| Purpose:The purpose of this finite element study was to establish model of extensively defected endodontically treated molar restored with endo-onlay and endocrown,and to analyze the influence of different height of cement layer.Hopefully a more optimized scheme by comparing the mechanical effects of different prosthesis designs can provide theoretical guidance for clinical applications.Methods:The mandibular second molar was extracted because of periodontal disease and it was scanned by Micro-CT.Software used to establish the model of the mandibular second molar and its periodontal tissue included MIMICS,Geomagic and CATIA.Based on this,a proximal-occlusal defect and its restoration with endo-onlay or endocrown was created.The two kinds of restorations were further divided into three groups according to different heights of the cement layer relative to root canal orifice,namely-1,0 and +1mm groups,and there were 6 groups in total.Then,the finite element model was established after meshing the model with ANSYS software,and the vertical and horizontal physiological loads were simulated.The vertical load was300 N,acting on the average of the proximal and distal buccal tips,fossa central and fossa distal.The oblique load was 150 N,acting on the average of the midpoint of the oblique plane of the proximal and distal buccal tips,and the direction was 45° with the long axis of the tooth.After analysis,the peak value of von Mises stress and the output image of stress distribution nephogram were showed.Results:1.The peak values of von Mises stress was analyzed.Under vertical load,the peak values were lower than the tensile strength of dentin at all three cement levels.Among them,the peak stress of the endo-onlay was lower at-1mm and +1mm,and the peak stress of the endocrown was lower at 0mm.Under lateral loading,the Von Mises stress peaks of endo-onlay in +1mm group and endocrown in 0 and +1mm group were both higher than the minimum value but lower than the maximum value of the dentin’s tensile strength range.The peak value of Von Mises was lower than that of vertical load at endo-onlay in-1mm and 0mm group and endocrown in-1mm group.2.The stress distribution cloud map showed that under vertical load,the stress concentration of the +1mm group of both endo-onlay and endocrown was located in the pulp chamber wall.In contrast,the stress concentration at the pulp chamber floor was more obvious in the-1 mm and 0mm groups of the two prostheses.The stress concentration area of the endo-onlay was located at the apex.Under oblique load,stress concentration appeared on the shoulder plane of-1 and 0mm endo-onlay and-1mm endocrown,while the stress concentration area of +1mm endo-onlay and 0 and+1mm endocrown was still located on the wall of the pulp chamber.Conclusions:1.Both CAD/CAM over-onnlay and endocrown can be used to restore extensive proximal-occlusal defect of endodontically treated posterior teeth,but they should be designed appropriately to flatten the cusp to avoid the risk of tooth fracture under oblique load.2.Compared with over-onlay,the endocrown,which covers occlusal surface,does not show obvious advantages of protecting the tooth in the restoration of largly proximal-occlusal defect of endodontically molar.3.Both the endo-oninlay and endocrown achieve a better restoration effect when basing is of the height of 1mm below the root canal plane.Compared with the basing height of-1 and 0mm,It is also more beneficial to reduce the risk of tooth fracture under oblique force. |
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