Este trabalho avaliou in vitro a resistência à microtração de resinas compostas de baixa contração de polimerização em superfície dentinária após a degradação da interface adesiva. A amostra do experimento foi composta de 78 terceiros molares, sendo que 60 dentes foram divididos aleatoriamente em 6 grupos (n = 10) para o ensaio de microtração e 18 dentes adicionais (três dentes por grupo) foram utilizados para a análise da interface adesiva por meio da microscopia eletrônica de varredura (MEV). As variáveis de resposta quantitativas foram a resistência adesiva por meio do ensaio de microtração (Megapascal) e a classificação e cálculo dos valores percentuais dos tipos de fratura por meio de MEV. A análise estatística demonstrou que nos grupos NTC, o grupo Z250 apresentou diferença estatisticamente significante com os demais grupos K e P90, sendo estes semelhantes entre si. Após a realização da termociclagem observou diminuição nos valores de resistência nos grupos estudados, sendo que o grupo Z250 apresentou diferença estatisticamente significante em comparação ao grupo K e P90, que foram semelhantes entre si. A qualidade da interface adesiva por meio de MEV após o teste de microtração demonstrou que fraturas mistas foram prevalentes em todos os grupos avaliados. Em relação a interface adesiva, quando o sistema adesivo Clearfill SE Bond foi utilizado, pôde-se observar uma camada de adesivo espessa, camada híbrida e tags. No entanto, para o sistema adesivo P90, não foi possível observar camada híbrida, tags e foram observadas fendas interfaciais tanto às 24 horas como após envelhecimento. / This in vitro study evaluated the microtensile bond strength of polymerization of lowshrinkage composite resins in dentin surface after degradation of the adhesive interface. The sample of the study was composed by 78 third molars, 60 teeth were randomly divided into 6 groups (n = 10) for the microtensile testing and 18 additional teeth (three teeth per group) were used for the analysis of adhesive interface by means of scanning electron microscopy (SEM).The quantitative response variables were bond strengths to dentin through the microtensile test (Megapascal) and the classification and calculation of percentage values of theta peso fracture by SEM. Statistical analysis showed that the groups NTC, the Z250 group showed a statistically significant difference with others groups K and P90, which are similar to each other. After the performance of thermo cycling was observed decline in strength values of the studied groups, with the Z250 group showed a statistically significant difference when compared to the K group and P90, which were similar. The analysis showed the presence of mixed and adhesive fractures. Regarding the adhesive interface could be observed in P90 (NTC) and P90 (TC), presence cracks and gaps interfacial group. In the other groups was observed thick and dense layer Clearfill SE Bond and presence of tags into the tubules. Thus, it was concluded that the low polymerization shrinkage resins present lower average microtensile bond strength values both after 24 hours and after aging procedures of the adhesive interface. The quality of the adhesive interface by SEM after the microtensile test showed that mixed fractures were prevalent in groups Z250 (NTC), Z250 (TC), K (NTC), K (TC), P90 (NTC).And adhesive fracture was prevalent in the P90 group (CT).In relation the adhesive interface, when the adhesive system Clearfill SE Bond was used, it was noted a layer of thick adhesive, hybrid layer and tags. However, for the adhesive system P90, it was not possible to observe the hybrid layer, tags and interfacial cracks were observed both after 24 hours and after aging.

Este trabalho avaliou in vitro a resistência à microtração de resinas compostas de baixa contração de polimerização em superfície dentinária após a degradação da interface adesiva. A amostra do experimento foi composta de 78 terceiros molares, sendo que 60 dentes foram divididos aleatoriamente em 6 grupos (n = 10) para o ensaio de microtração e 18 dentes adicionais (três dentes por grupo) foram utilizados para a análise da interface adesiva por meio da microscopia eletrônica de varredura (MEV). As variáveis de resposta quantitativas foram a resistência adesiva por meio do ensaio de microtração (Megapascal) e a classificação e cálculo dos valores percentuais dos tipos de fratura por meio de MEV. A análise estatística demonstrou que nos grupos NTC, o grupo Z250 apresentou diferença estatisticamente significante com os demais grupos K e P90, sendo estes semelhantes entre si. Após a realização da termociclagem observou diminuição nos valores de resistência nos grupos estudados, sendo que o grupo Z250 apresentou diferença estatisticamente significante em comparação ao grupo K e P90, que foram semelhantes entre si. A qualidade da interface adesiva por meio de MEV após o teste de microtração demonstrou que fraturas mistas foram prevalentes em todos os grupos avaliados. Em relação a interface adesiva, quando o sistema adesivo Clearfill SE Bond foi utilizado, pôde-se observar uma camada de adesivo espessa, camada híbrida e tags. No entanto, para o sistema adesivo P90, não foi possível observar camada híbrida, tags e foram observadas fendas interfaciais tanto às 24 horas como após envelhecimento. / This in vitro study evaluated the microtensile bond strength of polymerization of lowshrinkage composite resins in dentin surface after degradation of the adhesive interface. The sample of the study was composed by 78 third molars, 60 teeth were randomly divided into 6 groups (n = 10) for the microtensile testing and 18 additional teeth (three teeth per group) were used for the analysis of adhesive interface by means of scanning electron microscopy (SEM).The quantitative response variables were bond strengths to dentin through the microtensile test (Megapascal) and the classification and calculation of percentage values of theta peso fracture by SEM. Statistical analysis showed that the groups NTC, the Z250 group showed a statistically significant difference with others groups K and P90, which are similar to each other. After the performance of thermo cycling was observed decline in strength values of the studied groups, with the Z250 group showed a statistically significant difference when compared to the K group and P90, which were similar. The analysis showed the presence of mixed and adhesive fractures. Regarding the adhesive interface could be observed in P90 (NTC) and P90 (TC), presence cracks and gaps interfacial group. In the other groups was observed thick and dense layer Clearfill SE Bond and presence of tags into the tubules. Thus, it was concluded that the low polymerization shrinkage resins present lower average microtensile bond strength values both after 24 hours and after aging procedures of the adhesive interface. The quality of the adhesive interface by SEM after the microtensile test showed that mixed fractures were prevalent in groups Z250 (NTC), Z250 (TC), K (NTC), K (TC), P90 (NTC).And adhesive fracture was prevalent in the P90 group (CT).In relation the adhesive interface, when the adhesive system Clearfill SE Bond was used, it was noted a layer of thick adhesive, hybrid layer and tags. However, for the adhesive system P90, it was not possible to observe the hybrid layer, tags and interfacial cracks were observed both after 24 hours and after aging.

Dans le cadre des applications transports, et plus particulièrement de "l’avion plus électrique", avec une demande toujours plus présente de réduction d’encombrement et de poids, la tendance est à l’intégration de plus en plus poussée des convertisseurs statiques. L’augmentation de leur densité de puissance et celle des contraintes thermiques, induites par l’environnement dans lequel ces structures sont localisées, deviennent de plus en plus critiques. La gestion thermique de ces dispositifs est assurée par des systèmes de refroidissement sur lesquels sont montés les composants semi-conducteurs via un matériau d’interface thermique. Une gestion performante sera obtenue par la diminution de la résistance thermique globale entre les éléments dissipatifs et le milieu ambiant grâce en autre à l’amélioration du système de refroidissement et des propriétés thermiques des matériaux constituant le module. Or cette interface est un point délicat du transfert de chaleur car elle peut représenter plusieurs dizaines de pourcents de la résistance thermique globale. Elle nécessite donc une connaissance approfondie de son comportement aux sollicitations thermiques. Après un état de l’art sur les matériaux d’interfaces thermiques et les méthodes de caractérisation des propriétés thermophysiques des matériaux, nous proposons la mise en œuvre d’outils expérimentaux et mathématiques permettant de suivre l’éventuelle évolution de matériaux d’interfaces utilisés en électronique de puissance au cours d’un vieillissement par cyclage en température. Pour cela, deux méthodes sont présentées. La première repose sur la mesure de la résistance thermique des interfaces en régime stationnaire avec un transfert de chaleur monodimensionnel alors que la seconde, basée sur une caractérisation transitoire thermique d’un système, permet d’en identifier les constantes de temps et le réseau Résistance-Capacité du système testé. Des travaux de simulations numériques ont été menés sur les deux types de bancs expérimentaux, d’un côté pour pouvoir évaluer les pertes thermiques latérales du banc statiques, de l’autre côté pour montrer qu’il est bien possible de détecter une variation de la résistance thermique d’un matériau d’interface par l’analyse de l’impédance thermique. / In the context of transportation applications, and especially the "more electric aircraft", with an ever present demand for space and weight reduction, the trend is to integrate more extensive of static converters. The increase in power density and the thermal stresses induced by the environment in which these structures are located, are becoming increasingly critical. Thermal management of these devices is provided by cooling systems on which are mounted the semiconductor components via a thermal interface material. Effective management will be achieved by reducing the overall thermal resistance between the dissipative elements and the environment by improving the cooling system and thermal properties of the materials constituting the module. However, this interface is a delicate point of heat transfer because it can represent several tens of percent of the circuit total thermal resistance. It therefore requires a thorough knowledge of their behavior in thermal stresses. After a state of the art on the thermal interface materials and methods for characterizing thermophysical properties of materials, we propose the implementation of experimental and mathematical tools to monitor any change of interface materials used in power electronics during aging by temperature cycling. For this, two methods are presented. The first is based on the measurement of the thermal resistance of the interfaces with a steady one-dimensional heat transfer, while the second, based on a characterization of a transient thermal system, allows to identify the time constants and the resistor and capacitor network of the tested system. Numerical simulations were carried out on two types of experimental benches, on one side in order to assess the lateral heat losses from static bench, on the other side to show that it is possible to detect a change in the thermal resistance of a TIM with the analysis of the thermal impedance.