【作者】 张超；

【导师】 孙新华；

【作者基本信息】 吉林大学 ， 口腔医学， 2014， 博士

【摘要】 正畸临床上对矫治弓丝的应用大多遵循弓丝尺寸由细到粗，弓丝刚度由小到大的顺序，通常先使用镍钛弓丝，然后逐步过渡到使用不锈钢弓丝。单独应用镍钛弓丝或不锈钢弓丝存在着很多不足之处，特别是牙弓不同部位的牙齿需要安放不同刚度和性能的弓丝情况下，单纯使用一种弓丝无法满足临床的需要。复合矫治弓丝（Composite Arch wire, CAW）是将镍钛合金弓丝和不锈钢弓丝连接成一根包含两种材质的矫治弓丝，能在需要移动的牙段应用镍钛弓丝，需要提供支抗的牙段应用不锈钢弓丝，利用力量柔和的镍钛弓丝直接作用于错位牙，有效移动牙齿；同时利用不锈钢弓丝较大的刚度来加强支抗牙的稳定，防止负移动的发生。2011年吉林大学材料学院李洪梅、孙大谦采用激光焊接加中间层的方法研制出符合临床需求的复合弓丝。加铜中间层激光焊接复合弓丝性能优良，满足正畸矫治弓丝使用性能的要求，于2011年获得专利。新一代的激光焊接加铜中间层复合弓丝性能优良，其应用于正畸临床将会大大提高矫治的效率，带领正畸矫正技术进入一个新的发展阶段。新一代的激光焊接加铜中间层复合弓丝由两端的镍钛部分和不锈钢部分构成，两种材料都会因腐蚀而导致金属离子的析出，此外，复合弓丝焊接头处引入了同样有可能引起毒性反应的铜元素，在焊接过程之后复合弓丝是否能够具备相当的抗腐蚀能力，铜离子的析出量是否在生物安全范围内是目前亟需研究的问题，因此需要通过一系列的实验研究来探索复合弓丝在模拟口腔环境下的抗腐蚀性能。同其他合金材料一样，复合弓丝的抗腐蚀能力也依赖于表面钝化膜的形成,在钝化膜受到破坏时自我修复能力不足，则可能引起深层材料的腐蚀，导致有害离子的析出。口腔是一个极其复杂的环境，在一种新型生物材料应用于临床前，有必要谨慎的研究其发挥功能的环境以及与环境的相互作用关系，特别是口腔中各种可能引起材料腐蚀性能变化的因素，如pH值、氯离子、氟离子以及各种蛋白质的参与，都应逐一探索和讨论；尤其是复合弓丝应用于临床时，不是处于一个静态的唾液浸泡过程，而是不断受到矫正错位牙的扭正力以及咀嚼时食物的推挤力，因此还有必要进行复合弓丝的应力腐蚀研究；复合弓丝的激光焊接不只是让自体金属发生重熔再结晶，熔区元素成份有改变，有铜元素的介入会发生原电池阳极腐蚀，因此对复合弓丝进行相关的电化学实验研究也是十分重要的。综上，理化性能和机械性能优良的激光焊接加铜中间层复合弓丝的抗腐蚀性能在其应用临床时是极其重要的，但相关研究仍未见报道。本文模拟口腔实际环境对激光焊接加铜中间层镍钛形状记忆合金和不锈钢复合弓丝的抗腐蚀性能进行了研究。通过静态浸泡实验和电化学实验，以及加速腐蚀实验的结果，初步评价了复合弓丝在不同的pH值、氟离子浓度、蛋白浓度和负载值下的金属离子析出情况以及表面腐蚀微观形貌，结合电化学实验结果、失重和离子析出结果，得出了复合弓丝在不同侵蚀性环境中的抗腐蚀性能参数，进一步判定复合弓丝的抗腐蚀性能和生物安全性，为复合弓丝的临床应用奠定基础，也为其进一步改良和临床应用提供了实验和理论依据。本研究结合临床使用条件，模拟口腔环境全面的对复合弓丝进行材料学和生物学的评价，为复合弓丝在临床的使用和推广提供基础，并为口腔用新型金属材料的抗腐蚀性研究提供实验路线和参考。在不同pH人工唾液和含氯溶液腐蚀情况：含氯溶液中复合弓丝失重量和铜离子析出量明显大于人工唾液组，酸性唾液组失重和铜离子析出略高于中性唾液组。环状极化过程中，三种介质的保护电位都高于自腐蚀电位，材料的再钝化能力有限。中性唾液组的点蚀电位高于酸性唾液组，但腐蚀电流密度低于酸性组。中性唾液组复合弓丝表面相对平滑，含氯溶液中腐蚀后表面更加粗糙，裂隙的直径较人工唾液组更大，深度也明显增加。酸性唾液组的腐蚀形貌与中性组相似，略有严重趋势但程度不及含氯溶液组。复合弓丝在人工唾液中的抗腐蚀能力高于含氯溶液，酸碱度的改变会影响复合弓丝在人工唾液中的腐蚀情况，酸性条件使保护性氧化膜更容易破裂，导致离子析出和腐蚀加速。含氟溶液中，低氟溶液的腐蚀电位与单纯人工唾液相似，但高氟溶液腐蚀电位明显降低，在阴极极化后，电流迅速增大。单纯人工唾液组的极化曲线呈现出滞后环状，含氟溶液的环状回扫曲线有与先前扫描重合的趋势。扫描电镜下见含氟组有明显的点状腐蚀坑，高氟组腐蚀坑直径和深度大于低氟组，铜离子的析出量和重量损耗也较多。随着氟浓度的增加，复合弓丝的抗腐蚀能力减弱，复合弓丝在低氟溶液中具有较强的抗腐蚀能力，高氟溶液能够降低复合弓丝的抗腐蚀性能，然而，即使氟加速了复合弓丝的腐蚀进程，但整体的铜离子析出量仍然在WHO规定限度以内。含蛋白溶液中，低浓度蛋白溶液复合弓丝腐蚀电位明显降低，两种浓度的蛋白溶液点蚀电位均低于单纯唾液组。静态腐蚀后低蛋白组表面更粗糙，有数目较多的点蚀坑的出现。随蛋白浓度的升高，表面腐蚀并未明显加重，腐蚀坑的深度和数目都不及低蛋白组。低蛋白组铜离子的析出量在三组腐蚀介质中最多，高蛋白溶液静态腐蚀后与单纯唾液组相比，铜离子的析出量有增加，但失重量并未明显增加。总的来说，复合弓丝焊接区在含蛋白的溶液中表现出良好的抗腐蚀性能，低浓度的蛋白溶液降低了复合弓丝的抗腐蚀性能，高浓度的蛋白溶液会减少这种效应。蛋白质可以在材料表面形成薄膜，作为离子扩散的屏障，虽然可以减少铜离子的析出，但是也阻碍了人工唾液中钙、磷离子的沉积。高浓度蛋白并没有使腐蚀明显加速，可能是由于蛋白沉积在样品表面的厚度增加，进一步阻碍了氧的侵入和离子的析出，但是具体的机制仍有待于进一步的研究表明。不同pH条件和不同氟浓度人工唾液中的应力腐蚀：复合弓丝浸泡于酸性、中性和含氟人工唾液四周后表面无明显降解发生，无论是否施加应力；施加应力组在三点弯曲应力的张力侧表面更加粗糙，随着弯曲位移的增大，中间层表面更加粗糙，腐蚀坑呈现不规则的形貌，能谱分析结果见金属表面腐蚀坑的主要元素成分含有氧和磷。无论酸性还是中性人工唾液，应力的施加都会导致铜离子析出增加，增加量与施加的应力位移成正比。三点弯曲应力作为外加载荷，能够引起复合弓丝的形变引起材料表面氧化膜的点状破裂，随后裂隙在金属表面延伸加剧保护膜的破损，腐蚀介质因此而接触到保护膜下方的暴露金属引起进一步的腐蚀。在应力作用下，氢离子渗入材料并沿着位移施加点扩散。随后氢离子和氟离子结合，形成侵蚀性更强的氢氟酸，加速中间层铜离子的溶解。在高氟和大应力的协同作用下，复合弓丝中间层的抗腐蚀能力明显减弱，但高氟环境和大应力情况在临床上甚为少见。总的来说，复合弓丝在模拟口腔环境的腐蚀过程中表现出良好的抗腐蚀能力。在无机离子、有机蛋白和应力的加速腐蚀条件下，复合弓丝仍然表现出较好的抗腐蚀性能，满足临床正畸弓丝应用的需求。电化学实验和静态腐蚀实验是检测口腔用金属材料的重要手段，结合两种实验的结果可以评估不同模拟口腔环境的腐蚀条件对金属材料腐蚀行为的影响及材料的抗腐蚀能力，本实验的结果为口腔金属材料的进一步发展和改良提供相应的理论依据。更多还原

【Abstract】 The clinical application of the orthodontic archwire mostly follow the size andstiffness ascending order, which usually starts from the first use of nickel-titaniumarch wire, and then gradually transforms to the use of stainless steel arch wire. Thereare many shortcomings of using nickel-titanium or stainless steel arch wire alone.The use of one simple kind of arch wire could not meet clinical needs, especiallyunder the circumstances that different parts of the dental arch require the placementof different stiffness and performance of arch wires. Composite archwire (CAW) isformed by solder connection of nickel-titanium and stainless steel arch wire.Nickel-titanium part could be used in the part of dental arch which containsmalposed teeth, and stainless steel part could be used in the part which need toprovide anchorge. CAW combines the advantages of the individual material tocorrect malposed teeth whilst maintain the stability of anchored teeth. Li Hongmeiand Sun Daqian from the department of Materials process in Jilin Universitydeveloped the new CAW which could satisfy clinical needs in2011by using laserwelding and copper interlayer, and the design was patented in2011. CAW withcopper interlayer helds good mechanical properties and the application of CAW inclinical treatment will lead orthodontic technology into a new stage of development.The corrosion of nickel-titanium part and stainless steel part in CAW would result inthe precipitation of metal ion, in addition, the interlayer of CAW contains purecopper metal. Whether the precipitation of copper ions in oral after welding is withinthe limit of biosafety is urgently needed to be tested. Similar as other alloy materials,the corrosion resistance of CAW is also dependent on the passivation film formed onthe surface, the repairation ability of which to is limited. The damage of passivationfilm may cause further etch of deep material, leading to harmful ion precipitation.The effects of corrosion on CAW contain mainly three aspects: First, the reduction of mechanical properties like tensile and elastic strength, or even breakage in clinic.Secondly, the damage of oxide film on the wire surface. The corrosion concave couldincrease friction and prolong the clinical course of orthodontic treatment. Thirdly,the local oral tissue and systemic adverse reactions caused by the release of metalions after corrosion.The oral cavity is an extremely complex environment with a variety of factors whichcould effect the corrosion of material, such as the pH value, chloride, fluoride andvarious proteins. Before the clinical application of a new type of biological material,it is necessary to carefully study and explore the environment in which it mustfunction and also it effect. It is also important to discuss the stress corrosion of CAW,since it is not simple soaking in a static condition when used in clinic, but isconstantly subjected to the twisting force of correcting misaligned teeth, as well aschewing food pushing force. Laser welding was not a simple autologous metalremelting recrystallization process, the elements in the melting zone are changedwhere brings the involvement of copper. The primary cell anode corrosion of copperwould occur, therefore it is necessary to study the related electrochemical corrosionof CAW. In summary, the corrosion resistance of laser welding CAW with excellentphysical and mechanical properties in its clinical application is extremely important,but the related research has not yet been studied.In this study, the corrosion resistance of laser welding CAW with copper interlayer insimulated oral cavity environment was studied. A preliminary evaluation of the metalion release and micro-appearance surface corrosion of CAW was explored throughstatic immersion test and electrochemical assay in different pH value, fluoride ionconcentration, protein concentration and load values. The corrosion resist anceparameters in various aggressive environments were obtained by combining theelectrochemical results with weight loss and ion precipitation results. The corrosionresistance and bio-security of CAW was predicted not only to determine and lay thefoundation the clinical application of CAW in the process of clinical application, butalso to provide experimental and theoretical basis for its further improvement. In this study, the comprehensive materials science and biology evaluation of CAW by acombination of clinical condition and simulated oral environment, could provide abasis for its clinical use and promotion, and provide experimental route and referenceto the corrosion resistance studies with other new oral metal materials.The corrosion condition of CAW in chlorine solution and artificial saliva at differentpH: the copper ions precipitate and weight loss were significantly greater in chlorinesolution than artificial saliva group, and the weight loss and copper ions precipitatein acidic saliva group were slightly above the neutral group. The protective potentialof three medium is higher than the corrosion potential in cyclic polarization processindicates the limited capacity of re-passivation. Pitting potential was higher and andcorrosion current densities were lower in acidic saliva group than neutral group. Thesurface of CAW after electrochemical corrosion is relatively smooth, but there arealso a small number of cracks generated, especially in chlorine solution with morerough, deeper, and etch pits. The corrosion morphology in acidic saliva was similarto neutral saliva, but not severe as chlorine solution group. The corrosion resistanceof CAW in artificial saliva was higher than in chlorine solution, and acidity changescould affect the corrosion resistance in artificial saliva. The protective oxide film ismore prone to rupture in acidic condition, leading to accelerate ion precipitation andcorrosion.In different values of fluorine-containing solution: the corrosion potential oflow-fluoride solution was similar as simple artificial saliva, but significantly lowercorrosion potential was found in high-fluoride solution with the current increasingrapidly after cathodic polarization. The cyclic retrace curve in fluorinated solutionhas the trend of coincide with the previous scan, whereas the polarization curve ofsimple artificial saliva group shows a typical hysteresis loop. The microscopemorphology of fluorinated group showed obviously visible etch pit, andhigh-fluoride group appear greater diameter and depth of corrosion pits thanlow-fluoride group, along with greater copper ion precipitation amount and weightloss. With the increase of the concentration of fluoride, the corrosion resistance of CAW decreased. CAW has strong corrosion resistance in low fluoride solution, andhigh-fluoride could reduce the corrosion resistance. However, even fluorideaccelerate the corrosion process of CAW, the overall amount of copper ionsprecipitation still within the specified limit of WHO.In different values of protein-containing solution: the corrosion potential oflow-protein group was significantly reduced. The corrosion current densities of threegroups were similar. The microstructure of low-protein group were rough with pits,but were not significantly increased as the values of protein concentration. Theprecipitation amount of copper ions in low-protein group was most, but the weightloss was not obvious. In general, CAW showed good corrosion resistance in solutionscontaining protein. Low protein concentration reduces the corrosion resistance ofCAW, while high concentrations of protein would reduce this effect. Protein couldform film on the surface as ion diffusion barrier, while the precipitation of copperions can be reduced as well as hinder calcium and phosphorus ions from artificialsaliva deposited. The reason for high protein concentrations did not significantlyaccelerate the corrosion process may be the increase of deposited protein layerthickness on the sample surface, which further hinder the intrusion of oxygen ions.However the specific mechanism remains to be further studied.The corrosion condition of CAW under stress conditions and different acidities ordifferent concentrations of fluoride: the surface of CAW was intact withoutsignificant degradation occurs after immersed in acidic and neutral artificial saliva,regardless of the applied stress; the tension side of three-point bending stress showedrougher surface with the increase of bending displacement. The corrosion p its oninterlayer also showed irregular morphology. The main elements composition ofinterlayer contain oxygen and phosphorus according to the energy spectrum analysis.Applied stress would cause increase of copper ions precipitation either in acidic orneutral saliva, and the amount of increase is proportional to the increase of appliedstress. Three-point bending stress as the applied load, could cause deformation ofCAW and the rupture of oxide film on the surface. Then the rupture subsequently extended to exacerbate the breakage of the metal protective film which made thebottom metal expose to corrosive media leading to further erosion. Three-pointbending stress can cause rupture of the passivation film of interlayer surface,followed by hydrogen ions penetrate in the point of displacement and spread alongthe stress. Then hydrogen and fluoride ions could combine to form corrosivehydrofluoric acid and accelerate the dissolution of copper interlayer. Under thesynergy action of high fluorine and large stress, the corrosion resistance of CAWinterlayer significantly reduced, which is an even rare condition in clinical treatment.Overall, CAW showed good corrosion resistance in simulated oral environment. Itstill exhibits corrosion resistance in inorganic ion, organic protein and applied stressthat could meet the needs of clinical orthodontic arch wire applications.Electrochemical experiment and static corrosion experiment are important means todetect oral metallic materials corrosive resistance, and combine the results of thesetwo methods could effective assess the influence of different simulated oralenvironment on the corrosion behavior of metallic materials and corrosion resistanceof the material. The test methods and results in this study could provide theappropriate theoretical basis for further development and improvement of dentalmetallic materials.更多还原