Bondemark L
Department of Orthodontics, Faculty of Odontology, University of Lund, Malmö, Sweden.
Swed Dent J Suppl. 1994;99:1-148.
Magnetic forces have been incorporated into orthodontic mechanics during recent years. However, the biocompatibility of magnet alloys and the possible risk of harmful or unusual reactions in tissues exposed to static magnetic fields have been characterized as inconsistent and often contradictory. It has also been questioned whether magnetic forces have significant advantages over traditional mechanics. The present series of studies aimed to analyse the force and field properties, the biocompatibility and the clinical effects of rare earth magnets as well as to compare the efficiency of tooth movement between magnets and another force system. Samarium-cobalt magnets for molar distalization were tested in experimental models for force and field properties. The cytotoxicity of different magnet alloys (rare earth types) as well as of clinically used and recycled magnets was assessed by two in vitro methods, the millipore filter method and an extraction method. The effect of static magnetic fields on human gingival tissue and dental pulp was examined histologically for alterations in cell pattern and cell morphology. The effects of using repelling samarium-cobalt magnets for simultaneous distalization of maxillary first and second molars were analysed in individuals with Class II malocclusion. The efficiency of molar distalization was also intra-individually compared between repelling magnets and superelastic NiTi-coils in individuals with Class II malocclusion and deep bite. The magnet forces decreased approximately with the reciprocal square of the separation distance between the magnets. No fatigue of force over time could be seen. The static magnetic fields were weak and had a limited extent and the flux density dropped exponentially in all directions with increased distance from the magnets, implying a small exposure area when the magnets are used clinically. Rare earth magnets showed good biocompatibility, particularly coated magnets. However, uncoated samarium-cobalt magnets showed significant cytotoxicity. It was also found that stainless-steel-coated samarium-cobalt magnets could be recycled with maintained good biocompatibility. After exposure to static magnetic fields, normal clinical and histological conditions in the human gingival tissue and normal histological features in the human dental pulp were found. Repelling magnets were effective in producing maxillary molar distalization but some side effects like anchorage loss and molar tipping were found. The superelastic coils were shown to be even more efficient than the repelling magnets for maxillary molar distalization in individuals with Class II malocclusion and deep bite.
近年来，磁力已被应用于正畸力学中。然而，磁合金的生物相容性以及暴露于静磁场的组织中可能出现的有害或异常反应风险，其特征一直不一致且常常相互矛盾。磁力是否比传统力学具有显著优势也受到了质疑。本系列研究旨在分析稀土磁体的力和场特性、生物相容性及临床效果，并比较磁体与其他力系统之间牙齿移动的效率。用于磨牙远移的钐钴磁体在实验模型中进行了力和场特性测试。通过两种体外方法，即微孔滤膜法和萃取法，评估了不同磁合金（稀土类型）以及临床使用和回收磁体的细胞毒性。通过组织学检查静磁场对人牙龈组织和牙髓的影响，观察细胞模式和细胞形态的变化。分析了在安氏II类错牙合个体中使用排斥性钐钴磁体同时远移上颌第一和第二磨牙的效果。在安氏II类错牙合和深覆牙合个体中，还在个体内比较了排斥性磁体和超弹性镍钛线圈在磨牙远移方面的效率。磁体间的力大约随磁体间距离的平方反比减小。未观察到力随时间的疲劳现象。静磁场较弱且范围有限，磁通密度随距磁体距离增加在所有方向上呈指数下降，这意味着临床使用磁体时暴露面积较小。稀土磁体显示出良好的生物相容性，特别是涂层磁体。然而，未涂层的钐钴磁体显示出显著的细胞毒性。还发现不锈钢涂层的钐钴磁体可以回收，且生物相容性良好。暴露于静磁场后，人牙龈组织的临床和组织学状况正常，人牙髓的组织学特征正常。排斥性磁体在使上颌磨牙远移方面有效，但发现了一些副作用，如支抗丧失和磨牙倾斜。在安氏II类错牙合和深覆牙合个体中，超弹性线圈在使上颌磨牙远移方面比排斥性磁体更有效。
