The Biomechanical Study Of Micro-implant Anchorage In Orthodontical Treatment

Orthodontic treatment is the technique which orthodontists use acertain magnitude and direction force to achieve a given tooth movement,the modified growth of jaw bone in physiological reaction by orthodonticdevices, to achieve the orthodontic goal—treatment of occlusalanomalies. Therefore, it becomes the key to master the transfer oforthodontic force in the corresponding tooth, periodontal ligament andjaw bone, especially for the biomechanical effect of orthodontic forcehas the most important significance for clinical orthodontists choosethe proper force system. Except for choosing proper orthodontic appliance,orthodontists should choose a certain kind of organ or device to resistthe counterforce produced by orthodontic appliance. This organ or deviceis called anchorage. The micro-implant anchorage(MIA) system wasinvented recently among those anchorages, it is the special screw madein pure titanium with good bio-compatibility. The screws were inserted into jaw bone of different site to resist the counterforce produced byorthodontic appliances. The micro-implant system has lots of advantagessuch as small size, convenient practice and absolute anchorage effect,it lead up to a revolutionary influence to the traditional orthodontictreatment, most of orthodontists pay attention to this new anchoragesystem by reason of those advantages.No matter how careful design and practice before implanting themicro-implant anchorage, a certain ratio of failure of micro-implantanchorage is inevitable in orthodontic treatment and the failure ratioincreasing as load increasing. This phenomenon is related to the stressdistribution surrounding the micro-implant anchorage and thestress-strain distribution of the corresponding bone, which affectedby lots of factors such as the design of micro-implant shape andimplant-bone interface conditions etc.. Furthermore, there have thedifference between with or without the micro-implant anchorage systemin the orthodontic treatment. The whole force system was changed comparedwith the traditional force system, and we do not know this change clearlybecause of the lack of biomechanical demonstrations about themicro-implant anchorage system.There have lots of influence factors such as the complexity ofdentofacial structure, the oral functional movement and the applicationof orthodontic devices etc., it caused the biomechanical research of theorthodontic force system difficult. In recent years, the finite elementanalysis method developing quickly by the aid of computer application,it was introduced into the stomatological field and obtains the greatimprovement in the specifically biomechanical research. Apparently, it is the key to build the finite elemental analysis model for advancedresearch on the orthodontic force system with the micro-implant anchorage.At the same time, the finite elemental analysis model of the whole "MIA-orthodontic appliance-tooth-alveolar bone-jaw bone" have notbeen constructed, there still have several deficiency such as theslowness in model building, the lowness in model geometry and the lackof modularization etc.. Those unsolved issues cause the research of thisarticle.The first part of this research is to construct a three dimensionalfinite elemental analysis model of micro implant-bone interface. In thesecond part of this research, the stress-strain distribution of themicro-implant-bone interface was calculated based on consumptions ofdifferent micro implant-bone conditions. The third part of this researchis to construct the three dimensional finite elemental analysis modelof straight wire appliance, then add implant-bone interface model to thismodel to investigate the biomechanical effect of the micro implantorthodontic force system. The last part of this research is to investigatethe biomechanical effect of retraction of anterior upper teeth by using "MIA-orthodontic appliance-tooth-alveolar bone-jaw bone" forcesystem.PartⅠ.The fleetly and accurately construction of three-dimensionalfinite elemental model which including micro implant-bone interfaceObjective: To explore a new technique for constructing thethree-dimensional finite elemental model which including microimplant-bone interface by Materialise' s interactive medical imagecontrol system(Mimics 9.0).Methods: The maxilla with all teeth was scanned with Spiral CT and the images were transferred into the Mimics software to obtain thethree-dimensional images fleetly. The ABAQUS6.5 software was used to meshthis primary model and to establish the three-dimensional finiteelemental model with micro implant-bone interface at last.Results: The three-dimensional finite elemental model includingmicro implant-bone interface in high accuracy were constructed.Conclusion: The Mimics software is so available and effective inconstructing the three-dimensional finite elemental model. Furthermore,the geometrical analogy of this model was greatly improved by using theMimics software.PartⅡ. The compare of biomechanical effects in various microimplant-bone interfaces and among the different neck design of microimplant anchorage.Objective: To construct the finite element analysis model of variousmicro implant-bone interfaces and to analyze the stress distributionsof the implant-bone interfaces under the given orthodontic load. A newneck design of micro implant was developed based on the results of thebiomechanical effects of this model. The stress distribution of the newmicro implant was evaluated by ABAQUS software.Methods: Based on the above model, three bone-implant interfaceconditions were defined: the initial stability, full osseointegrationand fiberal integration. The stress distribution of the implant wasevaluated under 2N force.Results: The stress concentrated on the neck of micro implant in allmodels and the stress distribution of the full osseointegration interfacewas the lowest. The new design of the micro implant' s neck would decreasethe stress distribution.Conclusions: The micro implant acts as stable orthodontic anchoragein all three implant-bone interface situations. The new micro implant' sneck design is effective in decreasing the stress distribution. PartⅢ. The construction of three-dimensional finite elementalanalysis model of space closing mechanics by sliding method.Objective: To construct a three-dimensional finite elementalanalysis model of space closing mechanics by sliding method and toinvestigate the initial tooth displacement during space closing stagewith straight wire appliance.Methods: An adult skull was chose for CT scanning and the data wereimported into the Mimics software for three-dimensional reconstruction.The positions of the teeth were adjusted according the OrientalPread justed Appliance-KOSiKA(Opa-K:TOMY Company, Japan) system' s data.The wire and the brackets were established in the ABAQUS6.5 software andwere assembled to the teeth by Boolean operation.Results: The three-dimensional finite elemental analysis model ofspace closing mechanics by sliding method was constructed. Lingualtipping displacements were found with lateral and central incisors andthe compressive stress zones mainly appeared in the periodontal membraneof the lingual side of the incisors.Conclusions: The new technique to construct a three-dimensionalfinite elemental analysis model of space closing mechanics using slidingmethod is effective and feasible.PartⅣ. The influence of different MIA' s position and hook' s heightto the retraction of maxillary anterior tooth by sliding mechanicsObjective: Three-dimensional finite element method is an efficientway to investigate the force system of tooth movement. The purpose isto investigate the influence of MIA position and the hook height to theinitial tooth movement of maxillary anterior tooth by sliding mechanics.Methods: Three-dimensional finite elemental analysis models ofmaxillary dentition was constructed, it included the space for extractionof two first premolars, the periodontal membrane, alveolar bone, straightwire bracket and stainless steel wire (0.018×0.025inch).The initial teeth movements of maxillary anterior tooth retraction were evaluatedloaded with 1.5N force when the MIA position were 4mm and 8mm respectivelyand the retraction hook height was 1mm, 4mm, 7mm, 10mm respectively.Results: The lingual initial displacement of maxillary anteriortooth became more labial when the retraction hook height increased, atthe same time, the intrusion displacement was increased when the microimplant was inserted in a higher site of alveolar bone.Conclusions: The result provided an important reference for theselection of the position of the MIA and the height of retraction hook.