Purpose

The objective of this study was to evaluate the anterior tooth movement without and with bonded fixed orthodontic retainers under incremental loading conditions.

Materials and methods

Six extracted mandibular anterior human teeth were embedded in acrylic resin in True Form I Arch type and 3D reconstruction of Digital Volume Tomography (DVT) images (0.4 mm³ voxels) were obtained. The anatomy of each tooth was segmented and digitally reconstructed using 3D visualization software for medical images (AMIRA, FEI SVG). The digital models of the teeth were repositioned to form an arch with constant curvature using a CAD software (Rhinoceros) and a base holder was designed fitting the shape of the roots. The clearance between the roots and their slot in the holder was kept constant at 0.3 mm to replicate the periodontal ligament thickness. The holder and the teeth were then manufactured by 3D printing (Objet Eden 260VS, Stratasys) using a resin material for dental applications (E = 2–3 GPa). The 3D-printed teeth models were then positioned in the holder and the root compartments were filled with silicone. The procedure was repeated to obtain three identical arch models. Each model was tested for tooth mobility by applying force increasing from 5 to 30 N with 5 N increments applied perpendicular on the lingual tooth surface on the incisal one third (crosshead speed: 0.1 mm/s). The teeth on each model were first tested without retainer (control) and subsequently with the bonded retainers (braided bonded retainer wire; Multi-strand 1 × 3 high performance wire, 0.022″ × 0.016″). Tooth displacement was measured in terms of complicance (F/Δ movement) (N/mm) using custom-built optoelectronic motion tracking device (OPTIS) (accuracy: 5 µm; sampling rate: 200 Hz). The position of the object was detected through three LEDs positioned in a fixed triangular shape on a metal support (Triangular Target Frame). The measurements were repeated for three times for each tooth. Data were analyzed using mixed model with nesting (alpha = 0.05).

Results

The use of retainer showed a significant effect on tooth mobility (0.008 ± 0.004) compared to non-bonded teeth (control) (0.014 ± 0.009) (p < 0.0001). The amount of displacement on the tooth basis was also significantly different (p = 0.0381) being the most for tooth no. 42 (without: 0.024 ± 0.01; with: 0.012 ± 0.002) (p = 0.0018). No significant difference was observed between repeated measurements (p = 0.097) and the incremental magnitude of loading (5–30 N: 0.07 ± 0.01–0.09 ± 0.02) (p > 0.05).

Conclusion

Mandibular anterior teeth showed less tooth mobility when bonded with stainless steel wire as opposed to non-bonded teeth but the tooth mobility varied depending on the tooth type. Intermittent increase in loading from 5 to 30 N did not increase tooth displacement.

中文翻译：

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不使用固定式正畸固定器和使用固定式正畸固定器的情况下的牙齿移位：使用三角靶架和光电运动跟踪装置进行3D分析

目的

这项研究的目的是评估在递增负荷条件下不使用粘结固定正畸固定器和使用粘结固定正畸固定器的前牙运动。

材料和方法

将六颗下颌前牙拔出，以True Form I Arch类型嵌入到丙烯酸树脂中，并进行3D重建数字体层摄影（DVT）图像（0.4 mm ³获得体素）。使用3D可视化软件对医学图像（AMIRA，FEI SVG）进行分割和数字重建每个牙齿的解剖结构。使用CAD软件（Rhinoceros）重新定位牙齿的数字模型，以形成具有恒定曲率的牙弓，并设计了适合牙根形状的基托。牙根与其在固定器中的缝隙​​之间的间隙保持恒定在0.3毫米，以复制牙周膜的厚度。然后使用树脂材料（E = 2-3 GPa）通过树脂材料的3D打印（Objet Eden 260VS，Stratasys）制造支架和牙齿。然后将3D打印的牙齿模型放置在支架中，并用硅树脂填充牙根室。重复该过程以获得三个相同的足弓模型。通过从5到30 N增加的力（垂直于切齿的舌齿表面垂直施加5 N的增量）施加5 N的力来测试每个模型的牙齿移动性（十字头速度：0.1 mm / s）。首先对每个模型上的牙齿进行测试，不使用固定器（对照），然后使用粘结的固定器（编织的粘结固定器丝；多股1×3高性能导线，0.022“×0.016”）。使用定制的光电运动跟踪设备（OPTIS）（精度：5 µm；采样率：200 Hz），根据柔韧性（F /Δ运动）（N / mm）测量牙齿的位移。通过三个固定在金属支架（三角形目标框架）上的三角形LED来检测物体的位置。每个牙齿重复测量三次。

结果

与未粘结的牙齿（对照组）（0.014±0.009）相比，使用保持架对牙齿的活动性有显着影响（0.008±0.004）（p <0.0001）。以齿为基础的位移量也有显着差异（p = 0.0381），这是齿数最多的。42（无：0.024±0.01；有：0.012±0.002）（p = 0.0018）。重复测量（p = 0.097）与增加的载荷量（5–30 N：0.07±0.01–0.09±0.02）之间无显着差异（p> 0.05）。

结论

下颌前牙与不粘结的牙齿相比，用不锈钢丝粘结时显示出较小的牙齿活动性，但是牙齿活动性随牙齿类型而变化。负荷从5 N间歇增加到30 N并没有增加牙齿的位移。