The definition of an optimal elastic modulus for a post is controversial. This work hypothesized that the influence of the posts' elastic modulus on dentin stress concentration is dependent on the load direction. The objective was to evaluate, using finite element analysis, the maximum principal stress (sigma(max)) on the root, using posts with different elastic modulus submitted to different loading directions. Nine 3D models were built, representing the dentin root, gutta-percha, a conical post and the cortical bone. The softwares used were: MSC.PATRAN2005r2 (preprocessing) and MSC.Marc2005r2 (processing). Load of 100 N was applied, varying the directions (0 degrees, 45 degrees and 90 degrees) in relation to the post's long axis. The magnitude and direction of the sigma(max) were recorded. At the 45 degrees and 90 degrees loading, the highest values of sigma(max) were recorded for the lowest modulus posts, on the cervical region, with a direction that suggests debonding of the post. For the 0 degrees loading, the highest values of sigma(max) were recorded for higher modulus posts, on the apical region, and the circumferential direction suggests vertical root fracture. The hypothesis was accepted: the effect of the elastic modulus on the magnitude and direction of the sigma(max) generated on the root was dependent on the loading direction.

Finite element analysis (FEA) utilizing models with different levels of complexity are found in the literature to study the tendency to vertical root fracture caused by post intrusion ("wedge effect"). The objective of this investigation was to verify if some simplifications used in bi-dimensional FEA models are acceptable regarding the analysis of stresses caused by wedge effect. Three plane strain (PS) and two axisymmetric (Axi) models were studied. One PS model represented the apical third of the root entirely in dentin (PS-nG). The other models included gutta-percha in the apical third, and differed regarding dentin-post relationship: bonded (PS-B and Axi-B) or nonbonded (PS-nB and Axi-nB). Mesh discretization and material properties were similar for all cases. Maximum principal stress (sigma max) was analyzed as a response to a 165 N longitudinal load. Stress magnitude and orientation varied widely (PS-nG: 10.3 MPa; PS-B: 0.8 MPa; PS-nB: 10.4 MPa; Axi-B: 0.2 MPa; Axi-nB: 10.8 MPa). Axi-nB was the only model where all sigma max vectors at the apical third were perpendicular to the model plane. Therefore, it is adequate to demonstrate the tendency to vertical root fractures caused by wedge effect. Axi-B showed only part of the sigma max perpendicular to the model plane while PS models showed sigma max on the model plane. In these models, sigma max)orientation did not represent a situation where vertical root fracture would occur due to wedge effect. Adhesion between post and dentin significantly reduced sigma max.

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A durabilidade das restaurações diretas está intimamente relacionada ao vedamento do ângulo cavossuperficial de preparos cavitários. Apesar de toda a evolução pela qual os sistemas adesivos e materiais restauradores têm passado, ainda não há perfeito selamento da interface dente-restauração. Logo, há necessidade de aprimorar as técnicas e os materiais restauradores e adesivos, com o objetivo principal de minimizar a formação de fendas marginais e consequente microinfiltração. Analisando a literatura sobre o tema, observa-se que existem diferentes metodologias para a realização do ensaio de microinfiltração. O objetivo deste trabalho é apresentar possíveis fatores que podem interferir nos resultados dese teste. Para tal fim, foi realizada uma revisão bibliográfica detalhada do tema. Conclui-se que a metodologia mais frequentemente encontrada na literatura utiliza dentes humanos com preparos cavitários de Classe V, como método de envelhecimento a ciclagem térmica, o corante azul de metileno e a leitura dos resultados feita através da análise qualitativa. Descritores: Infiltração dentária • Metodologia. ABSTRACTThe durability of direct restorations is closely related to the superficial angle of dental cavities. Despite all the changes which the adhesive systems and restorative materials have passed, the sealing of the tooth / restoration interface is not perfect yet. Therefore, the improvement of the techniques and restorative materials is important to minimize the formation of marginal gaps and consequent microleakage. Reviewing the literature on this subject, it was noted that there are different methodologies for conducting the microleakage test. The objective of this study is to discuss possible factors that may affect results of this test. It was concluded that the methodology most commonly found in the literature uses human teeth with cavity preparations of Class V; the thermal cycling; the methylene blue dye; and the qualitative analysis to avaliate the results. Descriptors: Dental Leakage • Methodology.

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<p><strong>Objective: </strong>Early carious lesions in bovine and humanenamel developed in vitro using a pH cycling regimenwere compared. <strong>Material and Methods: </strong>Fifteencentral bovine incisors and fifteen recently extractedhuman third molars were randomly divided into twogroups: ten for the cross-sectional microhardness test(MT) and five for polarized light microscopy (PLM)analysis. Enamel blocks measuring 5 x 5 mm weremade from the buccal face of the teeth. The blocksused for the MT were sliced into two halves: “A” and“B”. “A” slices were embedded in acrylic resin, withthe face of the dentin-enamel junction left exposedfor the MT prior to pH cycling. “B” slices and wholeblocks were coated with acid-resistant varnish,except a 3 x 3 mm central window, and submitted tothe pH cycling regimen (demineralizing solution for3 h and remineralizing solution for 21 h) over fiveconsecutive days. The “B” slices were then submittedto the MT and the whole blocks were processed forthe PLM study. <strong>Results: </strong>The PLM analysis revealedshallow, extensive lesions in the bovine enamel,hardly showing the superficial, dark and translucentzones, as well as deep cavity lesions in the humanenamel, with the body of the lesion and the darkzone evident. The MT revealed a significant decreasein microhardness in the superficial levels of thebovine enamel caries and at all depth levels of thehuman enamel caries. <strong>Conclusion: </strong>The pH cyclingregimen adopted led to the development of deeperand more demineralized carious lesions in humanenamel than bovine enamel</p><p>Keywords<br />Dental caries; Dental enamel; Microhardness tests; Polarization microscopy.</p>