| ObjectiveBased on the three-dimensional finite element analysis,we evaluated the effect on the stress distribution of different prosthetic methods of implant-supported posterior single crown under dynamic load in the mandibular premolar.The stress and stress distribution were observed under the masticatory cycle according to the clinical treatment plan to build different implant-supported crowns of models.We observed whether opening the hole in the occlusal surface will influence the stress distribution of implant-supported crowns,and provided the reference for clinical choices of prosthetic methods of implant-supported crowns in biomecharnics perspective.Materials and Methods1.Three-dimensional finite element modelsA mandibular specimen with complete dentition of a healthy adult was chosen to build the model.The three-dimensional entity Imodel of the mandibular and implant-supported posterior crowns was obtained via Mimics19.0 software,Geomagic Studio 2012 software,CATIA V5R19 software from CT scanning the mandibular specimen.The implant-supported posterior crowns model consisted of implant,abutment,crown and agent.According to different designs of the crown,two experimental groups were established as follows:traditional implant-supported zirconium-oxide crown(A),implant-supported zirconia crown with a hole in the occlusal surface(B).2.Stress analysis of different finite element modelsEach group model was imported:into the finite element analysis software Ansys 18.0 software,divided mesh automatically,set the assumptions,boundary conditions and parameters.Dynamic loads of 250 N were applied from different directions on the buccal and lingual cusps of implant-supported crown of the second mandibular premolar to simulate the masticatory cycle for 0.875s.There were five stages:0.000～0.130s(Ⅰ):the stress was loaded with no contact,0.130～0.150s(II):the stress was loaded on the buccal cusp and the direction was perpendicular to the occlusal surface,0.150～0.260s(Ⅲ):the stress was loaded on the buccal inclined surface of the buccal cusp and the direction was from the buccal side to the lingual side with 45°,0.260～0.300s(IV):the stress was loaded on the lingual inclined surface of the buccal cusp and the direction was from the lingual side to the buccal side with 45。,0.300～0.875s(Ⅳ):the stress was unloaded with no contact.We chose the Von Mises stress and maximum principal stress of the implant,bone,abutment,crown and the agent as analysis indicators for the finite element analysis.Results1.During the process of dynamic loading,the maximum Von Mises stress value and peak value of the maximum principal stress of crown,agent,abutment,implant and bone of each group followed the order that the stress value increased continuously from 0.130s to 0.300s.The tongue to buccal loading created the maximum stress in a masticatory cycle.2.The maximum Von Mises stress value and peak value of the maximum principal stress of crown,agent,abutment,implant and bone of model B were all higher than that of model A.3.The stress of the crown of model A was concentrated at the loading position and the cervical margin.The loading position,cervical margin and the margin of the hole in occlusal surface were the stress concentration zone of the crown of model B.The peak value of Von Mises stress of the crown of model B was 128.75MPa and increased by 100%than that of model A.The lingual cervical margin of model A was the tensile stress concentration zone,and the peak value of maximum tensile stress were 57.53MPa and decreased by 7%than that of model B.The peak value of maximum tensile stress of model B was 69.54MPa,and located at the margin of the hole in the occlusal surface.whether it was model A or model B,the peak value of stress of crowns were less than that stress extremum of zirconia material.4.The stress of the agent of model A was concentrated at the cervical margin.The cervical margin and the surrounding of the abutment superior border were the stress concentration zone of the agent of model B.The peak value of Von Mises stress of the agent of model B was 83.94MPa and increased by 40%than that of model A.The peak value of maximum tensile stress of two model located at the lingual cervical margin.The peak value of maximum tensile stress of model B was 65.58MPa and increased by 13%than that of model A.5.The stress distribution of the abutment,implant and bone of model A was similar to that of model B.The stress of the abutment of model A and model B concentrated at cervical part.The peak value of Von Mises stress of the abutment of model B increased by 5%than that of model A.The cervical part of the implant was the stress concentration zone of the implant and bone.The peak value of Von Mises stress and the maximum tensile stress of the implant of model B increased by 6%and 12%respectively than that of model A.Conclusion1.Off-axial load induces more stress than vertical load and creates the maximum stress in a masticatory cycle.The dynamic load has a greater influence on the stress distribution of different implant restorations,among which the stress value of the implant-supported crown with a hole in the occlusal surface is larger,and it’s easier to break in the process of using.2.The hole in the occlusal surface of the implant-supported crown has a greater influence on the stress distribution of crown,and the value of stress increases obviously.The lingual cervical margin and the margin of the hole in the occlusal surface of crowns are the tensile stress concentration area,which are prone to fracture.Therefore,we should pay more attention to the design and production of cervical margin and the margin of the hole in the occlusal surface of crowns in the clinical application,especially the design and adjustment of the occlusion.3.The hole in the occlusal surface of the implant-supported crown has a greater influence on the stress distribution of agent.The cervical margin and the surrounding of the abutment superior border are the tensile stress concentration area of agent,which are prone to produce stress fatigue and increase the risk of failure of crowns.4.The hole in the occlusal surface of the implant-supported crown has little influence on the change rule and distribution of the stress concentration area of the implant and bone. |
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