Stress Distribution Of The Three-dimensional Post-crown Model With Labial And Lingual Oblique Defects Of The Maxillary Central Incisor: A Finite Element Analysis

Background: With the development and progress of oral medicine technology,the concept of preservation and repair is more emphasized in oral prosthodontics and it is widely accepted by clinicians,thus the preservation and restoration of residual root and crown has become a routine treatment for modern oral prosthodontics.Clinically,dentin ferrule contributes a lot to resistance,retention and edge sealing of post-core crown.It is generally recognized that dentin ferrule should retain the height of 1.5mm.But the maxillary central incisors are prone to be crushed for they are in the front of dental arch.Usually,fracture surfaces of labial and lingual side are irregular,dentin ferrule of two sides are in alternative level or defect,which cause increasing risk of falling or breaking off of the fiber post-core crown.Objective: Defining deficient side ferrule as 0 mm,analyze the stress distribution of the three-dimensional model of maxillary central incisor’s post-core crown with lips and tongue oblique defect through Three-dimensional finite elementt analysis,discussing which fracture section is more meaningful to be retained.Methods: A standard maxillary central incisor is selected,scanned by CBCT and import to Mimics17 software.The Imageware and UG software are used to construct the post-crown model with lips and tongue oblique defect.Limit the dentin ferrule height of the defective side to 0 mm,and group according to the dentin ferrule height of the lip side-the dentin ferrule height of tongue side(0 mm-0 mm、0 mm-0.5 mm、0 mm-1.0 mm、0 mm-1.5 mm、0 mm-2.0mm 、 0.5mm-0mm 、 1.0mm-0mm 、 1.5mm-0mm 、 2.0 mm-0 mm 、 0.5mm-0.5mm、1.0 mm-1.0mm、1.5 mm-1.5 mm、2.0mm-2.0mm).At the junction of 1/3 and central 1/3 of all-ceramic crown,apply a force of 100 N at 45 °to the long axis of the tooth and analyze the Von Mises stress distribution of root dentin、 resin cement layer and fiber post through finite element analysis.Results:(1)Stress distribution of root dentin : In the case of that the dentin collar of the lip and tongue side are intact,if the height of the dentin height increases,the root Von Mises stress gradually become more evenly distributed from being concentrated on the neck and the peak stress gradually decreases.In the case of defective dentin ferrule,the peak value of Von Mises stress of dentin collar at the tongue side or the lip side was smaller than that without the dentin collar;but at the same height,the dentin collar’s stress reduction of tongue side is more obvious,close to the dentin ferrule collar complete group;(2)Stress distribution of fiber post : In the case of that the dentin collar of lip and tongue sides are intact,if the height of the dentin ferrule increases,fiber post’s Von Mises stress gradually increased.In the case of defective dentin ferrule,fiber post’s Von Mises stress of dentin collar at the tongue side or the lip side was larger than that without the dentin collar;And with the increase of the height of the dentin ferruler,the Von Mises stress of fiber post increased.(3)Stress distribution of resin cement layer:If the shoulder collars at the sides of lip and tongue are complete,the Von Mises peak stress value of adhesive layer reduces while the height of shoulder collar increases.If the shoulder collar of dentin is incomplete,even under the circumstances that the tongue side has shoulder collar or the lip side has shoulder collar,the Von Mises peak stress value of adhesive layer reduces comparing to that there is no dentin ferrule.But if the heights are same,the peak stress value of the dentin ferrule at the tongue side reduces substantially,which is close to the reduction under situation of that the dentin ferrule is complete.Conclusion:1.Create accurately a high-precision post core crown model and conduct stress analysis through CBCT scanning,medical imaging control system Mimics software,Imageware software,UG and ANSYS software.2.If the height of the dentin ferrule increases,the Von Mises stress concentration of the root dentin and adhesive layer will reduces.And the peak stress value will also reduce.The incomplete dentin ferrule still has positive effect on the fixing of prosthesis and stress resistance.3.The increase of the dentin shoulder collar height will increase the stress of the Von Mises of the fiber,and the Von Mises stress of the root dental tissue and the adhesive layer is dispersed.4.If the dentin ferrule is incomplete,the dentin ferrule of the tongue side contributes more for diffusing the Von Mises stress of the root dental tissues and adhesive layer comparing with the dentin ferrule of the lip side.The increase of the height of tongue side dentin ferrule will do more good for the prosthesis to resist stress and be fixed.If minimum 0.5-1.0mm of tongue side shoulder collar is kept,the effect will be more obvious.