No description available.

No description available.

No description available.

No description available.

Objective: To compare the adhesive strength in dentin of three universal adhesive systems in vitro by means of the shear test. Materials and methods: Seventy-five bovine teeth were selected and cut. Dentin was exposed from the buccal surface of the crowns with 220 grit sandpaper, and samples were then inserted in transparent acrylic bases (15x10mm). The samples were randomly divided in 3 groups (n=25): G1-Universal adhesive system Scotchbond™ Universal (3M ESPE-USA); G2-Universal adhesive system Peak Universal Bond (Ultradent); G3-Universal adhesive system Tetric N-Bond (Ivoclar Vivadent). The adhesive procedures were carried out according to the instructions of each manufacturer and the restorative procedures were carried out with micro-cylinders (made of Tygon type tubing 0.79x1.5mm) of the composite resin Filtek™ Z350XT-A2 (3M ESPE-USA). The samples were incubated at 37ºC (+/-5ºC) for 24 hours. Adhesive strength was evaluated in a universal test machine by means of the shear test (0.5mm/ min, 500N) and the resulting fracture type was evaluated with a Dinolite digital microscope (x200). The results were analyzed by descriptive statistics (Mean±SD), and inferential statistics by a one-way ANOVA. Results: No statistically significant differences were found between the universal adhesive systems evaluated G1 (14.91±4.76), G2 (16.90±4.11) and G3 (17.34±4.04)/(p=0.114). Conclusions: The shear test resulted in similar values of immediate adhesive strength of the three universal adhesive systems used. / Revisión por pares

Adesivos sensíveis à pressão (PSA do inglês - Pressure Sensitive Adhesives) são produtos que aderem a superfícies imediatamente após a aplicação de pequenas pressões. Têm grandes vantagens sobre outros tipos de adesivos, principalmente por necessitarem apenas de uma aplicação inicial de pressão para apresentar o efeito permanente de adesão. Neste trabalho foram avaliadas três composições distintas de PSA, sendo uma delas considerada como referência, e duas condições diferentes de processamento, com o objetivo principal de obter um adesivo com alta resistência ao cisalhamento e boa aderência. Todas as amostras foram produzidas em laboratório utilizando um moinho de dois rolos e um misturador do tipo sigma. Essas composições foram baseadas em borrachas com insaturações, que permitem a formação de ligações cruzadas, tornando o adesivo mais resistente. As alterações impostas na composição (adição de óxido metálico e resinato) e a mudança na condição de processamento (nível de reação para formação de ligações cruzadas) levaram a diferentes propriedades dos adesivos obtidos; como valores de adesão, grau de ligação cruzada, resistência a cisalhamento e peso molecular. Os resultados encontrados neste trabalho mostram que a adição de 5pcr de óxido de zinco aumenta em até 64% a resistência ao cisalhamento em relação à amostra de referência, enquanto que 5 pcr de resinato de zinco causa um incremento de aproximadamente 21%. Também foi possível observar que o alto nível de reação (60 minutos) confere uma quantidade de ligações cruzadas pelo menos duas vezes maior que a obtido para o baixo nível de reação (30 minutos) / Pressure Sensitive Adhesives (PSA) are materials which bond to adherent surfaces at room temperature immediately as low pressure is applied. This kind of material has a number of advantages of adhesives bonding, especially because they need low pressure to effect permanent adhesion to an adherent. In this work three different PSA formulations were tested under two process condition. The final product obtained can be used over flexible web, as poly (vinyl chloride) tapes. Samples were prepared trough a two-roll mill and sigma mixer in a laboratory production scale. The composition was based on rubber material that has double molecular chain, which allows cross-linking, making the adhesive more resistant. Small changing on formulation (adding5phrofmetallic oxide or zinc resinate) and process condition (reaction level) took to different results as cross-link degree, adhesion properties, shear resistance and molecular weight. The results showed that adding small amount of metallic oxide can increase up to 64% of shear resistance and adding zinc resinate compound can increase about 21%. And also is possible to conclude that high reaction level (60 minutes) takes to at least double cross-linking degree compared with low reaction level (30 minutes)

published_or_final_version / Paediatric Dentistry / Master / Master of Dental Surgery

This thesis details the work carried out under two research projects at the University of Surrey. The first project titled The Design of Structural Adhesive Joints', was of three years duration from September 1985 to August 1988 and was sponsored by the Science and Engineering Research Council. The second project, sponsored by Ford UK Ltd, and tided 'A General Joint Analysis Facility extended certain aspects of the analysis work initiated In the first period of research. The objective of the work was to address the problem of integrating structural adhesives Into the design process and to provide procedures that would facilitate this integration in a quantitative, rather than the more usual qualitative way. To be effective, such an approach needed to consider not only a means of analyzing a proposed joint but also a way of predicting the actual failure of that joint. An extensive literature survey of analyses available to the design engineer has been completed. The analyses investigated were found to be lacking in several critical respects, and as part of this research, methods of analysis overcoming some of these limitations have been developed. The analyses produced are based on earlier approaches but extended and modified as appropriate. The work on all the analyses produced has been carried out by considering a simple adherend-adhesive sandwich configuration. Five different analyses, considering the sandwich to be modelled with differing degrees of complexity, have been produced. In all of the analyses the adherends are assumed to behave as cylindrically bent plates capable of sustaining both tensile and shear forces and bending moments, with the adhesive transmitting both tensile and/or shear loads. Initially an elastic solution was obtained, adopting a relatively simple approach. This enabled the subsequent enhancement of including non-linear material behaviour to utilize the same governing equations, thus maintaining consistentcy. The General Elastic Analysis (GEA) has been extensively simplified to produce a number of two parameter design formulae suitable for use by an engineer at an early stage in the design process. The two analyses produced by this simplification are called the Simplified Peel Analysis (SPA) and the Simplified Shear Analysis (SSA), so called because they consider the named component of stress in the adhesive layer only. The GEA was then extended to include non-linear material properties in the adhesive layer, and an analysis called the Non-linear Adhesive Analysis (NLAA) was produced. A programme of validation using the NLAA and a non-linear finite element analysis of similar joint configurations was carried out. Additional comparisons with existing analyses have also been undertaken where possible. The NLAA has been shown to produce extremely accurate results for the stresses in the adhesive layer when compared with the component stresses predicted by the finite element method (FEM). The NLAA has been used successfully to determine the spread of yield in a single-lap joint, giving dose agreement with results from analysis using the FEM, but with much reduced computer and operator time. The final stage of the work was concerned with the Inclusion of non-linear adherend material properties, and an analysis called the Full Non-linear Analysis (FNLA) has been produced which Incorporates this refinement to the general model. Again the finite element method has been used to assess the accuracy of this new analysis, and the results from this work are presented here. Derivations of both forms of the elastic analysis and of the non-linear and full non-linear analyses are reported in Chapters 4 and 5 and the software appropriate to each Is described fully. The Initial survey of available literature has shown that there Is considerable lack of knowledge about possible causes of joint failure. Specifically, It Is noted that a criterion by which joint failure can be measured has not been uniquely defined. In an attempt to provide a criterion or criteria to enable the prediction of joint failure a 'Failure Criteria' test and analysis programme has been completed. Joint configurations were manufactured using a range of adhesives with different levels of ductility, and adherends of different stiffnesses. Batches of these test coupons were tested to failure under both predominantly mode I and mode 11ty pes of loading. Both FEM and FNLA analyses of each test configuration have been carried out, and the stress and strain distributions at the levels of failure load were established for each batch and studied to establish any correlation between various proposed failure criteria. Close agreement between certain factors and the equivalent bulk material properties was noted for test batches. The applicability of various failure criteria for both the mode I and mode II test configurations and possible general criteria are discussed. The failure of the mode I test configurations has been shown to be governed by the local level of maximum principal stress at the end of the overlap. The mode II test configurations also show dose agreement in terms of the maximum principal stress, but agreement with bulk data Is poor. Therefore, a further failure criterion is proposed for the mode II joints in terms of the 'global yielding' of the adhesive layer. The bulk property testing of the adherend and adhesive materials to establish their physical properties for use in the finite element analysis of the test programme Is also fully documented.

No description available.

No description available.