The aim of this study was to investigate the effects of geometry, thickness, and material on damage mechanics of porcelain fused to metal restorations using numerical method. Extended finite element method (XFEM) was employed to assess the critical loads to mark either the onset of radial cracks at the porcelain undersurface or plastic deformation at the metal top surface, as the two damage modes in dental prostheses. The models contained a brittle outerlayer (porcelain)/metal (Pd/Co/Au alloys) core/dentin substrate trilayer system which were indented by a tungsten-carbide hemisphere. In this study, cylinder and tapered cylinder shapes were created as two different geometries, which the tapered cylinder model was close to the real crown. XFEM not only has the ability to calculate crack initiation load, but also can solve crack propagation problems. The whole thickness of both metal and porcelain was presumed to be 1.5 mm. It was taken from the finite element analyses that harder and stiffer metal core is more resistant to radial crack nucleation. Additionally, it can be concluded that metal with thinner layers are more susceptible to radial cracking. In all models, tapered cylinder geometry has higher critical loads to approach both damage modes. The optimum porcelain layer thickness is offered to be 0.5 mm. Dental crown like structure geometry is an effective parameter. Moreover, metal layer should not be very thin in order to avoid radial cracking. Finally, metal stiffness is better to be high to postpone nucleation of radial cracks.

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