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The objective of this study was to evaluate the influence of bracket base mesh geometry on the stresses generated in the bracket-cement-tooth continuum by a shear/peel load case. A validated three- dimensional finite element model of the bracket-cement-tooth system was constructed consisting of 15,324 nodes and 2971 finite elements. Cement geometric and physical properties were held constant and bracket base geometry was varied, representing a variety of single-mesh configurations and 1 double-mesh design. For the single-mesh designs, increasing wire diameter (100-400 μm) resulted in a decrease in enamel and cement stresses. Increases in wire mesh spacing (200-750 μm) increased the major principal stress recorded in the enamel and adhesive at all wire diameters. Within the bracket, the major principal stress increased significantly at wire spacing above 400-500 μm. However, within the impregnated wire mesh (IWM), the major principal stress decreased as wire space increased. When the double-mesh bracket base was considered, the combined mesh layers resulted in a decrease in the stresses recorded in the most superficial (coarse) mesh layer and an increase in the stresses recorded in the deepest (fine mesh) layer when compared with the single-layer designs in isolation. Modification of single-mesh spacing and wire diameter influences the magnitude and distribution of stresses within the bracket-cement-tooth continuum. The use of a double- mesh design results in a reduction in the stresses recorded in the most superficial mesh. Mesh design influenced stress distribution in this study, primarily by determining the flexibility of the bracket base. [ABSTRACT FROM AUTHOR]

The objective of the investigation was to develop a clinically valid three-dimensional computer model of the orthodontic bracket-cement-tooth continuum, and determine the magnitude and distribution of stresses generated by three different load cases. A three-dimensional finite element model of the bracket-cement-tooth system was constructed consisting of 15324 nodes and 2971 finite elements. The stresses induced in the bracket-tooth interface by a masticatory load, a peel force and a twisting couple were recorded. The maximum principal stresses resulting from occlusal and 'twisting' forces are distributed toward the lute periphery. Peel forces, applied to the bracket tie wing, are concentrated beneath the bracket stem. Twisting forces result in the highest enamel stresses. The quality of orthodontic attachment can be explained by the magnitude and distribution of major principal stresses within the cement and impregnated bracket base. Shear and shear/peel forces are most likely to induce crack propagation within the adhesive layer. However, when a twisting action is used to remove orthodontic brackets, enamel failure is most likely. A clearer insight into the complexity of the bracket-cement-tooth system has been provided by numerical and finite element investigations. Further investigations, evaluating the influence of bracket base designs and orthodontic cement physical and geometric properties are indicated. [ABSTRACT FROM AUTHOR]