2006 Volume 49 Issue 5 Pages 574-581
Our previous study showed that microleakage occurred mainly at the incisal margins of the wedgeshaped cervical cavities when flexural load cycling (labio-lingual displacement) was repeatedly applied to the incisal edge of the tooth, whereas it mainly occurred at the apical margins of the U-shaped cavities. Accordingly, stress distribution produced by occlusal forces as well as bond strength to enamel and dentin and polymerization contraction may have an influence on the microleakage pattern. The purpose of this study was to investigate the stresses induced along the cavity walls of cervical resin composite restoration under mechaanical load using 2D finite element analysis. Two finite element models of the incisor were developed: the wedge-shaped cavity model, and the U-shaped cavity model. These finite element models were developed using a finite element analysis software package "Ansys 7.0". Enamel, dentin and resin-based composite were assigned Young's moduli of 41,400, 18,600 and 10,000 MPa, respectively, and Poisson's ratios of 0.3 and 0.3, respectively. The pulp chamber was modeled as a void bacause of its negligibly low Young's modulus. Meshing was carried out using linear, eight-node isoparametric elements. The wedge-shaped cavity model consisted of 3,047 nodes and 907 elements. The U-shaped cavity model consisted of 4,106 nodes and 1,289 elements. All the nodes in the bottom row of the model, 2mm below the apical margin of the restoration, were fixed in both the X and Y directions. Labio-lingual displacement of 1 mm was applied to the incisal edge of the models. The materials comprising the model were assumed to be isotropic and homogeneous. Outputs were presented in the form of stress contour plots of these models. The shear and normal stresses generated at the adhesive interfaces were calculated. The stress contour in the wedge-shaped cavity was similarly observed in the tooth with the U-shaped cavity, excluding around the cavity. The incisal wall of the wedge-shaped cavity had greater normal (tensile) stress than the apical wall. The incisal wall of the U-shaped cavity had less normal (tensile) stress than the apical wall. The findings of this study have indicated that the stress distributions generated at the adhesive interfaces by mechanical load depend on the cavity forms. Moreover, the findings suggest that tensile stress participates in bonding failure and plays an important role in microleakage.
