正畸热压膜材料口腔环境老化机制研究

Esthetic alternatives to conventional fixed appliances are often requested as a result of increased interest in adult orthodontics. Thanks to the development of computer-aided design/computer-aided manufacturing techniques in the past two decades, transparent thermoplastic materials have been precisely designed and fabricated into a series of clear, removable tooth aligners for orthodontics. This orthodontic treatment modality, the most renowned of which is Invisalign, becomes more and more attractive than traditional fixed appliances because it offers a number of advantages including less pain, virtually transparent and relatively short chairtime. Despite being increasingly accepted by patients, the mechanical properties and tooth-moving process of orthodontic thermplastic appliances remains unclear and most patients need mid-course correction, refinement or change directly to fixed appliances. It is surmised that the lackluster treatment results are due to the aging process of thermoplastic materials under oral environment. Since mechanical properties are decided by micro-structure of these materials, it is crucial to look into the aging mechanism, i.e. the change of mechanical properties and micro-structure during aging process, and then develop thermoplastic materials of higher performance. However, relative research on mechanical properties and aging mechanism of orthodontic thermoplastic materials remains sparse. Therefore, our study is looking into the chagne of composition, micro-structure, surface topography, mechanical and physical properties before and after thermal treatment and immersion in 37℃ artificial saliva, and trying to uncover the aging mechanisms. Futhermore, we study the composition, micro-structure, surface topography of aligners both before and after clinical application, and try to learn the aging effect of oral environment on thermoplastic materials.

无托槽隐形矫治是近年来兴起的新型牙齿矫正技术，因其舒适、美观和椅旁时间少等优点已在临床上广泛应用。然而，临床应用发现，牙齿的移动往往滞后于预期矫治效果，多数病例仍需要在矫治过程中修正预定方案和增加步骤，甚至还需转为固定矫治。研究表明，隐形矫治器的临床使用效果与其材料（热压膜材料）的老化密切相关。因此，研究热压膜材料在口腔环境下的老化机制是临床上正确选择和使用隐形矫治器、提高治疗效果的关键，对开发新型、高效的正畸专用热压膜材料也具有重要的科学意义。本项目拟研究在模拟口腔环境中常用正畸热压膜材料的老化过程，综合电子显微学、光谱学和热力学等技术，分析水、热等物理化学因素对材料的成分、分子结构、表面形貌、机械性能、流变性能和玻璃态转化温度等的影响；同时，对比研究隐形矫治器在口腔中使用前后的物理、化学和力学性能变化，从而认识材料在口腔环境中的老化机制。

无托槽隐形矫治是近年来兴起的新型牙齿矫正技术，因其舒适、美观和椅旁时间少等优点已在临床上广泛应用。然而，临床应用发现，牙齿的移动往往滞后于预期矫治效果，多数病例仍需要在矫治过程中修正预定方案和增加步骤，甚至还需转为固定矫治。研究表明，隐形矫治器的临床使用效果与其材料（热压膜材料）的老化密切相关。因此，研究热压膜材料在口腔环境下的老化机制是临床上正确选择和使用隐形矫治器、提高治疗效果的关键，对开发新型、高效的正畸专用热压膜材料也具有重要的科学意义。.研究表明，热处理可能通过去除原材料中的水分，增大了材料自由体积，导致材料刚性和强度下降，塑性增加；水分子一方面作为增塑剂，降低材料的机械性能，另一方面，材料吸收的水分进入了自由体积，材料密度增加，从而导致了刚性和强度增大，塑性下降，材料由塑性转变为脆性；体外模拟环境并不能完全解释材料在实际临床使用中的老化过程，与实验模拟采用的膜片相比较，矫治器和保持器在使用后其表面微观结构均发生明显破损。此外，复杂的口腔环境还能造成矫治器中某些痕量元素如Al的释出；本研究还发现，热和人工唾液浸泡预处理、甚至临床使用等均不会造成聚合物单体的化学和分子结构（官能团）的改变。因此，材料老化（即宏观力学性能的改变）应该与材料的微观结构（如微米尺度上材料破损），和单体的聚合度（如链的长度及其铰链程度）的变化等相关。.痕量元素的研究发现低含量的铝、钛、铁、钒、钴、镍、铬、铜、锌在未使用的保持器热塑性材料中检出，低含量的铝、镍、锌、锡在未使用的矫正器热塑性材料中检出；所有检出元素的含量均未超过成年人人体从饮食中对该成分的每日摄入量；临床佩戴使用后较使用前同种材料中同一金属成分的含量下降明显，说明材料中的金属成分可能存在释出现象；在高于材料实际临床更换频率和使用量的情况下，热塑性保持器和矫正器中金属成分的释出未对以大鼠血液为取样对象的机体样本产生影响。