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Objectives This study aimed at comparing the stress distribution in shear and micro-shear test set-ups using finite element analysis, and suggesting some parameter standardization that might have important influence on the results. Methods Two-dimensional plane strain finite element analysis was performed using MSCPatran® and MSCMarc® softwares. Model configurations were based on published experimental shear and micro-shear test set-ups and material properties were assumed to be isotropic, homogeneous and linear-elastic. Typical values of elastic modulus and Poisson's ratios were assigned to composite, dentin and adhesive. Loading conditions considered a single-node concentrated load at different distances from the dentin-adhesive interface, and proportional geometry (1:5 scale, but fixed adhesive layer thickness in 50 μm) with similar calculated nominal strength. The maximum tensile and shear stresses, and stress distribution along dentin-adhesive interfacial nodes were analyzed. Results Stress distribution was always non-uniform and greatly differed between shear and micro-shear models. A pronounced stress concentration was observed at the interfacial edges due to the geometric change: stress values farther exceeded the nominal strength and tensile stresses were much higher than shear stresses. For micro-shear test, the relatively thicker adhesive layer and use of low modulus composites may lead to relevant stress intensification. An appropriate loading distance was established for each test (1 mm for shear and 0.1 mm for micro-shear) in which stress concentration would be minimal, and should be standardized for experimental assays. Significance The elastic modulus of bonded composites, relative adhesive layer thickness and load application distance are important parameters to be standardized, once they influence stress concentration.

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 (σmax) 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 σmax 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 σmax perpendicular to the model plane while PS models showed σmax on the model plane. In these models, σmax orientation did not represent a situation where vertical root fracture would occur due to wedge effect. Adhesion between post and dentin significantly reduced σmax. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008

Os objetivos deste estudo foram comparar, através de análise de elementos finitos, a distribuição de tensões em modelos que representam arranjos experimentais nor-malmente utilizados em testes de cisalhamento e micro-cisalhamento, verificar a tendência de variar o local de início e o modo de fratura em função de mudanças nos parâmetros dos ensaios e analisar a influência de dois modos de fixação do substrato sobre a concentração de tensões. Os modelos bidimensionais em estado plano de deformações representaram o compósito (híbrido ou flow) aderido à dentina através de uma camada de adesivo de 50 μm. Duas condições de fixação da dentina foram estabelecidas: na primeira (mais rígida), os deslocamentos foram restritos em todas as direções nos nós das arestas que representam as três superfícies livres de adesão e na segunda, a restrição foi colocada apenas na parte posterior da dentina. Foi aplicado um carregamento pontual a várias distâncias da interface dentina-adesivo, de modo a obter um tensão nominal constante de 4MPa. Foram analisadas as tensões máximas de tração e cisalhamento, a distribuição das tensões ao longo dos nós da interface dentina-adesivo e os vetores de tensão máxima principal, como indicativos do local de início e o provável modo de fratura. A distribuição de tensões ao longo da interface aderida foi sempre não uniforme e apresentou picos muito ele-vados em todos os casos, o que conduz a pensar que os valores de resistência nominal não são representativos da máxima tensão suportada no momento da fratura. A tensão de tração predominou sobre a de cisalhamento. O módulo de elasticidade do compósito aderido, a espessura relativa da camada de adesivo e a distância de aplicação da carga influenciam a concentração de tensões e devem ser padroniza-dos. Para o teste de micro-cisalhamento, a camada de adesivo relativamente mais espessa e o uso do compósito com baixo módulo de elasticidade propiciaram a in-tensificação das tensões. O ensaio de cisalhamento parece mais suscetível que o de micro-cisalhamento para que o início da ruptura ocorra no substrato, pois o ponto de maior concentração de tensões localizou-se na dentina em alguns casos e verifica-se pequena diferença de módulo entre os maiores vetores localizados no adesivo e na dentina de base. O teste de micro-cisalhamento, embora mais favorável a que as fraturas se iniciem no adesivo, concentra muito a tensão, especialmente com a utili-zação de resinas do tipo flow, o que o torna menos representativo da máxima tensão que o espécime realmente resistiu no momento da fratura. The objectives of this study were to compare the stress distribution in finite element models that represented experimental designs commonly used for shear and micro-shear bond strength testing, to verify the tendency to vary the location and mode of fracture as a consequence of changes in the studied parameters, and to analyze the influence of two substrate restriction conditions on stress concentration. Bi-dimensional plane strain models represented a composite (hybrid or flow) bonded to dentin through a 50 μm adhesive layer. Two dentin restriction conditions were estab-lished: in the first (more rigid), movements were restricted in all directions on the nodes located in the dentin surface edges free of adhesion, and in the second, re-striction was imposed only to the posterior dentin surface. Concentrated loading was applied at several distances from the dentin-adhesive interface so as to obtain con-stant nominal bond strength of 4MPa. Maximum tensile and shear stress values, stress distribution along the dentin-adhesive interfacial nodes and the principal maximum stress vectors as indicative of the most probable location and mode of frac-ture were analyzed. Stress distribution along bonded interfaces was always non-uniform and presented very high stress peaks for all cases. This led to the assump-tion that nominal bond strength values are non-representative of the maximum stress supported at fracture. Tensile stresses were always predominant over shear stresses. The composite elastic modulus, relative adhesive layer thickness and different load application distances influenced stress concentration and should be stan-dardized. For micro-shear tests, the relatively thicker adhesive layer and use of a low modulus composite propitiated stress intensification. The shear test seems to be more susceptible than micro-shear to fracture initiation in the substrate, once the point of highest stress concentration was in some cases located in dentin, and small modulus difference was verified between the greatest stress vectors located both on the adhesive and dentin base. Although more favorable to fracture initiation in the adhesive, the micro-shear test design highly concentrated stresses, especially when flow composite was modeled, hence it might be less representative of the maximum stress the specimen resisted at fracture.

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 mm² 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.

To analyze the influence of two placement techniques and two adhesive systems on the marginal microleakage of Class II resin-based composite restorations using different resin composite materials.Two hundred standardized Class II cavities (5 mm x 3 mm x 1.5 mm) were cut in human premolars and restored using five resin composite materials (A.L.E.R.T.-AL, Solitaire-SO, SureFil-SU, Filtek A110-A, and Z100-Z), two adhesive systems (Bond 1-B1 and EtchPrime 3.0-EP), and two placement techniques (incremental or bulk). Specimens were thermocycled (700 cycles, 5 degrees - 55 degrees C, 1 min dwell time), immersed in 0.5% methylene blue solution for 4 h, and sectioned longitudinally to evaluate the extent of microleakage. Data were submitted to statistical analysis using the Kruskal-Wallis test.It was observed that both adhesive systems presented similar results (p0.05), and neither achieved complete marginal sealing. The bulk placement technique led to greater microleakage than the incremental technique (p0.001). Restorations prepared using SO resin composite showed greater microleakage than those performed using Z or AL materials. However, SO obtained similar values of microleakage when compared to SU and A materials.The use of incremental placement technique resulted in less microleakage for Class II resin-based composite restorations. No difference was observed among adhesive systems regarding prevention of marginal dye penetration. Furthermore, the type of resin composite material employed for restoration may have an influence on the extent of microleakage.

To evaluate the bond strength of a self-etching (Clearfil SE Bond) and a single-bottle (Excite) adhesive system using two cavity configurations (C-factors 5 and 1).Class I cavities (3 x 4 x 2.5 mm) were prepared in 28 extracted human molars using diamond burs under water cooling. Teeth were divided into 4 groups: G1: Excite, C-factor 5; G2: Excite, C-factor 1; G3: Clearfil, C-factor 5; G4: Clearfil, C-factor 1. To determine C-factor 5, systems were applied to all cavity walls according to the manufacturers' instructions (5 bonded, 1 unbonded). For C-factor 1, lateral walls were isolated using nail varnish, and adhesive systems were only applied to the pulpal floor (5 unbonded, 1 bonded). Cavities were restored using Tetric Ceram composite resin (Ivoclar/Vivadent), and bulk light cured for 40 s (500 mW/cm2). Teeth were stored in distilled water for 24 h at 37 degrees C, and then sectioned using a diamond disk, yielding stick-shaped specimens with a bonded area of approximately 0.8 mm2. Specimens were submitted to the microtensile bond test at a rate of 1 mm/min speed in a universal testing machine.Resin-dentin bond strengths (MPa) were submitted to ANOVA and Tukey's tests (p0.05) [number of specimens]: G1 = 35.8b [43]; G2 = 48.9a [55]; G3 = 45.9a [60]; G4 = 49.0a [53]. There was no statistically significant difference between adhesive systems for C-factor 1. For C-factor 5, Clearfil SE Bond produced higher values when compared to the other group.Changes in C-factor only affected the total-etch adhesive system tested. This may be a result of the different filler volume in the self-etching system, and not of the bonding technique itself.

The difficulty with comparing data obtained from different research centers calls for the standardization of laboratory procedures. This in vitro study compared the shear bond strength (SBS) of two adhesive systems--a self-etching system, EtchPrime 3.0 and a one-bottle total-etch system, Single Bond--using two methods of load application (orthodontic edge wire loop and knife-edge blade). The hypothesis of substrate influence on the results obtained for both tests was also investigated. Twenty-four recently extracted human teeth were embedded in PVC tubes using acrylic resin and divided into two groups (n=12). A proximal surface of each tooth was wet-ground flat to expose dentin. EtchPrime 3.0 and Single Bond adhesive systems were applied according to the manufacturers' instructions, and cone-shaped restorations were then built using Z100 resin composite. After storage in distilled water at 37 degrees C for 24 hours, the specimens were submitted to SBS testing using an orthodontic edge wire loop. The same teeth were again embedded in PVC tubes using acrylic resin and the other proximal surface was wet-ground flat to expose dentin. The specimens were prepared as explained above, and after storage in distilled water under the same previous conditions, they were submitted to SBS testing using a knife-edge blade. Two-way ANOVA and Tukey's tests were performed to determine any statistically significant differences among testing conditions. Results indicated that SBS values obtained for EtchPrime 3.0 were significantly lower than Single Bond for both methods of load application (p0.001). Regarding the load application method, statistically significant higher values (p0.01) were obtained for EtchPrime 3.0 when the knife-edge blade was used, whereas, no significant difference was observed between the two methods for Single Bond. There was a significant correlation between the bond strength values obtained on the same tooth (p0.05). SEM examination found that EtchPrime 3.0 demonstrated narrower tags than Single Bond. Moreover, the peritubular dentin was not adequately decalcified when EtchPrime 3.0 was used.

To analyze the influence of two placement techniques on Knoop and Vickers hardness of class II cavities restored using packable (A.L.E.R.T., Solitaire 2, SureFil) and conventional microfilled and hybrid (Filtek A110 and Z250, respectively) resin composites.Fifty standardized class II cavities (5 x 3 x 1.5 mm3) were prepared in human premolars. They were divided into ten groups (n = 5) and restored according to each resin composite material (A.L.E.R.T., Solitaire 2, SureFil, Filtek A110 and Z250) and placement technique (incremental or bulk). After storage in distilled water at 37 degrees C for 24 h, they were thermal cycled (700 cycles/5-55 degrees C, 1 min dwell time) and sectioned longitudinally. One section from each specimen was embedded and polished for Knoop and Vickers hardness measurements. Sixteen indentations were performed for each restoration, eight on the occlusal and eight on the cervical surfaces.Results were submitted to ANOVA and demonstrated that all materials presented lower hardness values at the cervical surfaces when the bulk placement technique was employed, when compared to the occlusal surfaces (p0.001) whereas the same did not occur with the incremental technique. Pearson's correlation test demonstrated a positive correlation between Vickers and Knoop hardness numbers.The use of bulk placement technique resulted in lower values of hardness at the cervical surfaces of class II restorations. Values obtained using Knoop hardness test showed a high correlation with Vickers hardness measurements.

To evaluate microleakage at the dentin margins of Class II resin-based composite restorations using four simplified adhesive systems: EtchPrime 3.0, PrimeBond NT, Clearfil Liner Bond 2V and Clearfil SE Bond, upon thermal and mechanical stresses.Forty slot preparations (5mm x 3mm x 1.5mm) were cut in sound human molars with gingival margins below the cement/enamel junction. All adhesive systems were applied strictly according to manufacturers' instructions. Cavities were restored using Clearfil AP-X composite resin. After finishing and polishing, teeth were submitted to thermal (x700, 5-55 degrees C, 60-second dwell time) and consecutively mechanical cycling (100,000 cycle; 8 Kgf load). Specimens were coated with nail polish, immersed in silver nitrate for 2 hours and sectioned longitudinally with a diamond disc. The extent of leakage was ranked using a 0-4 scale.Statistical analysis was performed using Kruskal-Wallis test. Minimal leakage occurred with Clearfil SE Bond. There was a statistically significant difference (P0.01) between this system and Clearfil Liner Bond 2V, although the latter also showed low values of dye penetration. No statistically significant difference was found between EtchPrime 3.0 and PrimeBond NT. Both showed statistically greater leakage than the two other systems (P0.01).

O objetivo deste estudo foi comparar à resistência à fratura de três técnicas de colagem usadas para restaurar dentes fraturados hígidos e com tratamento endodôntico associado ou não a colocação de pino de fibra de vidro. Noventa incisivos humanos foram aleatoriamente divididos em três grupos de 30 dentes cada. No grupo A, os dentes não foram tratados endodonticamente, enquanto os dentes dos grupos B e C foram submetidos ao tratamento endodôntico, seguido de restauração da câmara pulpar com resina composta. Todos os dentes foram fraturados por uma carga axial aplicada na superfície vestibular para obter fragmentos dentais. Os dentes de cada grupo foram novamente subdivididos em três subgrupos: colagem simples [CS], chanfro vestibular [CV] e chanfro circunferencial [CC]). Antes da colagem dos fragmentos, pinos de fibra de vidro foram colocados nos dentes do grupo C. Todos os fragmentos dos dentes (grupos A, B e C) foram colados utilizando um cimento de dupla ativação (Duo- Link, Bisco Inc). No grupo CS, nenhum preparo adicional foi realizado após colagem, porém no restante dos dentes realizou-se uma canaleta vestibular (grupo CV) ou uma canaleta circunferencial ao redor da linha de colagem (CC) com aproximadamente 1,0 mm de profundidade. As canaletas foram restauradas com resina composta microhíbrida. Por fim, os espécimes foram submetidos a mesma carga axial no mesmo ponto pré-determinado. A resistência à fratura após o procedimento restaurador foi expressa em porcentagem de resistência do dente íntegro. Os dados foram submetidos a uma análise de variância de dois fatores (Grupo vs. Técnica de colagem) e teste de Tukey (?=0,05). Somente o fator principal Técnica de colagem foi estatisticamente significante (p0,05) entre si e superior ao alcançado pela técnica de colagem simples (p0.05) fracture strength recovery, which was superior to the bonded only technique (p