Biomechanical Effect And Rule Of Mini-implant With Single Or Multiple Loading

Objective:During clinical orthodontics, anchorage is usually the critical factors that affecting the therapeutic efficacy which would cause mini-implant failure when the orthodontic anchor is inappropriate.Titanium mini-implant has been utilized as an anchor during orthodontic treatment recently These appliances designed for orthodontic anchorage can be placed in any place in the alveolar bone, and the surgical procedure is petty enough for evasion of inflammation because of the small size of the implant.However, many investigations have confirmed that the implant body has high stability, some clinicians still find a loosening of the mini-screws during treatment. According to a report the success rate of the mini-implant is about 89%,these greatly influences the widely use in clinical practice.The factors that influence the stability of the mini-implant including biological and biomenchanical stability.Development of material science greatly improve the biological stability of mini-implant.the biomenchanical stability of mini-implant is taken seriously now.researchers have done a lot of study on prosthesis implant,but the mini-implant used for orthodontic is different.No matter in inserting point or loading mode. some researchers have been investigated the inserting anglea and the loading directions of the mini-implant,they all have a marked influence on the distribution of implant-bone stress.However,the loading mode of the implant is versatile and complex in clinical with single direction or composite directions,it related to the objective of the treat.there are no report about stress distribution surrounding bone-implant with different loading mode.Three dimensional finite element method by establishing accurate dental system model,simulate the stress and displacement of implant and surrounding tissues under real loading,and less influenced by other factors. It has proved to be an effective method in recent years.Experiments in this study is using three dimensional finite element method. The aim of the study was to investigate the stress and displacement around an implant in response to different directions of force application when insert the mini-implant with two insertion angle.In order to select a better way for the stability of mini-implant.Methods:1 ExperimentComputer:Dell precision (Intel(R) Core(TM) i7-4800MQ CPU@2.70GHz:32G memory, win7,64bit operating system)Packages:Mimics, Catia V5, Hyperworks 12.0, Abaqus6.13, excel,screen shot tool.2 The model of mini-implant and jaw2.1 Establishment of modelThe range of mini-implant diameters is restricted because the mini-implants designed as orthodontic anchors must be able to be placed in any area of alveolar bone. According to the size of clinical use,we establish a model of implant with a diameter of 1.6mm, thread height is 0.3mm,the pitch of the screw is 0.5mm and the blade-like thread apex angle of 60 degrees.The mini-implant used in this research is made of pure titanium.The bone element was designed to be a 20mm in length,20mm in width and 10mm in height(surface for cortical bone,inner for cancellous bone.these cortical bone thickness is 1mm and the thickness of the cancellous bone is 9mm),which is sufficiently large to assess the stresses and strains surrounding the mini-implant. So the length of the mini-implant inside the bone is 8mm.2.2 Assemble the implant-bone modelIn the geometric center of the surface of bone model as the insertion point of the mini-implant. Setting X axis parallel the side of the bone edges and through the insert point. Setting Y axis parallel the other side of the bone edges.The Z axis is perpendicular to the bone surface.The two insertion angles are vertical implantation and diagonal with a 45 degree angle to the positive direction of Y axis respectively.2.3 The size, mode and direction of the loadThe traction force was fixed at 2N,which is the approximate orthodontic force applied to a mini-implant in clinical practice.We set the size of the load in this study is 2N or 2(?)2N.the point of loading were on the neck of mini-implant.The loading mode is single loading or double loading simultaneously, All of the loading direction is parallel to the X-Y plane.2.4 Experiment grouping designSet the X axis is in the same direction when loading direction is 0 degree,experimental groups are as follows:Mini-implants inserted perpendicular to the X-Y planeLoadⅠ-A Applied 2N of orthodontic force with the X axis positive direction at 0 degreeLoadl-AB Applied 2N of orthodontic force with the X axis positive direction at 0 degree and 180 degree at the same timeLoadⅠ-C Applied 2(?)2N of orthodontic force with the X axis positive direction at 90 degreeLoadⅠ-DE Applied 2N of orthodontic force with the X axis positive direction at 45 degree and 135 degree at the same timeLoadⅠ-FG Applied 2N of orthodontic force with the X axis positive direction at 25 degree and 155 degree at the same timeMini-implant inserted diagonal with a 45 degree angle to the positive direction of Y axisLoadⅡ-A Applied 2N of orthodontic force with the X axis positive direction at 0 degreeLoadⅡ-AB Applied 2N of orthodontic force with the X axis positive direction at 0 degree and 180 degree at the same timeLoadⅡ-C1 Applied 2N of orthodontic force with the X axis positive direction at 90 degree and Y axis positive direction at 0 degreeLoadⅡ-C2 Applied 2V2N of orthodontic force with the X axis positive direction at 90 degree and Y axis positive direction at 0 degreeLoadⅡ-D Applied 2N of orthodontic force with the X axis positive direction at 45 degreeLoadⅡ-DE Applied 2N of orthodontic force with the X axis positive direction at 45 degree and 135 degree at the same timeLoadⅡ-F Applied 2N of orthodontic force with the X axis positive direction at 25degreeLoadⅡ-FG Applied 2N of orthodontic force with the X axis positive direction at 25 degree and 155 degree at the same timeLoadⅡ-H Applied 2N of orthodontic force with the implant angle at 0 degree3 Materials3.1 Entity modelingTo use of the electronic computer technology,three-dimensional model of the jaw and implant is established.Fomation the assembly of vertical and inclined at 45 degree.The implant,cortical bone and cancellous bone were assumed to be continuous,homogeneous,isotropic(directionally independent) and linearly elastic.The material deformation is small.3.2 MeshingImport the three-dimensional model into Hypermesh model of the finite element modeling software Hyperwork 12.0,and the refine the model grids.3.3 Parts connection andImported the mesh finite element model into the Abaqus 6.13,according to the different parts of the material properties,established model and give the part material properties.The coefficient of friction between the implant and bone μ=0.3.3.4 The observation indexes Using Hyperworks 13.0 Hyperview module to view result Collecting Von-Mises stress value,compressive stress,tensile stress and displacement value,analysis the stress and displacement distribution and the strain Kgularity.Results:1 Establish the implant-bone models of different loading directions withtwo inserting angles.The biological similarity of the model is well.2 We build two models,one is with vertical implantation,the other is with tilt implantation.Both of them were under five loading directions.The Von-Mises stress and the displacement were observed at the sharp bone margin which in that direction(red area). It might show that the peak value of stress and displacement are mainly concentrated in the cortical bone.When transition from cortical bone to cancellous bone,the value of Von-Mises stress and displacement showed a decreasing trend.3 When the mini-implant inserted vertical,the Von-Mises peak value ranged from 8.72 to 0.7186megal pascal(MPa),the displacement peak value ranged from 5.525 to 2.016μm.The maximum value is when loading at 45 degree and 135 degree at the same time,secondly is loading with single direction Load-A,the next is Load-FG,and the minimum value is when loading at 0 degree and 180 degree at the same time.Load-C set as the control group to Load-A,loading with 2V2N which calculated according to the laws of mechanics.it is worth noticing that compare the value between stress and displacement’s nearly the same of Load-C and Load-DE.4 When the mini-implant inserted diagonal with a 45 degree angle,the Von-Mises peak value ranged from 7.293 to 0.2612megal pascal(MPa),Load-DE still the highest and Load-AB the lowest also.However, there is no significant difference between Load-A,Load-C and Load-FG.5 When loading in the same direction with vertical group and tilt group,the latter is less than the former of Von-Mises stress.Tilt insert is common in clinical practice because of the narrow distance between two adjacent tooth in the planting area.it can be used as a reference in clinical practice.However the value of displacement in Load-FG in tilt insertion is less than in vertical insertion.Conclusions:1 With composite load,the intersection angle by two loading direction with the best stability to the mini-implant,with the less stress and displacement distribution around the mini-implant;2 When the mini-implant inserted vertical,the resultant of the composite loading force in line with the parallelogram principle,the less of angle of the composite loading the resultant of force is large,the stress of implant-bone is large.The approximate opposite of the loading direction,the stress is less.3 When the mini-implant inserted with 45 degree angle,it may expose a difference insertion torque with a difference loading directions.the resultant of the composite loading force with no effect with the parallelogram principle.However,the mini-implant inserted tilt has a more reasonable distribution of stress than inserted vertical when single loading or composite loading that because the increase of the decrease of the insertion torque and the contact area of the implant-bone,it has a clinical significance.