Calculation Of Bond Strengths In Metal-ceramic Systems Using Finite And Infinite Element Stress Analysis

The problem of bond strengths in metal-ceramic systems has been focused on since the method of porcelain-fused-to-metal was used to prosthetics. Despite having established the theoretic of bond strengths in metal-ceramic systems and measures to prevent the bond failure of porcelain-fused-to- metal restoration, the exact definition of bond strengths need to be described. This study calculate the stress distribution in metal-ceramic specimens for the ISO crack initiation test (three-point flexure bond test) using finite and infinite element method, to find the important facts that affect the bonding strength of metal-ceramic systems and provide the academic ground for making porcelain-fused-to-metal restoration in clinic work. The calculation demonstrated the following results:1. In order to precisely calculate the stress distribution of metal-ceramic systems and simulate the manipulation of making porcelain-fused-to-metal restoration, the material parameters according to the manipulation of making porcelain-fused-to-metal restoration should be used.2. For the debonding effect, the shear stress( ?xy) concentration and normal stress( o yy) concentration, along the interfaces occur at the edge of the metal-opaque ceramic interface and near the edge of the opaque-body ceramic interface. The former is the most important fact to the failure ofbond; but the latter could also cause the fraction within the ceramic layer. 3.With regard to the bond stresses o xy and o yy, the immediate vicinity of the point of the initial debonding is subject to a thermal shear/compression system, whereas the load applied in the bond test lead to a shear/tension stress state. The bond experiments therefore produce an offset of the overall shear stress, while the tension load stress is very larger than the compressive thermal stress, when the difference of thermal expansion coefficients between metal and ceramic withinl.O X 10"6. This result indicates a higher probability of failure produced by tension stress rather by shear stress.4.First apply the infinite element method to the stress analysis of bond strengths in metal-ceramic systems, and find the critical stress intensity factor, Klcritlcai=6.509161E+06; force to failure Ffaii=7.14N. 5.With thickness of opaque layer increasing, the stress along opaque-body ceramic interface decrease, but the stress along metal-opaque ceramic interface increase. So, the thickness of opaque should be as thin as possible, in order to keep a certain thickness of body ceramic and obtain aesthetic feeling of restoration as well as improve the bond strengths of metal-ceramic systems.6.Stress concentration occur at labial cervical margin of porcelain-fused-to -metal restoration model, no matter what kind of design the labiocervical margin is in the model. This place is just the area where the fraction of porcelain happens in the porcelain-fused-to-metal restoration. Base on the stress analysis, the model with unit of porcelain to metal at the labiocervical margin is better than the models with porcelain or metal only atlabiocervical margin for upper central incisor restoration.7.Stress magnitudes along the metal-ceramic interface enhance with theangle of loading force with axle of central incisor growing. The normalocclusal force at the angle of 45?loading, cant lead the fraction of porcelainfrom metal. But with the angle increase, for example deep overbite, thesame occlusal force may cause the failure of porcelain-fused-to- metalrestoration.