| Objective: Malocclusion refers to the abnormal arrangement of the teeth,inharmonious relationship between the dental arch and jaw and betweenDental and craniofacial in the process of growth and development of childrendue to various causes, which not only affect the appearance of patients but alsoaffect chewing. Tooth movement is completed by the orthodontic force.In the orthodontic treatment, any force applied to the teeth must producean equal but opposite force. So we call the device which could support thetooth movement caused by counterforce "anchorage". Anchorage usuallyrelies on one tooth or a group of teeth, but it cannot meet the demand ofanchorage in orthodontic treatment, so as to limit the treatment and affect thetherapeutic result. So devices that can reinforce the anchorage are needed,such as headgears, Nance arch, TPA and so on. But patients often do not fit towear them as they are big, uncomfortable or affect Influence theirpronunciation and appearance, consequently the therapeutic effect isundesirable.Micro-implant anchorage as a new effective orthodontic anchorage formhas the advantages of small volume, easy surgical operation, small trauma andsound patient compliance. It is widely used in the treatment of open occlusion,retraction of anterior teeth, depression of anterior teeth and pushing back ofmolars and achieved good clinical results. The stability of the implant is thebasis of functioning of implant anchorage. The implant-bone interface stressof the uniform distribution as an important index of implant stability isconcerned by scholars.It is researched that the implant-bone interface stress is found concentratedon the cortical area, which not only affect the uniform distribution on theimplant-bone interface, but also may cause micro damage because of localcompression ischemia around the implant, influence the healing ofimplant-bone interface. How to decrease the peak stress of the cortical bone effectively? Some attempt to change the configuration of the neck of theimplant to reduce implant-bone interface peak stress, then it is found thatincreasing the diameter of the implant’s neck is in favour of decreasing thedistribution on the cortical bone.This experiment is aimed to ensure the effect the changing of height andtaper of the implant’s neck put on itself.In this study, Ansys workbench13.0software was used to explore that inthe cortical bone which is2mm thick, implant-bone interface stressdistribution changes in the of the changes along with height and taper of theneck changing within a certain range. It provides a theoretical basis forimproving the implant neck configuration, improving the stability of theimplant and the production and clinical application of the implant.Materials and Methods：Experimental equipment:Hardware: PC,(Hewlett-Packard), spiral CT.Software: ANSYS workbench13.0Ifinite element analysis software,MIMICS10.01(Materialise company).Material: titanium implants1.1implant design:The geometry of micro-implant with reference to the commonly usedclinical size, bone segment length of8mm, diameter of3.5mm, thread heightof0.1mm, the blade-like thread apex angle of60degrees, the pitch0.5mm.The neck of implant bone section optimization design: neck diameter of1.5mm, and the variation range of the micro-implant neck taper (T) of0°~45°Neck height (H) of0~3mm ranges, the bone segment of the remainingportion (8~5mm). The design of1.2Mandibular model design:The dimensions of the jaw model were from the longitudinal section of oneside of the mandibular CT image between the second premolar and the firstmolar of an adult male volunteer. The mandibular CT image was obtained forestablishing jaw FEA models. The longitudinal section of mandibular wassimplified for hexagon. The surface of jaw models was cortical bone, and the rest for cancellous bone. The hexagonal section size were the upper surfacewidth of10.89mm, the middle width of18.2mm, the lower surface widthof11.94mm and height of39mm.1.3Assembled micro implant-mandible entity modelSimulating retraction of anterior teeth by loading2N force on the implant inthe direcion of30°to occlusion plane.2Material2.1Material PropertiesAssuming the implant, cortical and cancellous bone are continuous,homogeneous, isotropic, linear elastic material whose material deformation iselastic small deformation. Implant and bone interface is completelyosseointegration without any displacement.2.2MeshingAccording to the shape of the implant, the model is established by PCtechnology. Ansys workbench13.0software was used with model meshing.Dimensional finite element model of maxillary and implant is meshedautomatically by computer, so as to form a the implants three-dimensionalfinite element model.3Loads and constraintsThe micro-implant is loaded to simulate the retraction of anterior teeth inthe orthodontic treatment. The force is loaded in the neck of implant, which is2N and in the direction of30o to mesial occlusion plane.4Analysis methods and indicators4.1Input variables setTaper (T) of the implant’s neck is set in the present experiment (bone innersection) changes in the range of0°~45°, the neck height (bone inner section)h0~3mm, so that the results of this study can be observed continuously thatinput variables have influence on the output variables. Analyse the interactionof taper and height by bivariate response to surface observation.4.2Output variables setMaximum Von-Mises Stress of cortical and cancellous bone and peak displacement as output variable to be mechanical evaluated by differentdesigns. Sensitivity analysis of output variables.to input variables is conducedat the same time.Result:1Establishing the initial three-dimensional finite element model of the microimplant-mandible of the height of1.5mm, taper22.5°,median value,2Implant-bone interface stress distribution: the peak stress and displacementpeak cortical bone implant in the establishment of continuous change implantheight and taper model is far greater than the peak stress and displacement ofcancellous bone, indicating that the implant stress is mainly concentrated atthe neck of the implant.3The taper of the neck of implant’s influence on the stress and strain: Whenthe height is median value,1.5mm, taper changes from45°to90°, the stress(0.98~5.30Mpa) increases significantly as the taper increases. It is shownthat the neck is conical is more beneficial to reduce peak stress on the neck ofthe implant than cylindrical.4The height of smooth cylindrical part’s influence on the stress and strain:When the taper is median22.5°, as the height increases, the stress (0.47~5.70Mpa) in the cortical bone significantly decreases.5Sensitivity analysis showed that the implant height is more sensitive than thetaper to the the stress and displacement in the implant-bone interface.6Software analysis is that when the implant’s taper is more than10°andheight is close to the thickniss of cortical bone, the peak stress anddisplacement in the implant-bone interface is minimum.Conclusions:1The implant stress is mainly focused on the cortical bone area.2The implant without screws is more conductive to stress distribution ofimplant-bone inter face than with screws.3The neck is conical is more beneficial to reduce peak stress on the neck ofthe implant than cylindrical.4The height of smooth cylindrical part’s is more beneficial to reduce peak stress on the neck of the implant than cylindrical.5The height of the implant’s impact is more remarkable than the taper.6The height and taper interact with stress distribution.7The change of micro-implant neck configuration has some influence on theimplant-bone interface stress and displacement. It is more favorable that theneck of the implant’ taper is more than10°and height less than the thicknessof cortical bone for the uniform distribution of stress of the implant in theranges of taper of45°~90°and the height of0~3m... |
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