The Influence Of Different Ratios Of Implant Length To Loding Position: A Finite Element Study

With the rapid development of modern society,people's desire of beauty grows stronger day by day.As a branch of medicine,Orthodontics combines with Aesthetics,has been received more and more attention in recent years.Implant anchorage is crucial to orthodontic treatment.It could affect the treatment effects.Anchorage is a system to resist the force generated by the orthodontic treatment for dental malocclusions.Generally,anchorage includes tooth,dental arch,muscles of oral and cranial bones etc.The traditional methods to strengthen anchorage include using palatal bar, Nance arch,lingual arch facebow and improving the number of teeth et al.However,these methods have defects of not comfort and beauty,for example.In addition,these anchorages need the corporation of patients,so the anchorage losing could be caused and it's effects can not be guaranteed.Micro-implant anchorage produced recently is to resolve these problems;it recovers the limitations of traditional methods and becomes a hotspot of the researches at home and abroad.The success of micro-implant anchor lies in the stability in osseous tissue after implant.There have many researches about the stability of the implant.Three dimensional finite element is good at repeatability and avoids individual difference influencing the result in clinical trials and animal experiments. Therefore it becomes one of the important studies and favors by scholars.In the whole research,the basis of the experiment is to establish a 3-D model.The accuracy of model is vital to the ultimate result,thus the design ideal and method of molding is very important.More and more experiments care about how to establish the 3-D jaw bone model with implant.In the three dimensional finite element,the implant stability is mainly to observe the stress and displacement in the implant-bone interface.A lot of factors can influence the stress and displacement in the implant-bone interface.A large number of researches have been made about the diameter,shape,taper, surface coating of implant and also the magnitude,direction, position of loading,insert site,thickness of cortical bone,the quantity and quality of bone,et al.In these researches,studies achieved many valuable research results.Because of the difference of insert site,the thickness of bone and mucosa may be having considerable difference.So the loading position and implant length we selected often change,the ratio between them will change too.The loading position is not have unified standard for different implant length.Some people think if the ratio is improper will cause the excessive displacement of the implant,bone damage and resorption.Finally it maybe brings about implant failure.It has not been reported currently that what the change ratio of implant length to loading position will influence the stress distribution in implant-bone interface. Moreover,it is not in agreement that implant length how to influence the stress distribution in implant-bone interface.Objective:To analysis the influence of ratios of implant length to loading position on the stress distribution in implant-bone interface for providing the theory basis to select an appropriate mini-implant in clinical.Method:Used spiral CT scan,Dicom3.0 and Mimics10.01 to input the tomoscan data of normal mandible to computer.To build three-dimensional finite element models of reconstructed mandible with mini-implant anchor.The lengths of the screw were 6mm,8mm,10mm and 12mm respectively.A force loading of 200g was applied mesio-distally on these implants and the heights of loading positions were 2mm,4mm,and 6mm to the implant,respectively.Observing in different situation of the ratios of implant lengths to loading positions,how the stress and displacement distribute in implant-bone interface.Result:1 Used spiral CT scan,Dicom3.0 and Mimics10.01 to build three-dimensional finite element models of reconstructed mandible with mini-implant anchor.These models truthfully and accurately imitated the relation after implant-bone interface, better biological and geometrical similarity,which lay the solid foundation for acquiring closer actual results. 2 The change of the height of loading position influenced the Von-Mises stress and displacement distribution in implant-bone interface obviously.The peak value of the stress and displacement increased as the increase of the heights of loading positions.When the heights of loading position were 2mm,4mm,6mm respectively,the stress at the neck level of implant-bone interface were 6.582GPa,12.360GPa,18.152GPa respectively.And the displacements were 0.736μm,0.786μm, 0.83μm respectively.But the increase of stress and displacement were not linear relation.When the height was increasing,the stress was more inhomogeneous.And it can cause stress concentration on the neck,implant deformation, implant breaking off and falling out.3 The change was not obviously,which the implant length inside bone influenced the Von-Mises stress distribution in implant-bone interface.When the lengths were 6.8mm,8.8mm, 10.8mm,12.8mm respectively,the peak value of stress on the neck,and the peak value were 6.582GPa,12.360GPa,and 18.152GPa respectively.The displacements were 0.887μm, 0.837μm,0.809μm,0.890μm respectively.The change of stress influenced by the increasing of the length is not obviously.But the change of the displacement is more obviously.4 The change of ratios of implant length inside bone to heights of loading position influenced the Von-Mises stress and displacement in implant-bone interface.With the increasing of ratio,the curves revealed a general trend of decrease. Conclusion:1 The methods that using Dicom data to build model directly could imitated the loading conditions between bone and implant actually.2 The change of the height of loading position influenced the Von-Mises stress and displacement distribution in implant-bone interface obviously.Thus,in clinical treatment,the height of loading positions should be reduced in order to decrease the Von-Mises stress and displacement in implant-bone interface.3 The change of the implant length inside bone influenced the Von-Mises stress distribution obviously;however,the change of displacement distribution is not obviously.If the clinical condition is allowed,we can improve the implant length properly.But it is not the longer the better.4 The change of ratio,between implant length inside bone and heights of loading position,influenced the Von-Mises stress and displacement in implant-bone interface.A general trend is that with the ratio increasing,the Von-Mises stress distribution is more uniform.So we should try to increase the implant length and decrease the height of the loading position.