Implant-supported Removable Partial Overdenture Restore Different Bone Types’ Kennedy ClassⅠdentition Defect: A Biomechanical Analysis

Objective: Three-dimensional finite element stress analysis was used to explore the stress relationship between the attachment(Locator attachments,Magfit magnetic attachments)of implant support removable partial denture which used to restore mandibula kennedy class Ⅰdentition defect and different bone quality,in order to match more suitable attachments for different bone types.Methods: A finite element model of mandibular first premolar to second molar loss was established.Eight models were constructed according to bone type and attachment type: L-Ⅰ,L-Ⅱ,L-Ⅲ,L-Ⅳ,M-Ⅰ,M-Ⅱ,M-Ⅲ and M-Ⅳ.The model was meshed,the material properties and the boundary conditions were set,and the contact conditions were defined.The buccal bevel,buccal lingual bevel and central fossa of the mandibular artificial premolar and molar were selected as the activation points.The activation directions were buccal 45 °(B),lingual 45 °(L)and vertical(V),respectively.The stress distribution of removable partial denture,implant,jaw,natural tooth and other components was analyzed,and the stress distribution cloud diagram,maximum von Mises stress value,maximum shear stress value and total displacement value were obtained.Results: 1.Three-dimensional finite element models of tooth tissue,periodontal tissue,mucoperiosteum,implant,attachment,removable partial denture,cortical bone and cancellous bone were established.2.The maximum equivalent stress value and maximum shear stress value of mandibular cortical bone and implant-bone interface gradually increase with the loosening of jaw bone density,while the maximum equivalent stress value and maximum shear stress value of cancellous bone decrease with the decrease of bone density,all of which were not affected by the type of attachment and load direction.When subjected to vertical forces,the maximum equivalent stress values of cortical bone,implant-bone interface,and cancellous bone were greater in the Magfit attachment group than in the Locator attachment group in each bone quality,but the opposite was true in the non-vertical direction.3.When the denture is subjected to force,the stress of the metal stent of the denture is mainly concentrated in metal weak areas such as the tongue bar and snap ring of the denture.In the two attachment types,there was no significant difference in the maximum equivalent stress value and shear stress value of the metal stent between different bone types regardless of the loading direction of the force.However,in the same bone type,the difference between the two attachments was large: the Magfit attachment group received the largest shear stress value in its metal weak area when it was not vertically stressed,about 3.2 times that of the Locator attachment group;while the denture received the smallest shear stress value when it was vertically stressed,about 7% of its own non-vertically stressed,and 66% of the Locator attachment group.The maximum shear stress value of the weak area of the metal stent under different loading modes of the Locator attachment group was not significantly different,and its ratio was B: L: V = 1.46:1.33:1.4.There was no significant difference in free-end extensive denture displacement,maximum equivalent stress value of abutment periodontal ligament,total mucoperiosteal displacement and maximum equivalent stress value between different bone types of the same attachment.However,in the same bone type,there were differences between different attachments: during vertical loading,free-end extensive denture displacement,maximum equivalent stress of abutment periodontal ligament,total mucoperiosteal displacement,and maximum equivalent stress in the Magfit attachment denture group were less than those in the Locator attachment denture group,as opposed to non-vertical loading.Conclusion: Based on the results of this experimental study,it can be seen that: 1.The mechanical conduction effect of Locator attachment and Magfit magnetic attachment is different between different bone types.This difference is mainly reflected in the maximum equivalent stress value,shear stress value of jaw cortical bone and implant-bone interface which increase with osteoporosis,as well the stress value of jaw cancellous bone decreases with osteoporosis of the same attachment type.2.When subjected to non-vertical force,the adverse stress concentration formed by the denture repaired with Magfit attachment in metal weak areas such as tongue bar and snap ring was significantly greater than that of the denture repaired with Locator attachment.3.Compared with Locator attachment,Magfit magnetic attachment protects the implant from lateral forces and is more suitable for implant overdentures of osteoporotic bone types.