Three-dimentional Finite Element Analysis On Mandibular First Molar With Mesio-Occluso-distal Defect Restored By Inlay And Onlay

Objective:The purpose of this research was to investigate the stress distribution on restoration options and materials for the MOD defect of mandibular first molar.Three-dimentional finite element models restored by onlay with fuctional cusp covered and inlay using composite,lithium-disilicate ceramic Emax,gold materials,with 3M-ESPE Universal,Variolink,Fu-ji ? as adhesive agents respectively to evaluate stress distribution on the restoration,adhesive layer and remaining dental tissues,providing a guideline for the restoration of such kind of tooth defection.Methods:CBCT scanning,Mimics,Rapidform.xor3,Solidworks and other reverse engineering software were used to generate the three-dimentional finite element model of MOD lesion with inlay and onlay restorations.Assembly and mesh generation were created by Abaqus.The initial mandibular first molar was used as a control group.Under vertical or 30 degree oblique direction static loading of 300 N,Von-mises on the restoration,enamel,dental as well as compressive and tensile stresses on the adhesive layer were analyzed respectively.Results:1.For the VM stress in restoration,There were no significant differences between onlay and inlay with the same material under vertical loading.On the effect of restorative material,gold material was lower than composite and Emax.Under oblique loading,onlay was slightly higher than inlay.2.For the VM in enamel,under vertical loading,values were higher in inlay than in onlay and were concentrated at the mesial buccal tip,it was also observed that stresses in gold material were the lowest.Under oblique loading,onlay had slightly higher values than inlay.The VM stresses in each group were lower than those in the control group.3.For the VM in dentin,under vertical loading,the highest stresses were observed in the onlay group but only in the cervical region,none obvious stress concentration were found on the coronal tissues.While in the inlay group,the stresses were concentrated on the functional cusps.Under oblique loading,the VM stresses on inlay and onlay with composite material were greater than the control group.The stress distribution in each group was similar to that in the control group.4.For the compressive and tensile stresses in the adhesive layer,the increasing order of materials in the onlay group under vertical loading was as followed: gold<Emax<composite,while there were no significant differences in the inlay group.In terms of stress distribution,tensile stress occurred in the walls of the cavity and cusp tip in composite inlay and onlay compared with Emax and gold materials.Under oblique loading,compressive stresses were significantly lower than tensile stresses in inlay and onlay group.Conclusions:1.The method to establish the three-dimentional finite element model in this study was efficient,accurate and repeatable comparing with traditional methods,simulating the actual condition in the oral cavity,analyzing the mechanical properties under function.2.For the MOD cavity,stress concentration was obeserved in the exposed functional cusps.The onlay design were able to protect remaining tooth structures.Therefore it is crucial to protect remaining tooth structure while providing enough space for the prosthesis.3.In terms of the effect of materials,there were no significant stress concentration on tooth structures and restorations with the gold material.Tensile and compressive stresses were well distributed in the adhesive layer,which can result in a lasting adhesion.