de la estabilidad primaria, es decir, el correcto anclaje de la prótesis en el momento de su implantación. Las prótesis no cementadas basan su éxito a largo plazo en la osteointegración que tiene lugar entre el material protésico y el tejido óseo, y para lograrla es imprescindible conseguir unas buenas condiciones de estabilidad primaria. El aflojamiento aséptico es la principal causa de fallo de artroplastia total de cadera. Este es un fenómeno en el que, debido a complejas interacciones de factores mecánicos y biológicos, se producen movimientos relativos que comprometen la funcionalidad del implante. La minimización de los correspondientes danos depende en gran medida de la detección precoz del aflojamiento. Para lograr la detección temprana del aflojamiento aséptico del vástago femoral se han ensayado diferentes técnicas, tanto in vivo como in vitro: análisis numéricos y técnicas experimentales basadas en sensores de movimientos provocados por cargas transmitidas natural o artificialmente, tales como impactos o vibraciones de distintas frecuencias. Los montajes y procedimientos aplicados son heterogéneos y, en muchas ocasiones, complejos y costosos, no existiendo acuerdo sobre una técnica simple y eficaz de aplicación general. Asimismo, en la normativa vigente que regula las condiciones que debe cumplir una prótesis previamente a su comercialización, no hay ningún apartado referido específicamente a la evaluación de la bondad del diseño del vástago femoral con respecto a la estabilidad primaria. El objetivo de esta tesis es desarrollar una metodología para el análisis, in vitro, de la estabilidad de un vástago femoral implantado, a fin de poder evaluar las técnicas de implantación y los diferentes diseños de prótesis previamente a su oferta en el mercado. Además se plantea como requisito fundamental que el método desarrollado sea sencillo, reversible, repetible, no destructivo, con control riguroso de parámetros (condiciones de contorno de cargas y desplazamientos) y con un sistema de registro e interpretación de resultados rápido, fiable y asequible. Como paso previo, se ha realizado un análisis cualitativo del problema de contacto en la interfaz hueso-vástago aplicando una técnica optomecánica del campo continuo (fotoelasticidad). Para ello se han fabricado tres modelos en 2D del conjunto hueso-vástago, simulando tres tipos de contactos en la interfaz: contacto sin adherencia y con holgura, contacto sin adherencia y sin holgura, y contacto con adherencia y homogéneo. Aplicando la misma carga a cada modelo, y empleando la técnica de congelación de tensiones, se han visualizado los correspondientes estados tensionales, siendo estos más severos en el modelo de unión sin adherencia, como cabía esperar. En todo caso, los resultados son ilustrativos de la complejidad del problema de contacto y confirman la conveniencia y necesidad de la vía experimental para el estudio del problema. Seguidamente se ha planteado un ensayo dinámico de oscilaciones libres con instrumentación de sensores resistivos tipo galga extensométrica. Las muestras de ensayo han sido huesos fémur en todas sus posibles variantes: modelos simplificados, hueso sintético normalizado y hueso de cadáver, seco y fresco. Se ha diseñado un sistema de empotramiento del extremo distal de la muestra (fémur) con control riguroso de las condiciones de anclaje. La oscilación libre de la muestra se ha obtenido mediante la liberación instantánea de una carga estética determinada y aplicada previamente, bien con una maquina de ensayo o bien por gravedad. Cada muestra se ha instrumentado con galgas extensométricas convencionales cuya señal se ha registrado con un equipo dinámico comercial. Se ha aplicado un procedimiento de tratamiento de señal para acotar, filtrar y presentar las respuestas de los sensores en el dominio del tiempo y de la frecuencia. La interpretación de resultados es de tipo comparativo: se aplica el ensayo a una muestra de fémur Intacto que se toma de referencia, y a continuación se repite el ensayo sobre la misma muestra con una prótesis implantada; la comparación de resultados permite establecer conclusiones inmediatas sobre los efectos de la implantación de la prótesis. La implantación ha sido realizada por un cirujano traumatólogo utilizando las mismas técnicas e instrumental empleadas en el quirófano durante la práctica clínica real, y se ha trabajado con tres vástagos femorales comerciales. Con los resultados en el dominio del tiempo y de la frecuencia de las distintas aplicaciones se han establecido conclusiones sobre los siguientes aspectos: Viabilidad de los distintos tipos de muestras sintéticas: modelos simplificados y fémur sintético normalizado. Repetibilidad, linealidad y reversibilidad del ensayo. Congruencia de resultados con los valores teóricos deducidos de la teoría de oscilaciones libres de barras. Efectos de la implantación de tallos femorales en la amplitud de las oscilaciones, amortiguamiento y frecuencias de oscilación. Detección de armónicos asociados a la micromovilidad. La metodología se ha demostrado apta para ser incorporada a la normativa de prótesis, es de aplicación universal y abre vías para el análisis de la detección y caracterización de la micromovilidad de una prótesis frente a las cargas de servicio. ABSTRACT Total hip arthroplasty is considered as one of the greatest surgical advances in medicine. The application of this technique on Traumatology has increased significantly in recent years, mainly due to the progressive increase in life expectancy. In fact, advanced age increases osteoarthritis and osteoporosis problems, which are typical diseases of joints and bones, and in many cases require full or partial prosthetic replacement on the joint. Right functional behavior of prosthesis is highly dependent on the primary stability; this means it depends on the correct anchoring of the prosthesis at the time of implantation. Uncemented prosthesis base their long-term success on the quality of osseointegration that takes place between the prosthetic material and bone tissue, and to achieve this good primary stability conditions is mandatory. Aseptic loosening is the main cause of failure in total hip arthroplasty. This is a phenomenon in which relative movements occur, due to complex interactions of mechanical and biological factors, and these micromovements put the implant functionality at risk. To minimize possible damage, it greatly depends on the early detection of loosening. For this purpose, various techniques have been tested both in vivo and in vitro: numerical analysis and experimental techniques based on sensors for movements caused by naturally or artificially transmitted loads, such as impacts or vibrations at different frequencies. The assemblies and methods applied are heterogeneous and, in many cases, they are complex and expensive, with no agreement on the use of a simple and effective technique for general purposes. Likewise, in current regulations for governing the conditions to be fulfilled by the prosthesis before going to market, there is no specific section related to the evaluation of the femoral stem design in relation to primary stability. The aim of this thesis is to develop a in vitro methodology for analyzing the stability of an implanted femoral stem, in order to assess the implantation techniques and the different prosthesis designs prior to its offer in the market. We also propose as a fundamental requirement that the developed testing method should be simple, reversible, repeatable, non-destructive, with close monitoring of parameters (boundary conditions of loads and displacements) and with the availability of a register system to record and interpret results in a fast, reliable and affordable manner. As a preliminary step, we have performed a qualitative analysis of the contact problems in the bone-stem interface, through the application of a continuous field optomechanical technique (photoelasticity). For this proposal three 2D models of bone–stem set, has been built simulating three interface contact types: loosened an unbounded contact, unbounded and fixed contact, and bounded homogeneous contact. By means of applying the same load to each model, and using the stress freezing technique, it has displayed the corresponding stress states, being more severe as expected, in the unbounded union model. In any case, the results clearly show the complexity of the interface contact problem, and they confirm the need for experimental studies about this problem. Afterward a free oscillation dynamic test has been done using resistive strain gauge sensors. Test samples have been femur bones in all possible variants: simplified models, standardized synthetic bone, and dry and cool cadaveric bones. An embedding system at the distal end of the sample with strong control of the anchoring conditions has been designed. The free oscillation of the sample has been obtained by the instantaneous release of a static load, which was previously determined and applied to the sample through a testing machine or using the gravity force. Each sample was equipped with conventional strain gauges whose signal is registered with a marketed dynamic equipment. Then, it has applied a signal processing procedure to delimit, filter and present the time and frequency response signals from the sensors. Results are interpreted by comparing different trials: the test is applied to an intact femur sample which is taken as a reference, and then this test is repeated over the same sample with an implanted prosthesis. From comparison between results, immediate conclusions about the effects of the implantation of the prosthesis can be obtained. It must be said that the implementation has been made by an expert orthopedic surgeon using the same techniques and instruments as those used in clinical surgery. He has worked with three commercial femoral stems. From the results obtained in the time and frequency domains for the different applications the following conclusions have been established: Feasibility of the different types of synthetic samples: simplified models and standardized synthetic femur. Repeatability, linearity and reversibility of the testing method. Consistency of results with theoretical values deduced from the bars free oscillations theory. Effects of introduction of femoral stems in the amplitude, damping and frequencies of oscillations Detection of micromobility associated harmonics. This methodology has been proved suitable to be included in the standardization process of arthroplasty prosthesis, it is universally applicable and it allows establishing new methods for the analysis, detection and characterization of prosthesis micromobility due to functional loads.