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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.

Purpose: To evaluate the microtensile bond strength (µTBS) to dentin of 4 adhesive systems, the micromorphology of the adhesive/dentin interface and to compare the results to the µTS (cohesive strength) of sound dentin and resin composite. Occlusal surfaces of 24 extracted caries-free human molars were cut flat to expose the dentin surface. They were randomly assigned to 4 groups (n = 6): Adper Scotchbond Multi Purpose Plus (MP), Adper Single Bond (SB), Clearfil Protect Bond (CP) and Adper Prompt (AP). Adhesive systems were applied and "crowns" were built using Z100. Other 5 human molars were sectioned to obtain square-shaped dentin blocks and 5 resin blocks were built using a composite resin, Z100. After storage in distilled water at 37 °C for 24 h, stick-shaped specimens were obtained for all groups (n = 5) with 0.8 mm 2 and subjected to µTBS or µTS test. Results were analyzed using One-Way ANOVA and Tukey's test at p < 0.05. The remaining bonded teeth were cut in two halves perpendicularly to the bonded interface and prepared for SEM analyses. No significant differences were found among CP (45.6 + 7.4 MPa), SB (43.3 + 6.5 MPa) and MP (35.1 + 5.9 MPa) (p > 0.05). The lowest result was found for AP (27.4 + 4.7 MPa), although not statistically different from MP. Most specimens (89.4%) showed predominant adhesive failure. None of the systems tested reached the µTS values of dentin (108.5 + 9.4 MPa) and Z100 (86.5 + 3.6 MPa). Bonded interfaces showed lower µTBS than those µTS of dentin and resin composite blocks. The all-in-one self-etching adhesive had the lowest µTBS.

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