Three-dimensional Finite Element Analysis Of Edentulous Mandibular Four-implant Overdenture

Objective: To analyze the influence of two connection ways via ball cap and Locator on stress distribution of mandible and implants and the influence of bone quality on stress distribution of edentulous mandibular four-implant-supported overdenture via Locator attachment by establishing finite element models of edentulous mandibular four-implant-supported overdenture.Methods: The cone beam computerized tomography(CBCT)data of edentulous mandibular patient were collected,and finite element models of implant-supported overdenture via ball cap and Locator attachments and edentulous mandibular four-implant-supported overdenture via Locator attachment from four bone type were established respectively by Mimics software,Gomagic Studio software and Solid Works software,all models were loaded with the following two forces:F1,the axial force of the 120 N on the right lower molar(parallel to the long axis of the implant);F2,the lateral force of the 120 N on the right lower molar(30 degrees in the linguobuccal direction),,stress distribution on the mandible,and implants under different loading directions and the influence of bone quality on stress distribution of the cortical bone,the cancellous bone and implants were analyzed combined with ANSYS software.Results:(1)Under different loading directions,stress concentration was found on the cortical bone of the neck of implants of the loading side and lower margin of mandible median lingual region.(2)Stress concentration was mainly found on the neck of implants the loading side.(3)Stress in the stress concentration region of the Locator connection was lower than that of ball cap connection under the same loading direction.(4)The maximum von-Mises stresses of the peri-implant cortical bone region on the loading side increased progressively from type 1 bone to type 4 bone in the four types of bone models under the same loading direction.(5)The maximum von-Mises stresses of the peri-implant cancellous bone region on the loading side decreased progressively from type 1 bone to type 4 bone in the four types of bone models under the same loading direction.(6)The maximum von-Mises stresses of the neck of implants on the loading side increased progressively from type 1 bone to type 4 bone in the four types of bone models under the same loading direction.Conclusion:(1)The area on the peri-implant cortical bone and on the neck of implants were stress concentration area for four-implant-supported overdenture.(2)The von-Mises stress of overdenture by Locator connection is more dispersed than that of ball cap connection;overdenture via Locator connection is more favorable to the physical health of alveolar bone and long-term persistence of implants.(3)The maximum von-Mises stresses of the peri-implant cortical bone region and the neck of implants increased progressively from type 1 bone to type 4 bone,which increased the risk of marginal bone resorption;it can infers the compact bones(types 1 and 2 bone)are the most suitable bone type for edentulous mandibular implant-supported overdenture,and poor bone quality(type 4 bone)may increase the risk of biomechanical failure of implants.