В данной работе были рассмотрены различные испытательные машины, изучен принцип и особенности работы разрывной машины для статических испытаний металлов Р-10. Проведены расчеты геометрических параметров гидроцилиндров (основного рабочего и захватов), прочностной и расчет на устойчивость. Также, исходя из перечисленных расчетов подобран рабочий насос и среда – масло. Смоделированы детали модели в пакете программ SolidWorks, а в пакете MATLAB Simscape составлена сборка разрывной машины и добавлена система с гидроприводом. В результате исследования была получена имитационная модель статической разрывной машины для металлов, при помощи которой было проведено моделирование испытания на растяжение. Для этого был выбран образец стали известной марки с заранее определенными геометрическими параметрами. После чего к образцу были приложены различные усилия, и сняты показания удлинения образца. На основе этого был получен график. Затем с помощью данных усилие/перемещение и начальных геометрических параметров были рассчитаны пределы пропорциональности, текучести, прочности на основании которых и был определен материал образца. Данный пример демонстрирует правильность разработки подобных моделей в системе MATLAB, которые могут позволить провести детальные исследования процессов работы механизмов машины во время испытаний, в том числе оценить характеристики гидравлической системы разрывной испытательной машины. / In this dissertation, various testing machines were considered, the principle and features of the operation of a tensile testing machine for static testing of metals R-10 were studied. Calculations of the geometrical parameters of hydraulic cylinders (main working and grippers), strength and stability calculations were carried out. Also, based on the above calculations, a working pump and a medium - oil were selected. The details of the model were modeled in SolidWorks, and the tensile testing machine assembly was assembled in MATLAB Simscape and the hydraulic actuator system was added. As a result of the study, a simulation model of a static tensile testing machine for metals was obtained, with the help of which a simulation of a tensile test was carried out. For this, a sample of well-known brand steel with predetermined geometric parameters was selected. After that, various forces were applied to the sample, and indications of the elongation of the sample were taken. Based on this, a graph was obtained. Then, using the force / displacement data and the initial geometric parameters, the limits of proportionality, yield, strength were calculated, on the basis of which the sample material was determined. This example demonstrates the correctness of developing such models in MATLAB. They can make it possible to conduct detailed studies of the operation of the machine mechanisms during testing, including the evaluation of the characteristics of the hydraulic system of the tensile testing machine.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Research in concrete has advanced to such an extent that it is now possible to add steel fibres to concrete in order to improve its durability and ductility. This led to a research group in Europe, FIB, who has provided guidelines to designing Steel Fibre Reinforced Concrete (SFRC) structures. They have found that it is possible for SFRC beams in flexure to be in static equilibrium. However, the time-dependent behaviour of SFRC has not been researched fully and it requires further investigation. When looking at a concrete beam in flexure there are two main stress zones, the compression zone and the tension zone, of which the tensile zone will be of great interest. This study will report on the investigation of the tensile time-dependent behaviour of SFRC in order to determine how it differs from conventional concrete. The concrete has been designed specifically to exhibit strain-softening behaviour so that the material properties of SFRC could be investigated fully. Factors such as shrinkage and tensile creep of SFRC were of the greatest importance and an experimental test setup was designed in order to test the tensile creep of concrete in a simple and effective manner. Comparisons were be made between the tensile creep behaviour of conventional concrete and SFRC where emphasis was placed on the difference between SFRC specimens before and after cracking occurred in order to determine the influence of steel fibre pull-out. The addition of steel fibres significantly reduced the shrinkage and tensile creep of concrete when un-cracked. It was however found that the displacement of fibre pull-out completely overshadowed the tensile creep displacements of SFRC. It was necessary to investigate what effect this would have on the deflection of SFRC beams in flexure once cracked. Viscoelastic behaviour using Maxwell chains were used to model the behaviour of the tensile creep as found during the tests and the parameters of these models were used for further analyses. Finite Element Analyses were done on SFRC beams in flexure in order simulate creep behaviour of up to 30 years in order to determine the difference in deflections at mid-span between un-cracked and pre-cracked beams. The analyses done showed that the deflections of the pre-cracked SFRC beams surpassed the requirements of the Serviceability Limit States, which should be taken into account when designing SFRC beams. / AFRIKAANSE OPSOMMING: Die navorsing in beton het gevorder tot so ‘n mate dat dit nou al moontlik is om staal vesels by die beton te voeg sodat dit beton se duursaamheid en duktiliteit te verbeter. Dit het gelei tot ‘n groep in Europa, FIB, wat dit moontlik gemaak het om Staal Vesel Beton (SVB) strukture te ontwerp. Hulle het gevind dat dit moontlik is vir SVB balke om in statiese ewewig te wees tydens buiging. Die tyd afhanklike gedrag van SVB is egter nog nie deeglik ondersoek nie en benodig dus verdure ondersoek. Wanneer ‘n balk in buiging aanskou word kan twee hoof spanningzones identifiseer word, ‘n druk zone en ‘n trek zone, waarvan die trek zone van die grootste belang is. Hierdie studie gaan verslag lewer oor die ondersoek van tyd-afhanklike trekgedrag van SVB om te bepaal hoe dit verskil van konvensionele beton. Die beton was spesifiek ontwerp om vervormingsversagtende gedrag te wat maak dat die materiaal eienskappe van SVB ten volle ondersoek kan word. Faktore soos krimp en die trekkruip van SVB was van die grootste belang en ‘n eksperimentele toets opstelling was ontwerp om die trekkruip van beton op ‘n eenvoudige en effektiewe manier te toets. Daar was vergelykings getref tussen die trekkruip gedrag van konvensionele beton en SVP en groot klem was geplaas op die verskil tussen SVB monsters voor en na die monsters gekraak het om te bepaal wat die invloed was van staalvesels wat uittrek. Die byvoeging van staalvesels het beduidend die kruip en trekkruip van beton verminder. Daar was alhoewel gevind dat die verplasing van die uittrek van staalvesels heeltemal die trekkruip verplasings van SVB oorskadu het. Dit was nodig om te sien watse effek dit op die verplasing van SVB balke in buiging sal hê. Viskoelastiese gedrag deur Maxwell kettings was gebruik om die gedrag van trekkruip, soos gevind deur die toetse, te modelleer en die parameters van hierdie modelle was verder gebruik vir analises. Eindige Element Analises was gedoen op SVB balke in buiging om die trekkruip gedrag tot op 30 jaar te simuleer op die verskil tussen die defleksies by midspan tussen ongekraakte en vooraf gekraakte balke te vind. Die analises het gewys dat die defleksies van die vooraf gekraakte balke nie voldoen het aan die vereistes van die Diensbaarheid limiete nie, wat in ag geneem moet word wanneer SVB balke ontwerp word.

Simulations are powerful and important tools for gaining insight into powder processes. Ultimately, simulations have the potential to replace experiments. Thus, accurate models and insight into the essential factors for descriptions of powder behaviour are required. In this thesis, discrete element method (DEM) simulations of granule flow and compression were evaluated to deduce parameters and potential models essential for the experimental and numerical correspondence. In addition, the evolution in tablet microstructure during compression was studied using mercury porosimetry. Granule flow was measured using angle of repose, discharge rate, and shear. The granular flow depended primarily on particle shape and surface texture due to the mutual influence of these two parameters on the inter-particle forces. Rolling friction stabilised both the heap formation and promoted shear in the elastic quasi-static flow regime. Thus, rolling friction was established to be an essential simulation parameter for the correspondence to experiments. Current compression models often neglect the elastic compact deformation during particle loading. In this thesis, two fundamentally different models were evaluated with focus of including the elastic deformation. The first model comprised a maximal particle overlap, where elastic deformation commences. The second model accounted for the contact dependence and impingement at high relative densities. This model was based on a truncated-sphere followed by a Voronoi extension. The validity of the models was demonstrated by the elastic qualitative correspondence to experimental compressions for ductile materials. In tablets, the void (inter-granular pore) diameter was dependent on the degree of compression. Thus, the degree of compression provides an indication of the tablet microstructure. The microstructure was subsequently observed to be related to the tablet tensile strength as inferred from a percolation threshold required for formation of coherent tablets. In summary, this thesis has shed light onto the potential of simulating flow and compression of granulated pharmaceutical powders using DEM. Continuous work in the area are required to further improve the models to increase the experimental and numerical correspondence.

AbstractAN IN-VITRO COMPARISON OF THE RETENTION OF PREFABRICATED PARALLEL-SIDED VENTED TITANIUM POSTS CEMENTED WITH THREE DIFFERENT DUAL-POLYMERIZABLE RESIN CEMENTSBy Maha M. El-Sayed, B.D.S., D.M.D.A Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science at Virginia Commonwealth University.Virginia Commonwealth University, 2003Thesis Director: David R. Burns, D.M.D. Associate Professor and Program DirectorGraduate ProsthodonticsDepartment of ProsthodonticsPurpose: The purpose of this in-vitro study was to compare the retentive strength of an autopolymerizing resin cement to three dual-polymerizable resin cements when used to cement paraposts without light activation and to relate diametral tensile stress and hardness as a measure of the degree of polymerization to the retentive strength of the different dual-polymerizable resin cements. Material and methods: 60 human extracted premolar teeth were endodontically-treated and randomly divided into 4 test groups (n=15). Parapost XP posts (size 5) were cemented using Panavia 21(control), Panavia F, RelyX Unicem and Linkmax resin cements. The latter three cements were dual-polymerizable and were not light-activated, and the control cement was autopolymerizable. Also, 140 resin cement samples were fabricated for diametral tensile stress and Knoop hardness testing. Each test had 70 samples, 10 of each of the following groups: Panavia 21, Panavia F light-activated, Panavia F autopolymerized, RelyX Unicem light-activated, RelyX Unicem autopolymerized, Linkmax light-activated, Linkmax autopolymerized. Post retention, diametral tensile stress and surface hardness tests were performed 1 week after sample fabrication or post cementation.Results: ANOVA and Tukey-Kramer statistical analysis revealed significant differences among the test groups for the three tests. Conclusions: Within the limitations of this in vitro study, tested dual-polymerization resin cements had similar or superior parapost retention to the control autopolymerizing resin cement without photoactivation. Dual-polymerizable resin cements had improved diametral tensile stress and surface hardness when light-activated than when autopolymerized. No correlation was observed between surface hardness and diametral tensile stress or between the tested physical properties of the resin cements and their retentive qualities

This study is an initial attempt to investigate the possibility of substituting conventional laboratory destructive testing techniques at Sandvik's strip steel production facilities with the 3MA (Micro-magnetic Multi-parameter Microstructure and Stress Analysis) NDT (nondestructive testing) technique. The interest for the research comes from various problems with the actual destructive testing method. Sandvik manufactures thin strip steel (among other products) and controls the quality of its product by taking samples from the ends of the strip and measuring the sample's material properties in a separate laboratory. Hence, the sample preparation process is time and material consuming, and the results obtained from the laboratory measurements are not always representative of the real values along the whole length of the strip (usually several kilometers). Therefore, the present project involves the correlation between three material properties (Vickers hardness, tensile strength and carbide density) and a selection of micro-magnetic parameters measured with the 3MA-II equipment manufactured by the Fraunhofer IZFP institute. The 3MA-II system is based on four measuring techniques (harmonic analysis, magnetic Barkhausen noise, incremental permeability and Eddy current testing) and is capable of recording up to 41 micro-magnetic parameters. Samples of two different steel grades (composition) were used in the study. The results for hardness and tensile strength (average relative errors of 1.04% and 0.78%, respectively) corroborated the applicability of the 3MA technique to steel strip inspection. Thus, the implementation of this technique would lead to an improvement in the company's energy efficiency and sustainability. However, finding a good correlation between micromagnetic parameters and material properties is not always possible and, in the case of carbide density, no reliable correlation was achieved. So, further experiments are proposed for future studies regarding carbide density and other material properties.

Ce travail porte sur l'étude de liens entre les propriétés mécaniques de comprimés modèles composés de billes de verre et les caractéristiques physico-chimiques des liants, constitués de sucres et préparés sous forme de sirops. Le procédé de fabrication consiste en une méthode modifiée de compression humide. Deux paramètres de formulation ont été testés : le taux de saturation en sirop et sa concentration massique. Nous en avons tiré une variable unique qui est la fraction massique de sucre ajoutée aux billes de verre. Ces paramètres se sont avérés essentiels dans la maîtrise de la tenue mécanique des comprimés. Il en est de même pour leurs conditions de stockage. Une corrélation linéaire a été établie entre une activité de l'eau, définie comme critique, du fructose, du galactose, du glucose, du lactose et du saccharose et l'apparition du phénomène de transition vitreuse pour chacun de ces sucres, engendrant une chute brutale dans la résistance mécanique de leurs comprimés respectifs. Le taux de cristallisation des sucres et l'absence d'anomérie sont aussi des paramètres qui semblent être à l'origine d'une meilleure tenue mécanique des comprimés / This work focuses on the study of relationships between the mechanical properties of model compacts composed by glass beads and the physicochemical characteristics of binders consisting of sugars and prepared in the form of syrups. Fructose, galactose, glucose, lactose and sucrose were used in this study. The manufacturing process consists in a modified wet compression method. Two formulation parameters were tested: the saturation ratio and the mass concentration of the syrup. We deduced from them a single variable which is the mass fraction of sugar added to the glass beads. These parameters were essential in controlling the mechanical strength of the compacts. It has been shown that storage conditions also influence tablets properties. A linear correlation was established between a specific water activity value, defined as critical, and the glass transition temperature for each of sugars, resulting in a collapse in mechanical strength of the compacts. The rate of crystallization of sugar and the absence of anomeric forms are also parameters that seem to be targeted in order to increase compacts mechanical strength

Cold-blooded horses find their use at present mainly in tensile work in forest stands. Motion mechanics plays the key role in estimating their potential for performing this activity. Subsequently, it is used in their selection and reproduction. In the process, applied load the horse is working with significantly influences the characteristics of a movement. Therefore, for horses doing tensile work, an objective assessment of their movement mechanics is important, not only during demonstration but also under a changing load. The aim of this study was to prepare and evaluate an experiment for assessing the quantitative characteristics of motion mechanics (step length, action height and running speed) of a cold-blooded horse with no load and with a load of different weight using videographic kinematic analysis. The data obtained were statistically processed to assess changes in step length, action height and running speed depending on the changing load. The results of our experiment showed that the step length decreases with increasing weight of the load. From an average value of 1.94 m at run without a load, it drops to an average value of 1.02 m at a maximum monitored load of 500 kg. A high dependence (r=-0.93) of the step length reduction on the tensile load was found. The dependence is strongly evincible (p<0.001). Changes in action height with increasing load weight are different for the forelimb and rear limb. The forelimb has an almost constant value (~ 0.08m) and no dependence (p=0.977) on the changing weight of the load has been demonstrated. The rear limb shows a strong correlation (p<0.001) to the increasing weight of the load. The correlation coefficient r=0.52 indicates only a slight dependence. This difference can be explained by different function and construction of the limb. The running speed derived from the horizontal marker from the tracking mark on the back is uniform in all observed cases and decreases from 1.95 m.s-1 to 1.19 m.s-1 with increasing weight of the load. The dependence is strongly evincible (p<0.001) and the correlation coefficient of r=-0.94 indicates a strong dependence. The results obtained from the horizontal head velocity component are very well matched to the spine results. The results provided by this method can be an invaluable tool in objective detection of utility and breeding potential of cold-blooded horse in tensile work. Based on these findings, we can recommend further development of videographic kinematic analysis application to objectify the evaluation of quantitative characteristics of motion mechanics for zootechnical and breeding practice.

O uso de núcleos metálicos fundidos é comum na Odontologia Restauradora para promover a substituição de estruturas perdidas em dentes tratados endodonticamente. Estes núcleos podem ser fundidos em ligas nobres ou ligas básicas: as ligas alternativas apresentam vantagens mas são susceptíveis à corrosão. O titânio foi introduzido na Odontologia com o objetivo de compensar as deficiências dos metais básicos, principalmente a corrosão e seus produtos. Então, a proposta deste estudo foi comparar a resistência à tração de núcleos metálicos fundidos confeccionados em liga de ouro tipo III, titânio e titânio tratado superficialmente com solução de Kroll quando fixados com diferentes agentes cimentantes. Quarenta e dois caninos humanos extraídos foram selecionados, a porção coronária foi removida e a raiz remanescente foi tratada endodonticamente. Todos os espécimes foram divididos em seis grupos (n=7). O espaço para pino foi preparado a uma profundidade de 10mm usando-se brocas de Largo. Os núcleos foram fundidos em liga de ouro tipo III e titânio c.p. e fixados com cimento de fosfato de zinco ou cimento resinoso (Panavia F). A resistência à tração foi determinada em uma máquina universal de ensaios a uma velocidade de 0,5mm/min utilizando-se uma célula de carga de 50 Kgf. Os resultados foram analisados estatisticamente por ANOVA, demonstrando que não houve diferença estatisticamente significante entre os grupos. Dentro das limitações deste estudo pode-se concluir que os núcleos metálicos fundidos em titânio c.p. fixados com cimento fosfato de zinco ou cimento resinoso são uma alternativa viável aos núcleos metálicos fundidos em ouro. / The use of cast post and core is common in restorative dentistry to provide long-term tooth structure replacement for endodontically treated teeth. They could be cast in precious or basic alloys: the alternative alloys present advantages but they are susceptible to corrosion and its effects. The titanium was introduced to Dentistry with the objective of compensating the metal basic deficiencies, mainly the corrosion. Then, the purpose of this study was to compare the tensile resistance among gold alloy, titanium, and titanium after a superficial treatment with Kroll’s solution when fixed with different luting agents. Forty two human extracted canines were selected, the coronal aspect of each tooth was removed and the remaining root received endodontic therapy. All specimen were divided into six groups (n=7). The post space was prepared at a depth of 10mm using a Largo’s drill. The cast post and core were manufactured using a type III gold alloy and titanium. Cast post and core were fixed with zinc phosphate or resin luting agent (Panavia F). Tensile bond strength of the specimens was measured with a universal testing machine at a crosshead speed of 0,5mm/min and cell-load of 50 Kgf. Data (Kgf) were statistically analyzed by ANOVA. The results demonstrated that there was not a significant difference among the groups. Within the limitations of this study it has been conclude that the titanium fixed with zinc phosphate or resin luting agent is a viable alternative to the gold alloy to fabricate cast post and cores.

Este estudo investigou a resistência à tração (ou limite de resistência à tração- LRT) e a porosidade de reembasadores resilientes temporários modificados por concentrações inibitórias mínimas (CIMs) de agentes antifúngicos para o biofilme Candida albicans (SC5314). Para os testes de LRT, corpos de prova em forma de halteres (n=7) com uma área transversal de 33 mm x 6 mm x 3 mm foram produzidos para os materiais resilientes (Trusoft e Softone) sem (controle) ou com incorporação de cinco fármacos em suas CIMs: nistatina- 0,032 g; diacetato de clorexidina- 0,064; cetoconazol- 0,128 g; miconazol- 0,256 g; itraconazol-0,256 g (grama de fármaco por grama de pó de material resiliente). Após a plastificação, as amostras foram imersas em água destilada a 37°C durante 24 h, 7 e 14 dias e, então, testadas em tensão em uma máquina universal de ensaios (EMIC DL-500 MF) a 40 mm/min. A porosidade foi mensurada por absorção de água, com base na exclusão do efeito plastificante. Inicialmente, determinou-se por isotermas de sorção, que a solução de armazenagem adequada para os corpos de prova (65 mm x 10 mm x 3,3 mm) de ambos os materiais foi o cloreto de cálcio anidro a 50% (S50). Assim, o fator de porosidade (FP) foi calculado para os grupos de estudo (n=10) formados por espécimes sem (controle) ou com incorporação de fármaco em suas CIMs (nistatina, clorexidina ou cetoconazol) após a armazenagem em água destilada ou S50 por 24 h, 7 e 14 dias. Os dados de resistência à tração (MPa) e percentagem de alongamento (%) foram submetidos à ANOVA de 3 fatores seguida pelo teste de Tukey (=0,05). Os dados de porosidade foram analisados estatisticamente por ANOVA de medidas repetidas para 4 fatores e teste de Tukey (=0,05). Ao final de 14 dias, a resistência à tração para ambos os materiais foi significativamente menor nos grupos modificados pelo miconazol e itraconazol em relação aos outros grupos (P<0,0001), que não mostraram diferenças significativas entre si (P>0,05). Após 7 e 14 dias em água, o miconazol e itraconazol adicionados a ambos os materiais resultaram em percentagens significativamente menores de alongamento em comparação com os outros fármacos e ao controle (P<0,0001), que foram semelhantes entre si (P>0,05). O cetoconazol não resultou em alterações significativas no FP para ambos os materiais resilientes em água ao longo de 14 dias (P>0,05). Em comparação aos controles, houve aumento dos FPs do Softone e Trusoft aos 14 dias de imersão em água somente após a adição de nistatina e clorexidina e de clorexidina, respectivamente (P<0,05). Ambos os materiais não apresentaram alterações significativas no FP em até 14 dias de imersão na S50, em comparação aos controles (P>0,05). Em todas as condições experimentais, os FPs do Softone e Trusoft foram significativamente menores quando imersos em S50 em comparação com a água destilada (P<0,05). Concluiu-se que a adição de nistatina, clorexidina e cetoconazol nas CIMs para o biofilme de C. albicans não resultou em efeitos deletérios na resistência à tração e na percentagem de alongamento dos materiais resilientes temporários para base de prótese até o período de 14 dias. A adição de antifúngicos nas CIMs não resultou em efeitos adversos à porosidade de ambos os materiais resilientes temporários em diferentes períodos de imersão em água, com exceção da clorexidina e nistatina no Softone e clorexidina no Trusoft aos 14 dias. Não foram observados efeitos deletérios para a porosidade de ambos os materiais resilientes modificados com as CIMs dos fármacos durante os 14 dias de imersão na S50. / This study investigated the tensile strength (ultimate tensile strength- UTS) and porosity of temporary soft denture liners modified by minimum inhibitory concentrations (MICs) of antifungal agents for Candida albicans biofilm (SC5314). For UTS tests, dumbbell-shaped specimens (n=7) with a central cross-sectional area of 33 mm x 6 mm x 3 mm were produced by resilient materials (Trusoft and Softone) without (control) or with incorporation of five drugs at MICs: nystatin- 0.032 g; chlorhexidine diacetate-0.064 g; ketoconazole- 0.128 g; miconazole- 0.256 g; itraconazole- 0.256 g (each per gram of soft liner powder). After plasticization, specimens were immersed in distilled water at 37°C for 24 h, 7 and 14 days, and then tested in tension in a universal testing machine (EMIC DL-500 MF) at 40 mm/min. The porosity was measured by water absorption, based on exclusion of the plasticizer effect. Initially, it was determined by sorption isotherms that the adequate storage solution for specimens (65 mm x 10 mm x 3.3 mm) of both materials was 50% anhydrous calcium chloride (S50). Then, the porosity factor (PF) was calculated for the study groups (n=10) formed by specimens without (control) or with drug incorporation at MICs (nystatin, chlorhexidine or ketoconazole) after storage in distilled water or S50 for 24 h, 7 and 14 days. Data of tensile strength (MPa) and elongation percentage (%) were submitted to 3-way ANOVA followed by Tukey\'s test (=0.05). Data of porosity were statistically analyzed by 4-way repeated measures ANOVA and Tukeys test (=0.05). At the end of 14 days, the tensile strength for both materials was significantly lower in the groups modified by miconazole and itraconazole compared to the other groups (P<0.0001), which showed no significant difference between them (P>0.05). After 7 and 14 days in water, miconazole and itraconazole added into both materials result in significant lower elongation percentages compared to the other drugs and control (P<.0001), which were similar to each other (P>0.05). Ketoconazole resulted in no significant changes in PF for both liners in water over 14 days (P>0.05). Compared to the controls, Softone and Trusoft PFs were increased at 14-day water immersion only after addition of nystatin and chlorhexidine, and chlorhexidine, respectively (P<0.05). Both materials showed no significant changes in PF in up to 14 days of S50 immersion, compared to the controls (P>0.05). In all experimental conditions, Softone and Trusoft PFs were significantly lower when immersed in S50 compared to distilled water (P<0.05). It was concluded that the addition of the nystatin, chlorhexidine and ketoconazole at MICs for C. albicans biofilm resulted in no harmful effects on the ultimate tensile strength and elongation percentage of the temporary soft denture liners up to 14-day period. The addition of antifungals at MICs resulted in no detrimental effects for the porosity of both temporary soft liners in different periods of water immersion, except for chlorhexidine and nystatin in Softone and chlorhexidine in Trusoft at 14 days. No deleterious effect was observed for the porosity of both soft liners modified by the drugs at MICs over 14 days of S50 immersion.

Interfaces adesivas flexíveis, com maior capacidade de dissipação de tensões poderiam prevenir falhas provenientes das tensões geradas durante a contração de polimerização, variações térmicas e esforços mastigatórios. Isso poderia ser obtido através do aumento da espessura da camada de adesivo. O objetivo deste trabalho foi comparar a resistência de união (RU) à dentina de dois sistemas adesivos (SA) aplicados com diferentes volumes de adesivo (uma ou duas camadas) e submetidos ou não às ciclagens térmica e mecânica (CTM). A superfície dentinária de 40 terceiros molares hígidos foi exposta com uma lixa de granulação 600. Dois sistemas adesivos foram testados: Scotchbond Multiuso (SBMU) e Clearfil SE Bond (CSEB). Seus respectivos adesivos foram aplicados através de uma micropipeta (8 ou 16µl) em uma área delimitada de 52 mm 2 e blocos de resina composta (Z250) foram construídos incrementalmente. Metade da amostra foi armazenada em água destilada por 24 h e submetida às ciclagens térmica (1.000; 5-55ºC) e mecânica (500.000 ciclos / 12 kgf). A outra metade foi apenas armazenada em água destilada por 72 h. Após isso, os dentes foram seccionados, longitudinalmente, em cortes perpendiculares entre si, a fim de se obterem corpos-de-prova em formato de paralelogramo com aproximadamente 0,8mm 2 de secção transversal. Os palitos foram submetidos ao teste de microtração a 1,0 mm/min e o modo de fratura analisado. A RU foi expressa como um índice que incluiu os valores de RU dos diferentes padrões de fratura, além dos palitos prematuramente fraturados (P). Os dados foram submetidos à análise de variância de 3 fatores. O teste de qui-quadrado foi utilizado (p<0,05) para verificar diferenças na freqüência de P. Dois fatores foram significantes: “SA" e “CTM". SBMU e grupos não-ciclados apresentaram maior RU do que CSEB e grupos ciclados respectivamente. Uma maior freqüência de P foi observada para os grupos ciclados. Uma camada adicional de adesivo não influenciou na RU de interfaces feitas com SBMU ou CSEB, enquanto a CTM levou à redução da RU das interfaces. / Dentin bonding interfaces with increased capacity of stress dissipation are able to prevent failures due to polymerization contraction, thermal and mechanical stresses. This would be obtained by increasing adhesive layer thickness. The purpose of this study was to compare the resin-dentin microtensile bond strengths (BS) of two adhesive systems (AS) applied with different volumes of adhesive resin (one and two coats) submitted or not to thermal and mechanical loading (TML). A flat superficial dentin surface was exposed on 40 third molars with a 600-grit SiC paper. Two systems were tested: Scotchbond Multipurpose (SBMP) and Clearfil SE Bond (CSEB). After primer application, the adhesive layer was applied by a micropipette (8 or 16µl) to a delimited area (52mm 2 ) and resin blocks (Z250) were built incrementally. Half of the sample was stored in distilled water for 24h and then submitted to thermal (1,000; 5-55ºC) and mechanical cycles (500,000; 12kgf). The other half was stored in distilled water (72h). Teeth were then sectioned to obtain sticks (0.8 mm 2 ) to be tested under tensile mode (1.0mm/min). The fracture mode was analyzed at 400X. BS was expressed as an index that included the BS values of different fracture patterns and the prematurely debonded specimens (D). The data was analyzed by three-way ANOVA. The &#967; 2 test was used (p<0.05) to compare the frequency of D specimens. The main factors AS and TML were significant. SBMP and non-cycled groups showed higher BS to dentin. A higher frequency of D was observed for the cycled groups. The application of an adhesive layer in two coats for a three-step etch&rinse and a two-step self-etch systems, to act as an intermediate flexible layer, was not able to minimize the damage caused by thermal and mechanical load in a low C-factor cavity.