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 misalig nment of the tensile and shear forces was calculated. Applying a shear load produces significant compressive and tensile stresses in the adhesive laye r. Under ideal conditions of shear loading, the induced tensile stress is o ver 5 times the induced shear stress. The model shows that a tensile load i nduces predominantly tensile stresses in the adhesive layer. The calculatio ns indicate that the tensile test method is a robust testing method with lo w sensitivity to misalignment of the applied load.