The Distribution Of Stress In Functionally Graded Zirconia Root-analogue Implants:a 3D Finite Element Analysis

BackgroudsMarginal bone loss was observed in long-term clinical evaluation of implant dentures.The reason of that include patients’ oral hygiene,implant materails and the design of implants.The Zirconia implants are much harder than alveolar bone and two times harder than titanium.This considerable difference may generate high stresses at the bone-implant interface during load transfer,leading to implant failure.The use of functionally graded materials might induce lower and more uniform stresses in the supporting peri-implant bone.ObjectiveThe aim of this study was to investigate whether axial and radial functionally graded root analogue dental implants can optimize the stress distribution near the implant-bone interface in alveolar bone models under static loads by using finite element analysis(FEA).Materials and methodsThe three-dimensional structure of the nature tooth was got from one patient’s cone beam computerized tomography data and definded as the root-analogue implant.After smoothed the surface,the root-analogue implant model with alveolar bone was exported to ABAQUS software to be loaded and analysised.In radial functionally graded zirconina implant model,the implant was divided into 3,5 or 10 layers from the core to the surface of the implant in different model respectively.And the elastic of the implant core was a fixed value,220GPa,while that of the outermost layer was shifty values,namely 5GPa,13.7GPa,40GPa,110GPa and 220GPa,in different modles.In axial functionally graded zirconina implant model,the implant was divided into 3,5 or 10 layers from the cervical layer to the apical layer of the implant in different model respectively.The elastic of the peak layer’s elastic modulus was a fixed value,220GPa,while that of the lowest layer was shifty values,namely 5GPa,13.7GPa,40GPa,110GPa and 220GPa,in different modles.Each model mentioned above was loaded by four force respectively,namely lingual and horizontal 50N,medial ang horizontal 50N,vertical 100N and maximal and hybrid 118N.The distribution of stress,von Mises stress and strain in alveolar bone and implant were obvervational indexes to evaluate the impact of functionally graded zirconia in root-analogue implants.Results1.The maximal von Mises stress of alveolar bone located on the cervical region in all models.2.The maximal von Mises stresses of alveolar bone were similar in different layer root-analogue implant models,while those of implants in 3-layer root-analogue implants were higer than those in 5-layer and 10-layer root-analogue implants.3.As the maximal von Mises stress of alveolar bone,the mesial load model was the largest;the maximal load model was secondary largest;the lingual load model was sencondary smallest;and the vertical load model was the smallest.As the maximal strain of alveolar bone,the maximal load model was the largest;the lingual load model was secondary largest;the vertical load model was sencondary smallest;and the mesial load model was the smallest.4.In the radial functionally graded implant models,as the outer layer’s elastic modulus increased from 5GPa to 220GPa,the maximal von Mises stress of the cortical bone decreased from 110.OOMPa to 19.80MPa and the maximal strain of cortical bone decreased from 2.179*10-3 to 1.478*10-3.In all models,the maximum von Mises stress of the cancellous bone changed only slightly,from 2 to 5 MPa.And in the exponential variations model,the maximal von Mises stress of bone was the lowest.5.In the axial functionally graded implant models,as the lowest layer’s elastic modulus increased from 5GPa to 220GPa,the maximal von Mises stress of the cortical bone varied from 9.41MPa to 23.64MPa,and the maximum strain of the alveolar bone varied from 1.535*10-3～2.967*10-3.And in the logarithmic variations model,the maximal von Mises stress of bone was the lowest.Conclusion1.In root-analogue implant models,the maximal stress of alveolar bone aroud implant located on the cervical region.And horizontal loads would increase the stress of bone,which imply that the implant denture should avoid horizontal force.2.In the radial functionally graded implant models,as the outer layer’s elastic modulus increased,the maximal von Mises stress and strain of the cortical bone decreased.When the outer layer’s elastic modulus was larger than 40GPa,the alveolar bone would be in a stabilize state.And the exponential variations in elastic modulus could reduce stress of the cortical and cancellous bone.3.In the axial functionally graded implant models,as the lowest layer’s elastic modulus increased,the maximal von Mises stress and strain of the alveolar bone varied a little.And the logarithmic variations in elastic modulus could reduce stress of the cortical and cancellous bone.