Tensile and shear stresses in the orthodontic attachment adhesive layer with 3D finite element analysis

The tests commonly used for the evaluation of orthodontic adhesives measure tensile and shear bond strength. The two methods were compared with finite element analysis using a three-dimensional model and the effect of misalignment of the tensile and shear forces was calculated. Applying a shear load produces significant compressive and tensile stresses in the adhesive layer. Under ideal conditions of shear loading, the induced tensile stress is over 5 times the induced shear stress. The model shows that a tensile load induces predominantly tensile stresses in the adhesive layer. The calculations indicate that the tensile test method is a robust testing method with low sensitivity to misalignment of the applied load.