Stress Analysis Of Composite Archwire(CoAW) Applied In Extraction Cases

To accelerate orthodontic tooth movement and reduce theorthodontic treatment period are the main exploring subjects ofclinical orthodontic research . There are two research aspects in thisfield, one is focusing on how to accelerate bone remodeling inducedby orthodontic force,and the other is focusing on how to develop theadvanced and efficient orthodontic appliance, that is also called theresearch about the orthodontic materials . The orthodontic archwireplay the key role of developing the orthodontic materials. Up to now,the TiNi shape-memory alloy archwire(TiNiSMA) and StainlessSteel archwire (SS) materials are employed in clinical orthodonticsnot only in china but also in abroad. The benefit of TiNiSMAarchwire is its super-elasticity which could produce the physio-logical orthodontic force to move the tooth toward the right waywhen it was placed in the slots. But the rigidity of TiNiSMAarchwire is too small which could result in the anchorage loss ndget the undesirable tooth movement in some circumstances. Onthe contrary, the rigidity of SS is too high, which could produceenough anchorage for posterior teeth ,but it is hard to place the SSin the slots in the initial stage of orthodontic treatment because of itslow elasticity, therefore sequence of archwire application should befrom the thinner to the thicker and from the softer and the harder . Itis generally accepted in orthodontic clinic that we must useTiNiSMA firstly ,then use SS secondly, thus the treatment durationis prolonged. In most orthodontic cases, we need the less rigidityarchwire match to anterior teeth for its accessibility for being placedin the slots and need the more rigid archwire match to posteriorteeth for its strengthing anchorage. Because the rigidityof two kindsof archwires are different, they play distinct roles in orthodontictreatment and should be used respectively in different stages.Because of different rigidity, the two kinds of archwires bring aboutnot only orthodontic effect but also certain unfavourable effect insome treatment stages. Therefore,both two kinds of archwires havesome advantages and disadvantages. If archwires of diverse rigidityare applied in orthodontic process according to diverse regions,which contributes to optimal tooth movement and less orthodonticduration.TiNiSMA and SS are welded into CoAW(compound archwire)so that softer TiNiSMA has direct action to malposed teeth andcontributes to teeth movement, while SS of higher rigidity enhancesstabilization of anchorage teeth and avoids the negative movementof anchorage teeth.Application of CoAW can cost less orthodontic duration thanmere application of TiNiSMA.In addition, application of CoAW cansave orthodontic material.So once CoAW with advantages ofTiNiSMA and SS is applied to orthodontic treatment,it will be ofvital significance. In 1997, TiNiSMA and SS(φ=1.0mm)wereconnected together and used to expansing arch orthodontictreatment by Japanese scholars.In 2001, TiNiSMA and SS wereconnected together with riveting technology and adopted inorthodontic practice by German researchers .There are currently a few domestic researchers who arestudying and developing CoAW and are limited in StomatologySchool and Material Institute of Jilin University. Throughcooperation of the two organization, Xianchun Zhu and Xinhua Sunet al. have undertook preliminary study and acquired a series ofachievements on material structure, mechanical property andclinical application of CoAW. The objectives of this experiment:1.To do further numerical calculation of mechanical property ofCoAW by the method of three-dimensional finite element on thebasis of previous researches. 2. To optimize the structure of CoAWin order to improve orthodontic result. 3.To investigate the changedregularity of stress force exerted on malocclusion teeth andanchorage teeth by different types of CoAWs when crowdedanterior teeth and tooth extracted cases are treated . 4. To analyzemechanism of action of CoAW. 5. To provide analytical methodsand data basis for the design and manufacture of CoAW. 6. To offertheoretical guidance and lectotype standard to clinical application ofCoAW.The experimental model derived from mandible specimen of ayoung male. The mandible specimen characterizes completedentition (except for bilateral mandibular third molars), crowdingand anterior process of anterior teeth and roughly regular middleand posterior teeth alignment. CoAW is suitable for this kind ofcase. This experiment employed helico-CT to scan the mandiblespecimen by 1mm-thickness layer , finished assembly withSolidWorks technology and attained modularization of serialdentition models by finite element analysis. Thus,we can constructall kinds of malformation of dentition according to differentmalocclusion.The conclusion of this experiment : (1). CoAW has greaterapplication range of orthodontic treatment than SS . CoAW can formsuitable orthodontic force, contribute to movement of malposed teetheffectually and maintain the stabilization of anchorage teeth. (2).THE orthodontic force effect on malocclusion teeth produced byCoAW is greater than TiNiSMA but smaller than SS, we can obtainmore gentle force approximate to that produced by TiNiSMA iftheTiNi segment of CoAW was elongaged .(3)it was investigatedthat CoAW can exert less side force on posterior teeth thanTiNiSMA and SS,so CoAW have more superiority on protectinganchorage. (4). There are important social and economic profits forapplying CoAW in orthodontic treatment.