Three-Dimensional Finite Analysis Of Different Repair Methods For BO Defects Of The Mandibular First Molar

ObjectiveThis simulation study was designed to compare the effect of different restoration methods on stress transmission to dental tissues. Seven three-dimensional finite element models were created,each representing a tooth embedded in a bony medium. The following parameters affecting the stress were studied:inlayⅠ,inlayⅡ(inlay with resin composite core),onlayⅠ(only buccal cuspid coverage),onlayⅡ(both cuspid coverage), crown and post-core crown.To search for a relatively reasonable prosthodontic design which can result in the most homogeneous stress and stain distributions under two different loads. Materials and MethodsChose a female volunteer with normal occlusions and without tooth abrasion and mandibular alveolar bone absorption. The tomography date of the mandibular first molar and their supporting tissues were obtained by CBCT scanner.Mimics software was used to read and deal with tomography data,Geomagic software to modify precisely,Solidworks software to assemble all of the modules and Ansys Workbench software to divide gridding.The acquirement of six different restoration models were completed by modifying the shape,which simulated the BO defect of the mandibular first molar having done the root canal therapy.Six repair methods included inlayⅠ,inlayⅠ(inlay with resin composite core),onlayⅠ(only buccal cuspid coverage),onlayⅠ(both cuspids coverage),crown and post-core crown.And the material of restorations was IPS e.max CAD ceramic.The vertical load of 50 N located in the middle of mesial and distal marginal ridge, the middle pit and two buccal cusps. The oblique load of 100 N and 60°were applied at one point of buccal inclined plane of two buccal cusps separately. Simulated occlusal force,obtained stress figures of the models and calculated Maximum Principal Stress and Equivalent stress. ResultsEstablished the 3-D finite element models of mandibular first molar with normal structure and the BO defect of molar treated with root canal therapy which consisted of ceramic inlay,ceramic onlay,ceramic crown,dentin,gutta percha,composite resin,glass fiber post,bonding layer,periodontal membrane and alveolar bone.The normal mandibular first molar model:Under vertical and oblique load,the stress of enamel mainly concentrated on the area loading bite force.And the stress of dental mainly concentrated on the cervix and root apical region.While the peak focused on buccal side of distal root apical region under vertical load.Under oblique load,the stress of dental mainly evidenced at the lingual side of mesial root apical region.The comparison in all restoration models :Under vertical load,the stress of enamel mainly concentrated on the area loading bite force.And the changes in the equivalent extreme stress values of enamel:inlayⅡ>inlayⅠ>onlayⅠ>onlayⅡ.The dental equivalent extreme stress in inlayⅠ,inlay Ⅰ,crown and post-core crown models recorded at the buccal side of distal root apical region.While the dental equivalent extreme stress in onlay and onlay models recorded at the buccalⅠ Ⅰ-pulp corner. The variation in the equivalent extreme stress values of dental:onlayⅠ> onlayⅠ>crown>post-core crown> inlayⅠ>inlayⅠ.In all models the maximum principal stress values of dental noticed at the buccal side of disal root apical region and the stress extreme values varied slightly.Under oblique load,the stress of enamel in all models varied differently.and the changes in the equivalent extreme stress values:onlayⅠ>inlayⅠ>inlayⅠ> onlayⅠ.The equivalent extreme stress of dental in onlay model concentrated on the bottom of pulp chamber,while other five models Ⅰconcentrated on the lingual side of mesial root apical region.Meanwhile the changes in the equivalent extreme stress values of dental in all models:onlayⅠ>onlayⅠ> post-core crown>crown>inlayⅠ>inlayⅠ.The maximum principal extreme stress of dental in inlayⅠ,onlayⅠand onlayⅠmodels evidenced at the buccal-pulp corner.And that in inlayⅠ,crown and post-core crown models evidenced at lingual side of mesial root apical region.The variations in the maximum principal extreme stress values of dental in all models:onlayⅠ>onlayⅠ>inlayⅠ>inlayⅠ>post-core crown>crown. Conclusions1. It was fast and valid that using modeling approach of CBCT scan combined with reverse engineering software Mimics and Geomagic, modeling software Solidworks, and the finite element analysis software Ansys Workbench to build a 3-D finite element model.And then the normal mandibular first molar model and the different repair models of the BO defect of mandibular first molar with root canal therapy possessed good geometrical and mechanical similarity.2. For the BO defect of the mandibular first molar with root canal therapy, the IPS e.max CAD crown and the glass fiber post-core IPS e.max CAD crown can result in the most rational stress and strain distribution.3. The glass fiber post does not change the value and distribution of stress and stain.4. When processed in root canal therapy, reserve the dentin at the bottom of the pulp chamber to the greatest extent.