An artificial Neural Network (ANN) system has been developed that can analyse aircraft flight data to provide a reconstruction of the aerodynamic loads experienced by the aircraft during flight, including manoeuvre, buffet and distributed loading. For this research data was taken from the International Follow-On Structural Test Project (IFOSTP) F/A-18 fatigue test conducted by the Royal Australian Air Force and Canadian Forces. This fatigue test involved the simultaneous application of both manouevre and buffet loads using airbag actuators and shakers. The applied loads were representative of the actual loads experienced by an FA/18 during flight tests. Following an evaluation of different ANN types an Ellman network with three linear layers was selected. The Elman back-propagation network was tested with various parameters and structures. The network was trained using the MATLAB 'traingdx' function with is a gradient descent with momentum and adaptive learning rate back-propagation algorithm. The ANN was able to provide a good approximation of the actual manoeuvre or buffet loads at the location where the training loads data were recorded even for input values which differ from the training input values. In further tests the ability to estimate distributed loading at locations not included in the training data was also demonstrated. The ANN was then modified to incorporate various methods for the calculation and prediction of output error and reliability Used in combination and in appropriate circumstances, the addition of these capabilities significantly increase the reliability, accuracy and therefore usefulness of the ANN system's ability to estimate aircraft loading.To demonstrate the ANN system's usefulness as a fatigue monitoring tool it was combined with a formulae for crack growth analysis. Results inficate the ANN system may be a useful fatigue monitoring tool enabling real time monitoring of aircraft critical components using existing strain gauge sensors.

This thesis analyzes and solves the problems of monitoring of constructions strains (small resistance changes) in a number of points of the structure. The essence of investigated systems is test of the strain gauges small resistance changes proportional to displacement or strain and reaching only thousandths of parts of percent. The main objects of research is strain detection circuits working under automatic multipoint balanced Wheatstone bridge and the current balancing methods. The introduction reveals the importance of investigated problem, formulates the aim and tasks, introduces publications and presentations of the author’s and the structure of the dissertation. The first chapter is a review of literature. It analyzes practical use of strain measurement methods, their advantages and disadvantages, opportunities to use these methods in automated systems. The chapter ends with formulated conclusions. The second section presents balanced methods of the strain monitoring. Analysis of balanced Wheatstone bridge device is made. New strain monitoring device by balancing currents are proposed and investigated. There are two possible ways: with two current sources and one current source. The third and fourth sections provide results of computer simulation and experimental models. The proposed devices of balancing currents has been modeled and tested in practice. Stability of the devices was tested and their work simulating in real conditions. Conclusions, references and the... [to full text] / Disertacijoje nagrinėjamos ir sprendžiamos konstrukcijų deformacijų (varžų mažų pokyčių) nustatymo daugelyje konstrukcijos taškų problemos. Tiriamų sistemų funkcionavimo esmė yra įtempių jutiklių varžos mažų pokyčių proporcingų poslinkiui ar deformacijai ir siekiančių tik tūkstantąsias procento dalis nustatymas. Pagrindiniai tyrimo objektai yra automatinių daugiataškių balansuojamo Vitstono tiltelio ir srovių balansavimo metodais veikiantys deformacijų nustatymo grandynai. Įvadiniame skyriuje nagrinėjamas problemos aktualumas, formuluojamas darbo tikslas ir uždaviniai, pristatomi autoriaus pranešimai ir publikacijos, pateikiama disertacijos struktūra. Pirmajame skyriuje pateikta literatūros apžvalga. Jame analizuojami praktikoje naudojami deformacijų nustatymo metodai, pateikiami jų privalumai ir trūkumai, galimybės naudoti šiuos metodus automatizuotose sistemose. Antrajame skyriuje pateikti konstrukcijų deformacijų balansuojami nustatymo būdai. Yra atlikta balansuojamo Vitstono tiltelio metodo analizė. Pateiktas naujas deformacijų stebėjimo balansuojant sroves metodas ir atlikta jo analizė. Jame išskiriami du galimi būdai: su dviem srovės šaltiniais ir su vienu srovės šaltiniu. Trečiajame ir ketvirtajame skyriuose pateikti kompiuterinio modeliavimo ir eksperimentinių tyrimų rezultatai. Buvo sumodeliuotas ir praktiškai patikrintas pasiūlyto srovės balansavimo metodo praktinis veikimas. Patikrintas įrenginių stabilumas ir jų darbas imituojant realias sąlygas. Disertacijos... [toliau žr. visą tekstą]

Disertacijoje nagrinėjamos ir sprendžiamos konstrukcijų deformacijų (varžų mažų pokyčių) nustatymo daugelyje konstrukcijos taškų problemos. Tiriamų sistemų funkcionavimo esmė yra įtempių jutiklių varžos mažų pokyčių proporcingų poslinkiui ar deformacijai ir siekiančių tik tūkstantąsias procento dalis nustatymas. Pagrindiniai tyrimo objektai yra automatinių daugiataškių balansuojamo Vitstono tiltelio ir srovių balansavimo metodais veikiantys deformacijų nustatymo grandynai. Įvadiniame skyriuje nagrinėjamas problemos aktualumas, formuluojamas darbo tikslas ir uždaviniai, pristatomi autoriaus pranešimai ir publikacijos, pateikiama disertacijos struktūra. Pirmajame skyriuje pateikta literatūros apžvalga. Jame analizuojami praktikoje naudojami deformacijų nustatymo metodai, pateikiami jų privalumai ir trūkumai, galimybės naudoti šiuos metodus automatizuotose sistemose. Antrajame skyriuje pateikti konstrukcijų deformacijų balansuojami nustatymo būdai. Yra atlikta balansuojamo Vitstono tiltelio metodo analizė. Pateiktas naujas deformacijų stebėjimo balansuojant sroves metodas ir atlikta jo analizė. Jame išskiriami du galimi būdai: su dviem srovės šaltiniais ir su vienu srovės šaltiniu. Trečiajame ir ketvirtajame skyriuose pateikti kompiuterinio modeliavimo ir eksperimentinių tyrimų rezultatai. Buvo sumodeliuotas ir praktiškai patikrintas pasiūlyto srovės balansavimo metodo praktinis veikimas. Patikrintas įrenginių stabilumas ir jų darbas imituojant realias sąlygas. Disertacijos... [toliau žr. visą tekstą] / This thesis analyzes and solves the problems of monitoring of constructions strains (small resistance changes) in a number of points of the structure. The essence of investigated systems is test of the strain gauges small resistance changes proportional to displacement or strain and reaching only thousandths of parts of percent. The main objects of research is strain detection circuits working under automatic multipoint balanced Wheatstone bridge and the current balancing methods. The introduction reveals the importance of investigated problem, formulates the aim and tasks, introduces publications and presentations of the author’s and the structure of the dissertation. The first chapter is a review of literature. It analyzes practical use of strain measurement methods, their advantages and disadvantages, opportunities to use these methods in automated systems. The chapter ends with formulated conclusions. The second section presents balanced methods of the strain monitoring. Analysis of balanced Wheatstone bridge device is made. New strain monitoring device by balancing currents are proposed and investigated. There are two possible ways: with two current sources and one current source. The third and fourth sections provide results of computer simulation and experimental models. The proposed devices of balancing currents has been modeled and tested in practice. Stability of the devices was tested and their work simulating in real conditions. Conclusions, references and the... [to full text]

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The presented work aims to optimize the performance of piezoresistive cantilevers in cases where the output signal originates either from a static deflection of the cantilever or from the dynamic (resonance) characteristic of the beam. Based on a new stress concentration technique, which utilizes silicon beams and wires embedded in the cantilever, the force sensitivity of the cantilever is increased up to 8 fold with only about a 15% decrease in the cantilever stiffness. Moreover, the developed stress-concentrating cantilevers show almost the same resonance characteristic as conventional cantilevers. The focus of the second part of the present work is to provide guidelines for designing rectangular silicon cantilever beams to achieve maximum quality factors for the fundamental and higher flexural resonance at atmospheric pressure. The applied methodology is based on experimental data acquisition of resonance characteristics of silicon cantilevers, combined with modification of analytical damping models to match the measurement data. To this end, rectangular silicon cantilever beams with thicknesses of 5, 7, 8, 11 and 17 um and lengths and widths ranging from 70 to 1050 um and 80 to 230 um, respectively, have been fabricated and tested. To better describe the experimental data, modified models for air damping have been developed. Moreover, to better understand the damping mechanisms in a resonant cantilever system, analytical models have been developed to describe the cantilever effective mass in any flexural resonance mode. To be able to extract reliable Q-factor data for low signal-to-noise ratios, a new iterative curve fitting technique is developed and implemented. To address the challenge of frequency drift in (mass-sensitive) resonant sensors, and especially cantilever-based devices, the last part of the research deals with a novel compensation technique to cancel the unwanted environmental effects (e.g., temperature and humidity). This technique is based on exploring the resonance frequency difference of two flexural modes. Experimental data show improvements in temperature and humidity coefficients of frequency from -19.5 to 0.2 ppm/˚C and from 0.7 to -0.03 ppm/%RH, respectively. The last part of the work also aims on techniques to enhance or suppress the flexural vibration amplitude in desired overtones.

This thesis presents how experimental results, from wave power research performed offshore at the Lysekil research site, were obtained. The data were used to verify theoretical models as well as evaluate the feasibility of wave power as a future sustainable energy source. The first experiments carried out at the research site was the measurement of the force in a line where one end was connected to a buoy with a diameter of 3 m and the other end to a set of springs with limited stroke length. The system is exposed to high peak forces compared to average forces. The maximum measured force in the line, when the buoy motion is limited by a stiff stopper rope is ten times the average force in that particular sea state. The experiment performed on the first wave energy converter tested at the Lysekil Research Site is described. The infrastructure of the site is presented where the central connection point is the measuring station. The key finding is that it is possible to transform the motions of ocean waves into electrical energy and distribute it to land. Many wave energy converters must be interconnected if large amounts of energy are to be harvested from the waves. The first submerged substation intended for aggregation of energy from wave power converters is described, with focus on the measurement and control system placed inside the substation. During this experiment period the generators were equipped with many different sensors; these measurements are explained in the thesis. The system that aggregates power from the studied wave energy converter is regularly exposed to peak power of up to 20 times the maximum average output from the converter. Vertical and horizontal movement of the buoy has been measured in different ways. The result is that the vertical displacement of the buoy can be measured with a simple accelerometer circuit but it is much more complicated to measure the horizontal displacement. A special method for measuring the horizontal displacement has been implemented by measuring the strain in the enclosure and the force in the line. / Den här avhandlingen berättar om hur experimenten vid Lysekils forskningsområde för vågkraft har utförts. Insamlade mätdata har använts för att verifiera teoretiska samband som modulerats vid Elektricitetslära, Uppsala universitet. De teoretiska och praktiska resultaten har visat på att vågkraft har förutsättningarna att implementeras som en hållbar framtida energikälla. Intressanta mätmetoder har utvecklas och påfrestningarna  på utrustningin och dess samband med medel effekten har studerats. / Lysekils projektet

A adaptação passiva e estabilidade têm se tornado os dois pré-requisitos de maior importância na escolha dos materiais e técnicas de confecção em prótese implantossuportada. A proposta deste trabalho foi avaliar, com auxílio dos strain gauges ou extensômetros lineares elétricos, a deformação média ocorrida nos intermediários e na região peri-implantar mediante a instalação da infraestrutura parafusada durante sete etapas de confecção da prótese parcial fixa. Para a investigação, foi utilizado um modelo experimental homogêneo à base de poliuretano com dois implantes hexágono externo paralelos entre si. Sobre os implantes foram acoplados pilares Multi-unit de 5 mm de altura que receberam na sua superfície três strain gauges dispostos de maneira eqüidistante entre si. Também foram colados na superfície superior do bloco experimental quatro strain gauges para cada implante, posicionados nas faces mesial, distal, vestibular e lingual visando medir as tensões nestas áreas. Os testes foram realizados parafusando os corpos de prova sobre os intermediários utilizando-se para isto um dispositivo eletrônico de torque com força máxima de 10 Ncm. As leituras foram realizadas em sete momentos, obtendo os valores médios de deformação no poliuretano e no intermediário respectivamente: 1) cilindros de cobalto-cromo pré-fabricados usinados como grupo controle (36,4µε e 87,5µε), 2) infraestrutura sobrefundida em monobloco com liga de níquel-cobalto-cromo (340,3µε e 131,4µε), 3) em seguida seccionada com espaço livre para solda (43,2µε e 66,6µε), 4) seccionada com espaço para solda preenchida com resina acrílica quimicamente ativada (Duralay) (74µε e 86,8µε), 5) seccionada e soldada (280µε e 146,2µε), 6) soldada com aplicação de cerâmica (288,7µε e 151,1µε) e 7) finalizada com aplicação do glaze, acabamento e polimento (359,9µε e 197,8µε). Estes resultados mostraram um aumento crescente da deformação média tanto nos intermediários como no poliuretano durante todas as etapas de confecção, com excessão da fundição em monobloco que atingiu altos valores, próximos da prótese finalizada. Desta forma, o procedimento de soldagem diminuiu os níveis de derformação, enquanto a aplicação da cobertura cerâmica, glaze, acabamento e polimento, aumentaram as deformações. / Passive fit and stability have become the most important prerequisites during the choice of materials and techniques to implant-supported prostheses. Therefore, the aim of this study was to verify the mean deformation in abutments and simulated bone tissue around dental implants, with the use of strain gages, during framework screw retention, analyzing seven fabrication stages of the fixed partial denture. For this research, an experimental model based on homogeneous polyurethane with two external hexagon implants parallel to each other, provided with 5 mm height multi-unit abutments. For each, abutment surface received three equidistant strain gauges and the experimental block received upper surface four strain gauges, positioned on the mesial, distal, buccal and lingual aspects. The tests were performed screwing the specimens on the abutment using an electronic torque with 10 Ncm maximum force. The readings were made in seven moments, with abutment and polyurethane mean deformation, respectively: 1) control group: cobalt-chromium prefabricated machined cylinder (36,4µε e 87,5µε), 2) framework fabricated by 1-piece method in nickel-cobalt-chromium alloy (340,3µε e 131,4µε), 3) framework sectioned with space for welding (43,2µε e 66,6µε), 4) weld space filled with chemically activated acrylic resin (Duralay) (74µε e 86,8µε), 5) framework sectioned and soldered (280µε e 146,2µε), 6) framework welded and ceramic application (288,7µε e 151,1µε) and 7) framework concluded applying glaze, finishing and polishing (359,9µε e 197,8µε). The results showed the mean strain increase in abutment and polyurethane over fabrication stages, except that framework fabricated by 1-piece method reached high values close to finished prostheses. Thus, the welding procedure decreased strain levels in simulated bone tissue around dental implants, while ceramic and glaze application, finishing and polishing procedures, increased strain.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / The presence of bone loss is related to changes in the biomechanical behavior of endodontically treated teeth. The purpose of this study was to evaluate the effect of alveolar bone loss, ferrule presence and post type on the biomechanical behavior of endodontically treated maxillary canines restored with all-ceramic crowns. For the experimental analysis, forty upper human canines were selected and divided into 8 experimental groups according 3 treatment variations: bone support, without or with 5.0 mm of bone loss; ferrule presence, with or without 2.0mm of ferrule; and post type, restored with cast post and cores or glass fiber post. The restored canines were loaded at a 15- degree angle, and the deformation was measured using strain gauges placed on the buccal and proximal root surfaces. Strain results were analyzed by 3- way-ANOVA and Tukey HSD tests (α=.05). For the finite element analysis, eight 3-D models were created, following the same variations of the experimental analysis. The models were analyzed using the maximum principal stress criteria for stress distribution analysis. The presence of ferrule decreased significantly the buccal and proximal strain. The type of post showed slightly influence on the stress distribution. The presence of bone loss increased significantly the stress concentration and strain values in both regions mainly on root dentin and surrounding cortical bone. Can be possible to conclude that the presence of a ferrule improved the mechanical behavior, irrespective of the type of post. The 5.0mm of bone loss increased significantly the stress concentration and the strain on the root dentin. / A perda de inserção óssea está relacionada a mudanças no comportamento biomecânico de dentes tratados endodonticamente. O objetivo deste estudo foi avaliar o efeito da perda óssea alveolar, da presença de remanescente coronário e do tipo de retentor intra-radicular no comportamento biomecânico de caninos tratados endodonticamente e restaurados com cora em cerâmica pura. Para a análise experimental, quarenta caninos superiores foram selecionados e divididos em 8 grupos experimentais (n=10), de acordo com três fatores em estudo: suporte ósseo, ausência e presença de 5.0mm de perda óssea; remanescente coronário, ausência e presença de 2.0mm de remanescente coronário; e tipo de retentor, núcleo moldado e fundido e pino de fibra de vidro. Os caninos foram restaurados com cora em cerâmica pura reforçada por disilicato de lítio. As amostras foram submetidas ao carregamento de compressão a 15º em relação ao longo eixo do dente, e a deformação mensurada por extensômetros fixados nas superfícies radiculares vestibular e proximal. Os valores de deformação foram submetidos a Análise de variância fatorial 2X2X2 seguido pelo teste Tukey HSD (α=0,05). Para a análise de elementos finitos, oito modelos foram criados, simulando as mesmas variáveis da análise experimental. Todas as estruturas foram consideradas homogêneas e isotrópicas, a exceção do pino de fibra de vidro, considerado ortotrópico. Foi utilizado o critério de máxima tensão principal para análise de distribuição de tensões. A presença do remanescente coronário diminuiu significativamente a deformação vestibular e proximal. O tipo de pino mostrou pequena influência na distribuição de tensões. A presença da perda óssea aumentou significativamente a concentração de tensões, principalmente na dentina radicular e no osso cortical, e os valores de deformação em ambas as regiões mensuradas. Pode-se concluir que a presença de remanescente coronário dentinário melhorou o comportamento biomecânico, independente do tipo de pino. A presença da perda óssea alveolar de 5.0mm aumentou significativamente os valores de deformação e a concentração de tensões na dentina radicular. / Mestre em Odontologia

Conselho Nacional de Desenvolvimento Científico e Tecnológico / In root filled teeth, the lake of knowledge about potential deleterious of temperature rise and amount of strain generated during endodontic treatment and posterior rehabilitation with different types of intra-radicular posts is common. The produced heat and strain is dissipated on dentin structure, periodontal ligament and alveolar bone. The aim of this in vitro study was to investigate the effects of endodontic treatment and different post systems rehabilitation on the strain and temperature rise in two different root dentin regions. For this experimental investigation, twenty one extracted human canines teeth were sectioned 17 mm from their apex and divided into three groups (n = 7): cast post-and-core, fiber glass post and prefabricated steel post. All teeth were prepared for strain-gage and temperature rise measurement, attaching two strain gages on distal and two thermocouples on mesial root surfaces 2 mm and 10 mm from the crown cervical region. The samples were fixed in a specific apparatus developed for this study and strain and temperature rise were recorded during the following procedures: (1) root canal preparation, (2) Final rinse and drying, (3) obturation process, (4) canal relief, (5) post-space preparation, (6) Post modeling, (7) post trying, and (8) Resin cement curing process (9) Resin cement light curing process. Data were analyzed by oneway to compare both study factors among different procedures and two-way analysis of variance to compare post systems and root region, followed by the Tukey s HSD test ( = 0.05). Obturation process resulted in significantly higher strain values on cervical root region and the post-space preparation on the apical root region. The temperature rise reached in post-space preparation procedure was the most dangerous alteration (4.0 14.9°C), exceeding the critical values (10°C) even with water irrigation. The apical deformation produced in post-space preparation was the highest of the entire rehabilitation process: 473.9, 438.1 and 313.0 μS for fiber glass post, cast post and core and prefabricated steel post respectively. The resin cement light-curing resulted in significantly higher temperature on cervical region for all groups. Within the limitations of this study the following conclusions could be drawn: most evaluated procedures produced low temperature rise and strain values on cervical and apical root surface region, except obturation process, canal relief, post-space preparation and resin cement light-curing phase. Prefabricated steel post, inserted actively, resulted in high strain during the post trying and post cementation. Post-space preparation is a critical procedure and cautions must be taken to improve damage to the surrounding tissues. / Em dentes desvitalizados, há frequentemente falta de preocupação dos profissionais em relação ao potencial deletério da transmissão de calor e deformação na dentina, ligamento periodontal e osso alveolar gerado pela terapia endodôntica e reabilitação com retentores intra-radiculares. O objetivo deste estudo in vitro foi investigar de forma progressiva a deformação e a variação de temperatura geradas durante a realização do tratamento endodôntico e reabilitação com diferentes tipos de retentores intra-radiculares. Para esta análise experimental, vinte e um caninos superiores foram selecionados e divididos em 3 grupos experimentais (n = 7), de acordo com os três tipos de retentores em estudo: PFV, pré-fabricado reforçado com fibra de vidro; NMF, Núcleo metálico fundido em liga de NiCr; MET, retentor pré-fabricado metálico rosqueável. Todos os dentes foram seccionados de modo que permanecesse um remanescente radicular de 17,0 mm de comprimento. As amostras sofreram determinado preparo para permitir a fixação de 2 extensômetros na superfície distal e 2 termopares tipo J na superfície mesial da raiz em 2 regiões distintas: 2,0 mm (região cervical) e 10,0 mm (região apical) abaixo do limite cervical. As amostras foram fixadas em aparato desenhado especificamente para este estudo, possibilitando a mensuração, em tempo real, da deformação e da variação da temperatura durante os seguintes procedimentos: (1) Instrumentação; (2) Irrigação final e secagem; (3) Obturação; (4) Alívio imediato; (5) Preparo do espaço para retentor; (6) Moldagem para NMF; (7) Prova dos retentores; (8) Cimentação adesiva; (9) Fotoativação do cimento. Os valores de deformação foram primeiramente submetidos à Análise de variância fatorial 2-way ANOVA (3X2) seguido pelo teste Tukey HSD (=0,05) e novamente submetidos à Análise de variância fatorial One-Way ANOVA seguido pelo teste Tukey HSD (=0,05). A obturação do canal radicular resultou em valores significativamente altos de deformação na região cervical e o preparo do espaço para retentor na região apical. O intervalo da variação de temperatura alcançada durante o preparo do espaço para retentor foi à alteração mais alarmante (4,0 14,9°C), acima do nível crítico (10°C), mesmo na presença de constante irrigação. A deformação apical produzida nesta mesma etapa foi a maior em todo o processo de reabilitação avaliado: 473,9; 438,1; e 313,0 μS para os grupos PFV, NMF e MET respectivamente. A fotoativação resultou em variação de temperatura na região apical em todos os grupos experimentais, porém seus valores foram abaixo do nível crítico. Pode-se concluir que a maioria dos procedimentos avaliados apresentaram valores baixos de aumento de temperatura e deformação em ambas as regiões cervical e apical, exceto a obturação, o alívio imediato, o preparo do espaço para retentor e a fotoativação do cimento resinoso. O pino metálico pré-fabricado resultou em maiores valores de deformação durante as etapas de prova e cimentação do retentor. O preparo do espaço para retentor constitui etapa crítica e precauções devem ser tomadas para evitar danos mecânicos e biológicos ao dente e as estruturas de suporte adjacentes. / Mestre em Odontologia

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / The widening of the root canal increases its fracture risk and is not clear yet, the influence of the materials and techniques used to restore these teeth. The aim of this study was to evaluate the effect of different posts and restorative techniques in the fracture resistance, fracture mode and root strain in canals excessively widened. One hundred thirty five standardized bovine roots, with similar dimensions and endodontically treated, were randomly divided in 9 groups (n=15) with the root canals prepared with 10 mm depth and 1.5 mm diameter. All roots received ferrule in the coronal ending with 0.5 mm depth and 2 mm extension. The roots of two reference groups were reconstructed with nickel-chromium metallic cast post-and-core (NMF) and glass fiber post (PFV) with composite resin core. For the experimental groups (weakened roots - wc groups), the root canals were over prepared additionally with the depth of 9 mm and the diameter increased to approximately 3,5 mm. Then the roots were restored with metallic cast post-and-core (wcNMF); glass fiber post (wcPFV); glass fiber post associated with accessory glass - ap - fiber post (wcPFVap); direct composite resin - cr - in the medial and cervical thirds after luting the post (wcPFVcr); direct composite resin associated with accessory posts in the medial and cervical thirds, after luting the post (wcPFVcrap); the post was reembased indirectly with composite resin - icr - (wcPFVicr); the post was reembased indirectly with composite resin associated with accessory posts (wcPFVicrap). All posts were fixed with chemical resinous cement, the core was made with composite resin and the roots restored with metallic crown. The samples were submitted to 3x105 mechanical fatigue cycles of 50 N load and fracture resistance measured in a mechanical testing machine with tangential load application (135º). Five samples of each group received two strain gauges adhered in the mesial and buccal surfaces of the root, 1mm below the cervical crown ending, in the center of the tooth, to measure roots strain under continuous 0 to 100 N loading. Fracture mode was classified in accordance to the degree of destruction of the dental structure, in catastrophic or repairable. The data were submitted to ANOVA (2x2)l to one-way and Tukey´s test (α=0.05). The factorial analysis demonstrated significant decrease of the fracture resistance and catastrophic failures for the wcNMF group. Roots widened canals restored with composite resin and/or accessory fiber posts result in fracture resistance values similar to NMF group, however, these demonstrated more repairable fracture. The strain-gauge analysis didn t present significant differences in the superficial strain of the root. Fiber glass post associated with composite resin or with accessory fiber glass posts, seems to be more indicated as alternative to metallic cast post-and-core in weakened roots, because of the lower risk of catastrophic fractures. / O alargamento do canal aumenta o risco de fratura dentária e ainda não está clara a influência dos materiais e técnicas empregados para restaurar dentes com estas características. Assim, o objetivo deste estudo foi avaliar o efeito de diferentes pinos e técnicas restauradoras na resistência à fratura, padrão de fratura e deformação de raízes com canais excessivamente alargados. Foram empregadas 135 raízes bovinas com dimensões semelhantes, tratadas endodonticamente, aleatoriamente divididas em 9 grupos (n= 15). Os canais foram preparados com 10 mm de profundidade e 1,5 mm de diâmetro e as raízes receberam preparo com férula de 0,5 mm de profundidade e 2 mm de extensão. Dois grupos de referência foram restaurados com retentores intraradiculares metálicos fundidos em níquel-cromo (NMF) e pino de fibra de vidro (PFV) com núcleo de preenchimento em resina composta. Para os demais grupos, os canais radiculares foram alargados na profundidade de 9 mm e o diâmetro aumentado para ±3,5 mm, padronizando a espessura de dentina remanescente em 0,5mm no terço coronário da raiz. Os canais alargados (ca) foram então restaurados com, núcleo metálico fundido (caNMF); pino de fibra de vidro (caPFV); pino de fibra de vidro associado a pinos de fibra de vidro acessórios (caPFVpa); preenchimento direto com resina composta nos terços médio e cervical após cimentação do pino (caPFVrd); preenchimento direto com resina composta associado a pinos acessórios, após cimentação do pino (caPFVrdpa); pino reembasado com resina composta de forma indireta (caPFVri); pino reembasado com resina composta de forma indireta associado a pinos acessórios (caPFVripa). Todos os procedimentos de cimentação foram realizados com cimento resinoso de ativação química, os núcleos de preenchimento em resina composta e as raízes restauradas com coroa total metálica. As amostras foram submetidas a 3x105 ciclos de fadiga mecânica de 50N de carga. Em cinco amostras de cada grupo, dois extensômetros foram aderidos à raiz, um na mesial e outro na vestibular, 1 mm abaixo do limite cervical da coroa, no centro do dente, para mensurar a deformação das raízes sob carregamento contínuo de 0 a 100N. A resistência à fratura (N) das amostras foi então medida em máquina de ensaio mecânico com aplicação de carga tangencial (135º). Os dados foram submetidos à análise de variância fatorial (2x2), para comparar o efeito do tipo de retentor em função do tipo de raiz, e em fator único, para avaliar os métodos de preenchimento, seguido pelo teste de Tukey (α=0,05). O padrão de fratura foi classificado de acordo com o grau de comprometimento da estrutura dentária em catastrófica ou reparável. A análise estatística fatorial demonstrou significativa redução da resistência à fratura e falhas catastróficas para o grupo caNMF. Valores de resistência comparável ao grupo NMF e padrão de fratura reparável foram obtidos em raízes com canais alargados, sempre que a resina composta ou pinos de fibra acessórios foram utilizados. Não houve diferença significante na deformação externa da raiz entre os grupos estudados. Pode-se concluir que o uso de pinos de fibra de vidro, associado ao preenchimento com resina composta e/ou pinos de fibra de vidro acessórios, parece ser mais indicado como alternativa ao núcleo metálico fundido em raízes fragilizadas, devido ao menor risco de fraturas catastróficas. / Mestre em Odontologia