The Suggestions Based On Finite Element Analysis To Make The All-Ceramic Crown By CAD/CAM When The Butment Or The Post-and-core Is Nonstandard

Objective: In the clinical practice, there always are some errors in the toothpreparation for all-ceramic crown (especially the excessive cutting in the incisal anglesof anterior teeth and cuspis of molar teeth), and because of manual operation，thepost-and-core is also hard to avoid it. So when we make all-ceramic crowns byCAD/CAM, we can not ensure that veneer and core thicknesses are bothwell-distributed。 How to deal with it？In order to give suggestions reliability for that,this experiment under the premise of using a computer aided modeling technology,designs the ideal model and the actual model, and uses computer modeling to create thefirst mandibular molar model, in the standardization under the premise of otherconditions, applies2d finite element analysis method to the analysis for the stress of theall-ceramic crown with the variation of homogeneous of veneer and core thicknesses.In order to determine the shape of porcelain, and increase the whole structure strengthof the all-ceramic crown.Methods: using the RFPA and DeepComp1800super parallel computer，set upthe2-d numerical study model of the first molar mandible. Those models are dividedinto two groups: the metal post-and-core group and the dentine group. Each group isdivided into three kinds: ideal type, veneer and core thicknesses are bothwell-distributed；the second type，core thicknesses are well-distributed；the third type，veneer thicknesses are well-distributed. All six designs (2*3) are stressed in theocclusal surfaces, loading from0Newton until any porcelain layer failure. Analysethose models with RFPA，compare different models of the damage location and themagnitude of force.Results: the results show that, in the metal post-and-core group, damaged startfrom the surface layer of porcelain; the damaged load of the first type is621.72N, the damaged load of the second type is600.6N, the damaged load of the third type is618.6N.But in the dentine group, damage began from internal,；the damaged load of thefirst type is166.17N, the damaged load of the second type is120.41N, the damagedload of the third type is146.32N.Conclusion:1The all-ceramic crown based on metal post-and-core can acceptmore stress than based on the dentine, and the first damage start from the surface layerof porcelain;2In the first group，the second type and the third type are nearly same inloading capacity.3Base on the result of the second group，we suggest to increase thecore thicknesses and ensure the homogeneity of the veneer when making the all-ceramic crown based on the dentine。 At the same time, this experiment can onlyprovide suggestions, but not be as an academic basis to help to establish standard ofconduct. If need formal promotion to the clinical, further studies are required...