The Different Cementing Of The First Maxillary Molar Restored With In-ceram All-ceramic Crown A Finite Element Analysis Study

Objective: Construct an In-ceram all-ceramic crown model of the first maxillary molar, with three dimensional finite element analysis technique. For the purpose of observing and analyzing the stress distributions during the veneer layer, the core layer and the cement layer in different adhesive conditons, in order to provide guidelines for cementation of the double-layered all-ceramic crowns.Methods: Using the computer tomography (CT) images construct a three dimensional finite element model of the first maxillary molar by applying the MIMICS 10.01 software, then employ the GEOMAGIC to modify the models, at last by use of the CATIA software, the model is separated into six parts: crown(include the core layer and the veneer layer),cement, prepared tooth ,the root of the tooth, periodontal ligament, and alveolar bone.Devide the models into four different groups in accordance with the thickness of the cement(50μm,80μm,110μm and 140μm),each group is sub-divided into three sections according to the type of cement, including the Panavia,the 3M ESPE RelyX ARC,and the zinc phosphate cement. A load is applied to observe the stress distribution of the maximum principal stress in the cement layer, the core layer and the veneer layer.Results: The distribution areas of the maximum principal stress are almost located in the same place, when use different cements or different thick of the cement. Only the values of the stress differ from each other:1. The stress of the layer lies in the positions of the mesio-buccal shoulder and the teeth near occlusal surface from the lingual side; the stress of the core layer located in the inner surface from the colossal side; the stress loads in the veneer layer is applied on the location where the load applied.2. When the cement thickness increases, the maximum principal stress also attends to a rise in the core layer, the venner layer and the cement.3. As the modulus of the cement rises while the thickness of the cement is in the same lever, the maximum principal stress declines in the core layer, and the maximum principal stress increases in the veneer layer and the cement layer.Conclusion:1. Whatever the type and the thickness of the cement are, as long as the load is applied in the same condition, the distribution areas of the maximum principal stress are always the same, but there is a trend due to the load: the distribution areas are more likely to move to the place near the load position.2. When the thickness of the cement grows from 50μm to 140μm,the maximum principal stress seems to increase, indicated that dentists should try to guarantee the accuracy of the ceramic crowns, in order to minimize the maximum principal stress on the double-layered ceramic crowns, which also leads to the improvement of the quality of fracture resistance.3. When use the same thickness of the cement, the high modulus cement makes the maximum principal stress much more higher on the core layer, and the decreases on the veneer layer,. It shows that high modulus cement can prevent the rate of veneer crack, but it also can cause the drop of the fracture resistance.4. When use the same thickness of the cement, the low modulus cement makes the maximum principal stress smaller, it can be a way to improve the reality of the drop of ceramic crown.