Ebrahim Maghami - Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, US
Ehsan Homaei - Hamm Dental Zahntechnik, Appenweier, Germany

This study investigated the impacts of geometry, thickness, and material on damage growth in a porcelain-metal restoration structure by utilizing a computational approach. Extended finite element method (XFEM) was used to find the critical loads causing the nucleation of radial cracks at the porcelain undersurface. Plastic deformation also was considered at the metal above the surface as another damage mechanism. The dental system consisted of a brittle outerlayer (porcelain)/metal (Pd/Co/Au alloys)-core/dentin-substrate trilayer system. A tungsten-carbide hemisphere as an indenter was used to apply a compressive loading on the structure. In addition, two different geometries were created to present the dental structure, cylinder, and tapered cylinder. The results showed that a harder and stiffer metal core can resist the initiation of radial cracks. It was also observed that the metal with thinner layers is more vulnerable to radial cracking. In all simulations, the tapered cylinder geometry showed to have higher critical loads in both damage modes. The optimum thickness for the porcelain layer was suggested to be ۰.۵ mm. The geometry of dental crown-like structures was found to be an important factor in damage initiation. The findings also proposed that the metal layer should not be designed very thin in order to prevent the formation of radial cracks. This numerical investigation also recommended that the stiffness of the metal layer is better to keep higher compared to other layers to hinder the initiation of radial cracks.

Metal-ceramic structure, Restoration geometry, Plastic deformation, Radial cracking, XFEM