The Finite Element Analysis Of Platform Switching With Different Mismatch Sizes And Insertion Depth On Stress Distribution In Peri-implant Bone

With the development of the technology,the long term stability and aesthetic effect of implants have been paid more attention.The preservation of the peri-implant bone is a key factor affecting the aesthetic effect of the implant.With the application of platform switching design,a large number of clinical trials confirmed that the absorption of bone tissue around the implant was significantly reduced.It had been suggested that the extent of implant-abutment mismatch size had a positive effect on cortical bone,but it is still controversy whether increasing the horizontal distance from adjacent bone to implant-abutment interface may decrease the marginal bone loss.Some authors proposed that the relative position of the implant-abutment interface and the alveolar bone may affect the bone resorption around the implant,but the mechanics and biologic factors of the insertion depth that affect the bone absorptionstill need further study.With the use of finite element analysis,this study aims to evaluate the effect of different abutment mismatch sizes and insertion depth of platform switching implants from the prospective of biomechanics.Part Ⅰ The stress distribution of platform switching with different mismatch sizes on marginal bone tissue:the finite element analysisObjective:To analyze the influence of platform switching implant with different implant-abutment mismatch sizes on the stress distribution in peri-implant bone.Methods:The left mandibular molar model was obtained from the CBCT scanning of an edentulous mandible.Based on the Ankylos implant system(Ankylos C/X 4.5×11mm and 3.5×11mm)and Nobel implant system(4.3×11.5mm),eleven 3D models was simulated.In the group of 4.5×11mm implant system,the abutments were designed with diameters of 4.0mm(PS-0.5),3.5mm(PS-1.0),3.0mm(PS-1.5),2.5mm(PS-2.0),2.0mm(PS-2.5)and 4.5mm(PM)respectively.In the group of 3.5×11 mm implant system,the abutments were designed with diameters of 3.0mm(PS-0.5),2.5min(PS 1.0),2.0mm(PS-1.5)and 3.5mm(PM).In the group of 4.3×11.5mm implant system,the diameter of the abutment was 4.3mm(PM).A vertical and an oblique load of 100N were applied on the occlusal surface of the abutment to analyze the stress distribution on peri-implant bone.Results:Under two different load conditions,the implant group with diameter of 4.5mm has a lower maximum von Mises stress in the peri-implant bone when comparing with the implant group with diameter of 3.5mm.Compared with the platform-matched implant,the group of platform switching implant has a lower maximum von Mises stress in the peri-implant bone.With the decrease of abutment size,the maximum von Mises in cortical bone were reduced.Nevertheless the trend of stress concentration in periimplant bone was observed again when the size of abutment declined too much.Conclusions:The amplitude of horizontal mismatch may have a positive effect on the reduction of the stress concentration on peri-implant bone.However there was still a trend of stress concentration when excessive reducing the diameter of the abutment to increas mismatch size.Part Ⅱ The finite element analysis of the effect of platform switching on the marginal bone tissue with different insertion depthObjective:To evaluate the effect of insertion depth of the platform switching implant on the peri-implant bone tissue.Methods:The finite element models of the mandibular molars,the Ankylos implant system(4.5×11mm)and the abutment with the diameter of 2.5mm,were assembled with different insertion depth(epicrestal,subcrestalb 1mm and subcrestal 2mm).The changes of the stress distribution in the marginal bone tissue were analyzed with the load ofvertical 100N and 45° 100N respectively.Results:Under these load conditions,the stress on the cortical bone was mainly concentrated around the neck of implant platform.With the implant abutment interface moved down,the stress concentration area shifted downward from the top ofthe alveolar crest.With different loading,the platform switching implant with subcrestal(-lmm)positions had a lower maximum von Mises in cortical bone.Conclusions:The increase in implantation depth of the platform-switched implant is beneficial to reduce the stress on the alveolar bone,however,when increasing the insertion depth,the cortical bone around the platform of implant is needed as much as possible.