An Three-dimensional Finite Element Analysis Of The Stress Conditions Of Different Dentin Shoulder Collar After All-ceramic Post And Crown Repair

Objective:when the maxillary first molar was restored by the all-ceramic materials post-core crown, we use the three dimensional finite element analysis method, in order to compare the stress of the size and the effect of its distribution on the residual dentine which caused by the various different ferrule structure. To provide date for guiding the clinical choice of all-ceramic material of the prosthesis, the prosthesis to maximize its use of function.Methods:Use of212pictures by the preservation of thin-section CT in vitro maxillary first molar income dicom format. The finite element model of the vitro maxillary first molar which the Dentin shoulder collar with varying degrees of defects was set up using the thin-section Computed Tomographic(CT) scanning technology, MIMICS10.01software and the ANSYS software. The model includes all-ceramic crowns, all-ceramic post-core, adhesive layer residual dentine, periodontal membrane, alveolar bone. The study is divided into two parts according to the dentine ferrule height and integrity. The first experiment is divided into four groups(ie:0mm,1mm,1.5mm,2mm), according to the height of dentin shoulder collar. The second experiment is divided into two groups according to the dentin shoulder collar complete:Group1:dentin shoulder collar2mm height, near1/2defects, Group2: dentin shoulder collar2mm heigh, the walls complete. All defects were resorted with all-ceramic post and core, and with five loading:vertical concentrated load600N, six vertical distribution of load600N, vertical partial buccal side load600N,10°partial tongue side load of600N, tongue side of20°chewing load225N. Simulated chewing force analysis to observe the peak value and distribution of the Von mises stress on the residual dentine and adhesives layer.Results:Experiment one:Different heights of the dentin shoulder collar by the all-ceramic post and core crown restored three-dimensional finite element analysis1. Under the five loading,0mm<dentine shoulder collar height≤2mm, the Von mises stress cloud on the all-ceramic crowns and the remaining dentine is basically the same, which radially decreasing to around.But the stress values is different, and with the increase of the dentine ferrule height, the stress values decreasing trend. And maximum yield strength within the scope of all-ceramic crowns. 2. When the dentine ferrule height is Omm, the maximum stress is mainly concentrated in the mesial buccal root of the section; lmm<height<2mm, the maximum stress concentration points to the root side down, in the mesial buccal root1/2.3. Under the five loading, the Von mises stress cloud which on the outer surface of the all-ceramic crowns is basically same, and radially decreasing to around the size of the stress; The maximum stress is mainly concentrated in the central fossa, near the tip of the tongue, cheek tip of the tongue inclined plane, the tongue of the tongue on an inclined plane, but the size of the stress values is different. Seen from the crown surface, when the dentine ferrul height of lmm, the stress distribution of the crown edge is uniform.Experiment two:Incomplete dentin shoulder collar by the all-ceramic post and core crown restored three-dimensional finite element analysis1. Under the five loading, the outer surface of the Von mises stress cloud of the all-ceramic crowns is basically the same in group1and2; group1crowns suffered power value is greater than group2, and in all-ceramic crown maximum yield strength range.2. Group1, the maximum stress concentration on the dentine in the root tip at the mesiobuccal root canal post and core, near the shoulder at the edge on the palatal root.3. The stress on the remaining dentine is less than in group1to group2, within and in the dentine tensile strength range.Conclusion:1. The existence of the dentine shoulder collar, has a protective effect on tooth structure, the use of all-ceramic post and core crown, the need to keep at least lmm of dentin shoulder collar.2. When the vertical force on the all-ceramic post and core crown, the stress is concentrated in the crown loading conditions; When lateralization force, the stress mainly on the functional cusp slope. Prompt clinical tooth preparation should pay attention to the preparation of functional cusp slope, occlusal contact area should be increased in order to blunt cusp form, replace the point contact, surface contact and dispersion stress; should avoid premature contact and occlusal interference, as far as possible scattered occlusal force.3. When the dentine shoulder collar to achieve2mm, near1/2defects do not affect the repair effects. Just pay attention to the mesiobuccal pile of nuclear cutting edge to blunt, to avoid stress concentration.