Effect Of Different Post And Core Materials And Ferrule Design On Stress Distribution Of Restored Root

Objectives:The’ferrule effect’ is a long-standing, accepted concept in dentistry and isafoundation principle for the restoration of teeth that have suffered advanced structure loss.In order to harvest enough ferrule height, lengthening thecrown of a tooth with minimalsupragingival toothstructure may involveadditional surgicalremoval of tissue so as to alter the ratio of crown and root. Besides, different post and core materials have different mechanical properties, and would make a difference in restorations. This study aims to get a better treatment plan by evaluating the effect of ferrule design and post systems on endodontically treated root.Materials and Methods:Measure the dentin thickness of30maxillary premolars after post preparation by using anatomical method, and the measurement sites were selected at buccal, lingual, mesial and distal areas of the root on the level of1mm above cementum-enamel junction(CEJ), CEJ and2mm,4mm,6mm,8mm,10mm,12mm below CEJ. Theywere measured three times and averaged.Reconstruct the root model by PRO/ENGINEER software based on the former data, and modify the root to gain different ferrule height. Then modelsof fiber reinforced post and composite resin core were made respectively while metal post and core model was madeas a whole one. Reconstruct the cortical bone and trabecular bone as the constrict part. All the models were fit closely, and the axes of post and tooth were congruent.20models were harvested in this method, and were divided into ABCDE groups respectively according the0mm,0.5mm,1.0mm,1.5mm,2.0mm ferrule. The four models in each group were restored with glass fiber reinforced post and composite resin core(GFP), Nickel-chromium (Ni-Cr), Titanium(Ti) and gold alloy(Au) post systems respectively. A100N static load was applied in the contact area of the buccal and lingual cusps at a30°angle, and maximum principal stress and vonMisesstress distribution pattern were analyzedusing ANSYS.Results:The value of both vonMises and maximum principal stress are lowest in0.5mm ferrule. The stress distribution is more even in GFP group than in metal groups. The stress concentration of GFP group is mainly in root cervical areas while that in metal groups is mainly in both cervical and post apical areas. With regard to metal groups, Ni-Cr group holds the largest stress value, and the Au group holds the least. The stress value of GFP group is only19.4%higher than metal groups on average in the cervical area. On the contrary, the stress value of metal groups is265.0%higher than GFP group on average in the post apical area.Conclusions:①ith regard to endodonticallytreated root of maxillary premolar, the best ferrule height is0.5mm, so there is no need to conduct crown lengthening surgery to get longer ferrule height.②With regard to endodontically treated root of maxillary premolar, the best post and core material is glass fiber reinforced post and composite resin core, following by gold alloy and Titanium in turn. Ni-Cr alloy should be excluded in this condition.③The most possible fracture area of glass fiber reinforced post restored root is cervical area while that of metal restored root is both cervical and post apical areas and the latter is more susceptible.