| Objective:This study analyzed the stress distribution on the residual tooth tissue and the interface between post and dentin to investigate the effects of post with different size and material on restoring the large hard tissue defects of maxillary central incisor using three-dimensional finite element methods.This study provided us an optimal method for restoring large defects of the central incisor by the post and core with optimalized post length and diameter based on different materials to reduce the risk of root fracture and post broken after post and core restoration.Material and method:CBCT was taken to obtain experimental images of maxillary central incisors in DICOM format,Mimics /Geomagic/Abaqus software were used to establish a three-dimensional finite element model for the post-core crown restoration of maxillary central incisors.1.The model of Maxillary central incisor in Mimics(1)The experimental images in DICOM format were imported into Mimics software.(2)Set the threshold range and distinguish different dental tissues according to the threshold size of CT scan images.(3)Regional growth.The approximate range of enamel/dentin/pulp tissues was selected respectively.(4)Separate and extract the fine maxillary central incisor model.(5)The maxillary central incisor model was optimized.2.Reconstructing the maxillary central incisor model and using the mesh doctor function for mesh repair in Geomagic.3.Establishment of post-core crown repair model in Abaqus(1)Using the model editing functions in Abaqus to generate crown,root,shoulder,periodontal ligament,alveolar bone,post and core and other parts,and complete assembly of all parts of the model;(2)Selecting C3D4 cell type to divide the grid;(3)Setting experimental mechanical hypothesis;(4)Setting boundary condition constraints;(5)Experimental mechanical loading;(6)Setting the analysis Step in the Step module;(7)Submitting the work for analysis and calculation.Based on this model,the Von Mises stress peak and stress distribution law of residual dentin,post and core,and post-to-dentin interface after different materials restoration were studied.Result:1.The three-dimensional finite element model of the maxillary central incisor repaired by post-core crown after root canal treatment of a large area of defects was successfully established,including the complete crown,dentin,shoulder,post-core,periodontal membrane and alveolar bone.2.Three kinds of post and core materials restore the peak stress of the maxillary central incisor roots from large to small: quartz fiber posts> titanium posts> cast cobalt-chromium alloy posts.Peak stress peaks from large to small: cast cobalt-chromium alloy posts> pure Titanium post> Quartz fiber post.3.The stress distribution at the interface between the post and dentin was the most uniform after the repair of the quartz fiber post,followed by the pure titanium post,and the stress at the interface between the post and the dentin was most concentrated after the cobalt-chromium alloy repair.4.Cobalt chromium alloy posts:In the range of pile diameter of 1.25 mm and pile length of 5-11 mm,the peak values ??of Von Mises stress of the roots was: 28.73 Mpa ～ 29.39Mpa;In the range of pile diameter of 1.25 mm and pile length of 5-11 mm,the peak values of Von Mises stress of the roots was: 28.63Mpa～29.64Mpa;In the range of pile diameter of 1.25 mm and pile length of 5-11 mm,the peak values of Von Mises stress of the roots was:26.79Mpa～28.88Mpa;In the range of pile diameter of 1.5mm and pile length of 5-11 mm,the peak values of Von Mises stress of the roots was:26.44Mpa～28.86Mpa;In the range of pile diameter of 1.75 mm and pile length of 5-11 mm,the peak values of Von Mises stress of the roots was:24.83Mpa～28.62Mpa;In the range of pile diameter of 2.5mm and pile length of 5-11 mm,the peak values of Von Mises stress of the roots was: 24.81Mpa～29.44Mpa;In the range of pile diameter of 2.75 mm and apile length of 5-11 mm,the peak Von Mises stress peaks of the roots was:26.99Mpa～36.4Mpa.From the above data,it can be seen that the stress was minimal and the stress distribution was more uniform in the range of 2.5mm diameter of the pile,which was about 2/5 of the width of the root diameter,and 9mm diameter of the pile,which was about 3/5 of the root length.5.Quartz Fiber Posts:In the range of pile diameter of 1.25 mm and pile length of 5-11 mm,the peak values ??of the Von Mises stress of the roots was: 29.68Mpa～29.9Mpa;In the range of pile diameter 1.5mm and pile length 5-11 mm,the peak value of tooth Von Mises stress was:30.2Mpa ～ 30.48Mpa;In the range of pile diameter of 1.75 mm and pile length of5-11 mm,the peak values of the Von Mises stress of the roots was:29.08 Mpa ～33.98Mpa;In the range of pile diameter 2mm and pile length 5-11 mm,the peak value of tooth Von Mises stress was:29.69 Mpa ～ 30.25Mpa;In the range of pile diameter2.25 mm and pile length 5-11 mm,the peak value of Von Mises stress of tooth root was:27.79Mpa～29.23Mpa;In the range of pile diameter of 2.5mm and pile length of5-11 mm,the peak values of Von Mises stress of the root was: 29.95Mpa～31.31Mpa;In the range of pile diameter of 2.75 mm and pile length of 5-11 mm,the peak Von Mises stress peaks of the roots was:29.7Mpa～30.32 Mpa.From the above data,the quartz fiber post had a diameter of 2.25 mm,which was about 1/3 of the root diameter;the length of the post was 9-10 mm,and the peak stress of the root is the smallest in the range of 3 / 5-2/3of the root length.6.Pure titanium post:In the range of pile diameter of 1.25 mm and pile length of 5-11 mm,the peak values ??of Von Mises stress of the roots was: 28.98 Mpa ～ 29.62Mpa;In the range of pile diameter of 1.5mm and pile length of 5-11 mm,the peak value of the Von Mises stress of the tooth roots was:29.86Mpa～30.03Mpa;In the range of 1.75 mm diameter of pile and5-11 mm of pile length,the peak value of Von Mises stress of tooth root was:27.54Mpa～33.27Mpa;In the range of pile diameter 2mm and pile length 5-11 mm,the peak value of tooth Von Mises stress was:27.53Mpa～29.69Mpa;In the range of pile diameter 2.25 mm and pile length 5-11 mm,the peak value of Von Mises stress of tooth root was:26.2Mpa～28.82Mpa;In the range of pile diameter of 2.5mm and pile length of 5-11 mm,the peak values of Von Mises stress of the roots was:26.55 Mpa ～29.43Mpa;In the range of pile diameter of 2.75 mm and pile length of 5-11 mm,the peak Von Mises stress peaks of the roots was:26.4Mpa～29.42 Mpa.From the above data,the quartz fiber post had a diameter of 2.25 mm,which was about 1/3 of the root diameter;the length of the post was 9-11 mm,and the peak stress of the root was the smallest in the range of 3 / 5 of the root length.Conclusion:1.In this experiment,the three-dimensional finite element method was used to establish the post-core crown restoration model of maxillary central incisors,and load was added and the above experimental analysis was conducted,which can providetheoretical basis and guidance for patients to design personalized schemes and improve the success rate of post-core crown restoration.2.With the increase of the elastic modulus of post-core material,the peak value of residual dentin stress gradually decreases,and the cast cobalt-chromium alloy post <pure titanium post < quartz fiber post.3.With the increase of the elastic modulus of post-core material,the stress peaks on the post-core gradually increase,and the cast cobalt chromium alloy post > pure titanium post> quartz fiber post.4.Cobalt-chromium alloy,fiber pile and pure titanium pile were used to repair the maxillary central incisor with a large area of defects,and the crown stress concentration area was cut into 1/3 and 1/3 of the maxillary central incisor;On the outer surface of the root,the stress was mainly concentrated in the labial side of the root,1/3 of the root.It is recommended to retain more than 1/3 of the tooth tissue in the root of the lip during tooth preparation.5.When the remaining tooth tissue in the tooth neck is sufficient and enough dentin shoulder collar can be obtained,it is recommended to choose the fiber post repair similar to the elastic modulus of dentin.The best restoration range of quartz fiber pile:the diameter of the pile is 1/3 of the width of the root diameter,and the length of the pile is 3/5-2/3 of the root length. |
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