[36] and [37] used finite-element stress analyses to demonstrate

[36] and [37] used finite-element stress analyses to demonstrate that tensile and shear bond-strength

measurements were highly dependent on the geometry of the test apparatus, the nature of the load application, the presence or absence of adhesive flash and the materials involved. The authors reported that non-uniform stresses acted upon the bonded interface; they therefore questioned the concept of ‘average stress’ for measurements of bond strength. The greatest emphasis has been placed on measuring tensile bond strengths (at right angles to the tooth/adhesive interface). All of the forces acting on an adhesive bond in vivo can be resolved as components acting at right angles and parallel to the interface www.selleckchem.com/products/PD-0325901.html (shear). It is therefore important to measure the shear strength in order to evaluate a bond adequately. Bond strength-testing jigs have been designed such that the maximum stress in the shear apparatus is transmitted along the interface, whereas the stresses for the tensile bond strength

are transmitted through the adhesive to the interface. The path of a fracture placed under tension will therefore pass through the weakest areas in the bulk of the adhesive or the interface. One problem with tensile tests is that the force is transmitted Crenolanib through the body of the adhesive, and partial cohesive failure, rather than interfacial failure, often occurs [38]. The consequent variation among specimens might obscure the interfacial bond strength. When a resin composite bonded to a flat dentin surface

is loaded in tension or shear, the distribution of stresses along the interface is extremely irregular. For shear strengths, Fludarabine the stress is concentrated at the interface, and the fracture path will not readily deviate unless there is a major flaw either in the adhesive or at the dentin surface [36], [37] and [38]. The shear bond strength might be related to the elastic modulus of the adhesive. Increasing the modulus of elasticity will result in a more uniform distribution of stress over the bonded area, and avoid a concentration of stress at the point of load application. An extremely low elastic modulus will cause the fracture to have a peeling character rather than a shear character. The elastic modulus of restoratives has been reported to increase roughly in line with increasing shear bond strength [39]. When determining the shear bond strength, the maximum force is exerted along the interface and, in practice, a more reproducible interfacial fracture is observed, with much less cohesive failure [40]. The shear bond strength of a dentin-bonding system is dependent on the adhesive mechanism; similar results are not expected to be obtained with different adhesive systems. A lapping shear test or a knife-edge test is most commonly used, and a notch effect at the knife-edge tip should be taken into consideration.

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