Effect Of Porous Microstructure On The Biomechanical Characteristics Of Root Analogue Implant

The design of custom-made root analogue implants(RAI)mimicked natural tooth.However,it may lead to stress shielding of the surrounding bone,and it's hard for RAI to obtain primary stability.So porous structure was applied to the surface of custom-made RAI in this study to solve these problems.The purpose of this study was to evaluate the effect of porous microstructure on the biomechanical characteristics of custom-made RAI.The stress distribution on the bone surrounding RAI was evaluated via a 3-D finite element analysis in this study.First of all,a simplified three-dimension geometry of anterior maxilla was constructed.Then based on the extracted STL data of right maxillary central incisor,5 RAI models with different surfaces were constructed: A.smooth surface,B.pit surface,C.bulbs surface,D.threaded surface,E.porous surface.And a conventional implant model was also constructed to serve as control group.A static load of 100 N in the multivectoral direction from palate side to the labial side was applied to the crown.And the applied force wasat a 45°angle to the long axis of implant.The result of this 3-D finite element analysis indicates that in porous surface RAI model,mean von Mises stress of bone was higher than other models,and von Mises stress was lower than conventional implant.Besides,the percent of elements of which equivalent elastic strain values were ranged from 100 microstrain to 3000 microstrain was significantly higher in porous surface RAI group than other groups.The micromotion in the implant-bone interface was ranged from 3.5?m to 6.2?m in all the groups.Then bone formation of porous Ti6Al4 V custom-made RAIs was assessed via a beagle dog experiment and a clinical study.Porous custom-made RAIs were fabricated by CBCT and SLM technology.In the vivo experiment of beagle dog,fabricated porous custom-made RAIs and conventional implants clinically used were implanted into the extraction socket in the mandible.After a no-load healing period of 8weeks,the beagle dog was sacrificed.Clinical,radiographic and histological evaluation suggested that porous custom-made RAIs had good biocompatibility,and the porous structure in the surface of custom-made RAIs can promote the growth of new bone.Besides,all the implants could achieve good osseointegration.In the clinical study,after the extraction of right mandibular first molar,fabricated porous custom-made RAI was implanted into the extraction socket immediately.Then a temporary crown was made to protect the soft and bone tissuesurrounding implant.After a healing period of 3 months,the permanent crown was made and attached to the custom-made RAI.The X-rays taken at 3 months after surgery indicated that porous custom-made RAI could achieve osseointegration,and there were no obvious surrounding bone resorption.In the end,the following conclusions can be drawn: 1.The bone tissue surrounding porous custom-made RAI subjected to more uniform stress and the phenomenon of stress concentration reduced,which is conducive to bone tissue growth.Moreover,“stress shielding” effect was also reduced.2.The porous structure in the surface of custom-made RAI can induce surrounding bone grow into pores better and faster.3.Custom-made RAI could achieve osseointegration.