| Objective:Three dimensional finite element analysis was used to compare the stress distribution of the three restorations of the edentulous jaw with the traditional complete denture,the two implant-supported overdenture connected by the Ball cap attachment,and the two implant-supported overdenture connected by the Locator attachment.The bone mechanics analysis of the posterior alveolar ridge,the implant neck and the cortical surrounding the implant neck under severe absorption were used as the experimental elements to provide reference for the development of the clinical restoration plan of the edentulous jaw under severe absorption.Method:1 CBCT images of edentulous patients with severe mandibular absorption were taken as the research object.Through Mimics Medical 21.0 3D image processing software,3 Shape Trios optical scanner,SolidWorks 2019 drawing software,ANSYS Workbench 2020 engineering design simulation software,the mandible model and the mandibular mucoperiosteal model were established,mandibular traditional complete denture model,implant model,Ball cap model and Locator model as well.2 Assemble mandibular bone model,mucoperiosteal model,mandibular traditional complete denture model,implant,Ball cap and Locator attachment model.Three prosthetic models were established for the edentulous jaw under severe absorption,including the traditional complete denture,2 implant-supported overdenture connected by Ball cap attachment,and 2 implant-supported overdenture connected by Locator attachment.The models were divided into the traditional group,the Ball cap group,and the Locator group.3 The models representing the three restoration methods were respectively loaded according to central occlusal and lateral occlusal in different directions:F1:static vertical load of 63N in the central fossa of the first molar on both sides(perpendicular to the central fossa of the first molar occlusion surface);F2:rightward static lateral load of 120N on the occlusal surface of the right first molar(oblique buccal 300 of the tongue of the right first molar);F3:Left static lateral load of 120N on the occlusal surface of the left first molar(oblique buccal 30° of the tongue of the left first molar).4 The stress nephogram calculated by the three-dimensional finite element method was used to compare the stress distribution of the posterior alveolar ridge,implant neck and surrounding cortical bone in the traditional group,the Ball cap group and the Locator group under vertical and oblique loads,so as to provide reference for the development of the restoration plan of the edentulous jaw under severe clinical absorption.Results:1 Equivalent stress distribution of alveolar ridge in posterior area Under F1 vertical loading,the equivalent stress in the posterior tooth area was traditional group 29.95 MPa>Locator group 24.71 MPa>Ball cap group 22.61 MPa.When F2 was loaded to the right oblique direction,the equivalent stress in the posterior tooth area was Locator group 19.19 MPa>Ball cap group 17.36 MPa>traditional group 13.94 MPa.When F3 was loaded to the left oblique direction,the equivalent stress in the posterior tooth area was Locator group 21.16MPa>Ball cap group 1 6.37MPa>traditional group 13.01MPa.2 Equivalent stress distribution of implant neck When F1 was vertically loaded,the left side of the equivalent stress of implant neck was Locator group 15.5 MPa>Ball cap group 12.56 MPa,the right side was Locator group 21.78 MPa>Ball cap group 17.63 MPa.When F2 was loaded to the right oblique direction,the working side of the equivalent stress on the neck of the implant was Locator group 29.42 MPa>Ball cap group 27.19 MPa,the non-working side was Locator group 8.58 MPa>Ball cap group 7.52 MPa.When F3 was loaded to the left oblique direction,the working side of the equivalent stress on the neck of the implant was Locator group 32.94 MPa>Ball cap group 30.64 MPa,the non-working side was Locator group 7.05 MPa>Ball cap group 5.58 MPa.3.Tension and compression stress distribution of cortical bone around neck of implant The cortical bone around the neck of the implant on the working side mainly showed compressive stress distribution,the compressive stress was negative,and the negative value represented the downward direction.During vertical loading of F1,the left side of the bone compressive stress of the cortex around the neck of the implant was Locator group-9.57MPa>Ball cap group-6.71MPa,the right side was Locator group-10.14MPa and>Ball cap group-7.02MPa.When F2 was loaded to the right oblique direction,the working side of the compressive stress of bone in the cortex around the neck of the implant was Locator group-20.7MPa>Ball cap group-9.5 1MPa,the non-working side was Locator group-17.55MPa>Ball cap group-6.08MPa.When F3 was loaded to the left oblique direction,the working side of the compressive stress of bone in the cortex around the neck of the implant was Locator group-18.52MPa>Ball cap group-7.93MPa,the non-working side was Locator group-15.95MPa>Ball cap group-5.42MPa.The cortical bone around the neck of the implant on the non-working side mainly showed tensile stress distribution,the tensile stress was positive,which represented the upward direction.During vertical loading of F1,he left side of the bone tensile stress of the cortex around the neck of the implant was Locator group 3.84MPa>Ball cap group 2.51MPa,the right side was Locator group 4.5MPa>Ball cap group 2.97MPa.When F2 was loaded to the right oblique direction,the working side of the tensile stress of bone in the cortex around the neck of the implant was Locator group 6.09MPa>Ball cap group 4.21MPa,the non-working side was Locator group 8.02MPa>Ball cap group 6.1 MPa.When F3 was loaded to the left oblique direction,the working side of the tensile stress of bone in the cortex around the neck of the implant was Locator group 5.1MPa>Ball cap group 4.37MPa,the non-working side was Locator group 7.94MPa>Ball cap group 5.68MPa.Conclusions:1 Ball cap and Locator overdentures are more beneficial to the stress distribution of the alveolar ridge in the posterior area than the traditional complete dentures for the edentulous jaw with severe absorption.2 When the cortical bone in the neck and surrounding area of the implant was subjected to lateral force,the working side was more prone to stress concentration,suggesting that the working side was more prone to bone remodeling and resorption during oblique loading.3 The stress distribution of the implant neck of the Locator overdenture is different from that of the Ball cap overdenture.Under different loads,the equivalent stress of the implant neck under the working side of the Locator overdenture is greater than that of the Ball cap overdenture,which may be one of the reasons for mechanical complications of the implant.4 No matter the Locator overdenture or the Ball cap overdenture,under different loading conditions,the stress on the cortical bone around the neck of the implant was within the stress range conducive to cortical bone remodeling(1.3-170Mpa).Therefore,neither of the two repair methods would cause cortical bone resorption around the neck of the implant. |
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