Influence Of Bonding Layer With Different Types And Thickness On Stress Distribution Of Post And Core Restored Maxillary Central Incisor

Post and core applications are generally used in the restoration of endodontically treated teeth for retention of the full crown, while root fracture is one of the common complications .A host of study are available for how to reinforce the remaining tooth structure .They are often focused on different post materials, core materials, post diameters and so on ,while the effect of cement between post and tooth structure is usually ignored.Cement is mainly used for the retention of the post ,at the same time it changes the stress distribution of the remaining tooth structure. The latter point is more important because the post may be re-cemented if it is dislodged. If the tooth is fractured , the whole tooth usually has to be extracted. Functional stress transfers from the post to dentin through cement layer, cement may play the role as a buffer .This study compared the influence of the cement layer with different thickness on the post and core restored maxillary central incisor using three dimensional finite element stress analysis . And then a in vitro study was used to compare the fracture resistance of pulpless teeth restored with post-and-core systems .The posts were cemented into roots with two different cements: Super-bond C &B and zinc phosphate cement.Part I: Three dimensional finite element stress analysis of stress distribution in the post and core restored maxillary central incisor with different thickness of the bonding layerMaterials and Methods: 4 three-dimensional finite element analysis models of the post and core restored maxillary central incisor were built .The following parameter affecting corono-radicular restoration was studied: 4 levels of cement thickness . The 4 levels of cement thickness were 50μm , 100μm ,150μm , 200μm ,A porcelain-fused-to-metal crown covered each of the models and received a 45° oblique occlusal load at a constant intensity of lOON.The software computed the stress for each of the models.Results: Whatever the type of stress , the greatest stress was observed in the cervical region ,regardless of the model. The stress in dentin had an increasing tendency with the increase of the bonding layer .Conclusions: Within the limitations of this study , it was confirmed that all simulated reconstructed teeth were more subjected to stress in the cervical region. In clinic work , the bonding layer between the canal and the post should be as thin as possible to avoid the high stress concentration in dentin.Part II: In vitro study of the fracture resistance of pulpless teeth restored with post-and-core systems using two different cements .Materials and Methods: 16 maxillary central incisors were used in this study and were divided into 2 equal groups. Each group was assigned to a different cementation system at random. The 2 cementation systems used were: Super-bond C &B and zinc phosphate cement. The crowns of these teeth were removed and root canal therapy were done on each root, which were then prepared to receive cast post and core and complete crown restoration. The samples were then applied loads at an angle of 45 degrees and measured with a universal testing machine...