Methods: Three different occlusal cavity shapes were simulated in disc specimens (Model A: 2 mm occlusal, 1.5 mm cervical diameter; Model B: 1.75 mm occlusal, 1.5 mm cervical diameter; Model C: 1.5 mm occlusal, 1.5 mm cervical diameter). Quarter sizes of 3D FE specimen models of 4.0×4.0×1.25 mm3 were constructed. In order to avoid quantitative differences in the stress value in the models, models were derived from a single mapping mesh pattern that generated 47, 182 element and 66,853 nodes. Used materials were composite (Filtek Z250, 3M ESPE), bonding agent (Adper Scotchbond Multi-Purpose, 3M ESPE) and dentin as an isotropic material. Load conditions consisted of subjecting a press of 4 MPa to the top of composite disc. The postprocessing files allowed the calculation of the maximum principal stress, minimum principal stress and displacement within the disc specimens and stresses at the bonding layer. FE model construction and analysis were performed on PC workstation (Precision Work Station 670, Dell Inc.) using FE analysis program (ANSYS 10 Sp, ANSYS Inc.).
Results: Compressive stress concentrations were located equally in the bottom interface edge of dentin. Tensile stress was located top area of dentin and at the half of lower side of composite under the loading point in all of FE models. However, the range of stress distribution and stress values were different. Compressive and tensile stress of model A was the highest. Displacement of model A was the highest of the tested design. By increasing the slope, the maximum displacement was also increased.
Conclusions: The FE model revealed differences in displacement and stress between different cavity shaped disc specimens.