Ammann Rémi, Tanner Christine, Schulz Georg, Osmani Bekim, Nalabothu Prasad, Töpper Tino, Müller Bert
University of Basel, Biomaterials Science Center, Department of Biomedical Engineering, Allschwil, Switzerland.
University of Basel, Biomaterials Science Center, Department of Clinical Research, Basel, Switzerland.
J Med Imaging (Bellingham). 2022 May;9(3):031509. doi: 10.1117/1.JMI.9.3.031509. Epub 2022 Jun 16.
The morphology of a polymer aligner, designed according to an orthodontic treatment plan, determines clinical outcomes. A fundamental element of orthodontic tooth movement with aligner treatment is the fit of the aligner's surface to the individual teeth. Gaps between the aligner and teeth do occur because current aligner fabrication is not capable of completely reproducing the complex anatomy of the individual denture. Our study aims at a quantitative three-dimensional assessment of the fit between optically transparent aligners placed on a polymeric model of the upper dental arch for two thermofoil thicknesses at preselected thermoforming temperatures.
Using an intraoral scan of a subject's upper dental arch, eight models were printed using a stereolithographic system. A series of eight NaturAligners was manufactured with a pressure molding process, using thermofoils with thicknesses of 550 and and preselected process temperatures between 110°C and 210°C. These aligners placed on the corresponding models were imaged by an advanced micro computed tomography system. The aligners and the models were segmented to extract the gaps and aligners' local thicknesses as a function of the processing temperature for the two foil thicknesses.
The results indicate that the aligners show a better fit when the foils are processed at higher temperatures. Nevertheless, processing temperatures can be kept below 150°C, as the gain becomes negligible. Thermal processing reduces the average thickness of the aligners to 60% with respect to the planar starting foil. These thickness distributions demonstrate that the aligners are generally thicker on the occlusal surfaces of molars and premolars but thinner around the incisors and buccal as well as on oral surfaces.
Hard x-ray tomography with micrometer resolution is a powerful technique employed to localize the gaps between aligners and teeth, and it also enables film thickness measurements after thermoforming. The thicker film on the occlusal surfaces is most welcome because of aligner abrasion during wear. The NaturAligner surfaces consist of a -thin cellulose layer, and thus the microplastics released via abrasion of less than this thickness are expected to be substantially less critical than for other commercially available, optically transparent aligners.
根据正畸治疗计划设计的聚合物矫治器的形态决定临床效果。使用矫治器进行正畸牙齿移动的一个基本要素是矫治器表面与单个牙齿的贴合度。由于目前的矫治器制作无法完全再现个体牙列的复杂解剖结构，矫治器与牙齿之间确实会出现间隙。我们的研究旨在对在预选热成型温度下，两种热箔厚度的光学透明矫治器放置在上颌牙弓聚合物模型上时的贴合度进行定量三维评估。
使用受试者上颌牙弓的口内扫描数据，通过立体光刻系统打印出八个模型。采用压力成型工艺，使用厚度为550以及在110°C至210°C之间预选工艺温度的热箔，制作了一系列八个NaturAligner矫治器。放置在相应模型上的这些矫治器由先进的微型计算机断层扫描系统成像。对矫治器和模型进行分割，以提取间隙以及作为两种箔厚度的加工温度函数的矫治器局部厚度。
结果表明，当箔在较高温度下加工时，矫治器显示出更好的贴合度。然而，加工温度可保持在150°C以下，因为增益变得微不足道。热加工使矫治器的平均厚度相对于平面起始箔减少至60%。这些厚度分布表明，矫治器通常在磨牙和前磨牙的咬合面上较厚，但在门牙周围、颊侧以及口腔表面较薄。
具有微米分辨率的硬X射线断层扫描是一种强大的技术，可用于定位矫治器与牙齿之间的间隙，并且还能在热成型后进行薄膜厚度测量。由于矫治器在佩戴过程中的磨损，咬合面上较厚的薄膜是非常受欢迎的。NaturAligner矫治器表面由一层薄的纤维素层组成，因此通过磨损释放的厚度小于此厚度的微塑料预计比其他市售的光学透明矫治器的危害要小得多。
