Purpose: To compare the mechanical behavior (stress load dissipation and/or concentration) of posterior crowns made from Lava Ultimate (LU; 3M ESPE) and IPS e.max CAD (LD; Ivoclar Vivadent) using finite element analysis (FEA).
Materials and Methods: A 3D model of a mandibular first molar was prepared by reducing the occlusal surface by 1 or 2 mm (according to group), the axial walls by 1.5 mm, and with a 0.8-mm–deep shoulder margin as a finish line. A convergence of 6 degrees between opposing walls was set. Subsequently, four 3D crown models were created according to two test groups with two different occlusal thicknesses: (1) LD with 1.0 mm (LD1); (2) LD with 2.0 mm (LD2); (3) LU with 1.0 mm (LU1); and (4) LU with 2.0 mm (LU2). FEA models were constructed using Femap software (Siemens). A load of 200 N was applied in the axial and oblique (20 degrees) directions for each group, and stress dissipation was viewed using NEi Nastran software.
Results: FEA results demonstrated that the LU crowns dissipated the occlusal load to the tooth structure, whereas the LD material concentrated the load inside the crowns. For LU material, the lower the occlusal thickness, the higher the stress concentration inside the crown, and the 2.0-mm occlusal thickness transferred lower stress to the tooth structure. The oblique rather than the vertical load caused an increase in the maximum stress concentration at the shoulder margin and axial walls.
Conclusion: The higher the Young modulus mismatch between the crown material and substrate, the higher the load stress concentration inside the material. The 2-mm occlusal thickness acted by decreasing the load stress to the tooth substrate. Finally, the axial load delivered more favorable stress transmission to the tooth substrate. Crown material and occlusal thickness both affect the mechanical behavior of stress dissipation to the tooth structure.
