Comparação dos ensaios de resistência adesiva por torção e por cisalhamento com fio / A comparison between torsion and wire-loop shear bond strength tests

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

Objective: verify, by finite element analysis (FEA) and laboratorial tests, if the torsion bond strength test is able to lead adhesive interface to fracture under shear stress and if it would be more advantageous than wire-loop shear test. Material and method: for stress analysis by finite element method, the 3D models of both tests consisted of a resin composite cylinder, an adhesive layer and a dentin cylinder with a larger diameter. The specimens were simulated with both conventional and micro sizes, in a 5:1 ratio, except for the adhesive layer, kept in a constant thickness. Two values of elastic modulus were simulated for the composite cylinder (hybrid and flowable). For the shear models, different distances were simulated between the load point and the adhesive interface. The values of maximum principal and maximum shear stresses and the ratio between both types were analyzed along the adhesive interface, as well as the maximum principal vectors direction and the local of stress peaks. For the laboratorial tests, cylinders of hybrid and flowable resin composite, in both micro and conventional sizes, were adhered onto dentin surfaces by means of 3 adhesive systems. The shear load was applied with a metallic wire-loop at distances from the interface based on literature and, for the torsion test, the torque was applied by specific apparatus developed for that. The values of bond strength were submitted to analysis of variance and Tukeys test. Fracture surfaces were analyzed by scan electron microscopy. The frequencies of fracture types were compared by Fishers test and its relationship with bond strength values were verified, as well as the relationship between fracture features and stresses results obtained by FEA. The experimental parameters for comparison between both tests were: ability for detecting significant differences among the 3 adhesives, change of adhesives ranking while varying the test configuration and frequency of fracture types. Results: both tests showed non-uniform stress distribution. It was not noticed a lower sensibility of torsion test results to changes of the test configurations, nor a major ability for detecting significant differences among the adhesive systems than showed the shear test. The torsion test showed to be more difficult to execute and exhibited a higher frequency of cohesive fracture, however, that occurred most of the time in the composite cylinder, while it occurred mainly in dentin in shear test. There was no certainty about the kind of stress that lead to specimen fracture in both tests. Conclusions: although there was no certainty about the kind of stress that lead to specimen fracture and the major difficulty of execution of torsion test, this test exhibited a feature that suggests future studies: the occurrence of cohesive fracture mainly in the composite cylinder, which could be solved, maybe, by reinforcing the cylinder material.

ASSUNTO(S)

interface adesiva torsion test finite element method resistência de união adesiva adhesive bond strength biomechanics shear test ensaio de torção ensaio de cisalhamento biomecânica método dos elementos finitos adhesive interface

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