| Objective: In this study,Finite Elements Analysis(FEA)was used to analyze the stress distribution of mandibular edentulous fixed prostheses under dynamic loading,and to observe the effect of different number of implants and distribution methods on the stress values and stress distribution patterns during the chewing cycle.From a biomechanical point of view,it provides theoretical support for the clinical selection of mandibular edentulous implant fixed prosthetic solutions.Methods: A Cone Beam Computed Tomography(CBCT)scan taken in March 2021 was selected,and saved in DICOM format.The 3D solid model of the mandible and implant prosthesis(implant,abutment and crown)was constructed using Mimics 21.0,Geomagic Wrap 2017 and Solid Works 2017 software.Thirty-five in vitro models of 4,5 and 6 implants were constructed with different distributions of the implants,while keeping the distribution as uniform as possible and restoring to the first mandibular molar.The experimental models of each group were imported into Ansys Workbench2021R1 software,meshed,and experimental assumptions,boundary conditions and parameters were set.A dynamic load of 200 N force simulating a chewing cycle of0.875 s was applied to the mandibular first and second premolar teeth,and the first molar implant joint crown.The Von Mises equivalent forces for each group of implants,abutments,surrounding bone tissue and crowns were selected as indicators for the finite element analysis.Results: 1.A total of 35 groups of 3D finite element models of implant crown repair and bone supporting tissue with 4、5 and 6 implants in different distribution were successfully constructed.The established finite element model has fine mesh division,good geometric similarity,and can meet the needs of dynamic loading simulation.2.Under dynamic loading,the implant stress of all models was mainly concentrated at the joint of implant and abutment.In the farthest part,the implant stress was the most concentrated,which was mainly concentrated at the buccal side where the implant and abutment were connected.The buccal stress concentration became more obvious with the change of stage.The peak stress of bone tissue in all models appeared at the junction of cervical margin and cortical bone.Under vertical loading,the crown stress mainly concentrated on the loading site,while under oblique loading,the crown stress mainly concentrated on the adjacent site of the posterior tooth crown.3.In the dynamic period,the 35 groups of implants and surrounding bone tissue reached the peak of dynamic loading period when the tongue and tongue loading was carried out,in which the tongue and tongue loading > the tongue and tongue loading > the vertical loading,the tongue and tongue loading increased about 1.7-4.7times compared with the vertical loading,and about 1.2-2.3 times compared with the cheek and tongue loading.Conclusion: 1.During the chewing cycle,the influence of oblique loading on the stress of implant,surrounding bone tissue and dental crown was greater than that of vertical loading,and the lingual loading was greater than that of buccal loading.Therefore,the design of the prosthesis can be adjusted according to the stress characteristics of each stage.The lateral force can be minimized by reducing the slope of the buccal tip and eliminating the interference of the lateral occlusion.2.In the design of implant restoration scheme,the distribution of implants should follow the principle of uniformity and dispersion.When mandibular bone volume was sufficient,6 implants were superior to 4 and 5 implants in both peripheral bone tissue and implant stress distribution.3.The position of the implant is an important factor influencing the bone stress around the fixed denture,where the most anterior implant should be placed as far as possible in the position of the lateral incisors or cusps. |
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