Department of Orthodontics, Shanghai Ninth People's Hospital, College of Stomatology, National Clinical Research Center for Oral Diseases, Shanghai Key Laboratory of Stomatology & Shanghai Research Institute of Stomatology, Shanghai Jiao Tong University School of Medicine, No. 639 Zhizaoju Road, Huangpu District, Shanghai, 200011, PR China.
BMC Oral Health. 2024 May 14;24(1):561. doi: 10.1186/s12903-024-04325-3.
Prefabricated myofunctional appliance can guide tooth eruption, improve dentition alignment, correct myofunctional disorders and harmful oral habits. However, its application to skeletal discrepancy may result in unsatisfactory tooth inclination. This study aimed to construct a novel appliance with overjet design to avoid this side effect and investigated its shape and mechanical changes under occlusion using three-dimensional finite element method.
We established three samples of prefabricated myofunctional appliances. The first one was edge to edge without overjet, and the outer shield of both jaws were flattened. The second one was 3 mm overjet with stepped the outer shield. The last one was 3 mm overjet, and the outer shield of both jaws were flatted, which meant the front wall of lower jaw was strengthened with bumper, termed as lower bumper. A complete dentition model was applied to the study. 150 N occlusal force was applied to each type of appliance and the deformation displacement and the changes in stress was recorded.
The deformation was significant in the incisors regions, especially in the vertical and lateral dimensions. The maximum displacements of 3 mm overjet with step shield group were 7.08 mm (vertical), 3.99 mm (lateral), and 2.90 mm (sagittal), while it decreased to 3.92 mm(vertical), 1.94 mm (lateral), and 1.55 mm (sagittal) in overjet with bumper group. Moreover, the upper molar regions exhibited higher vertical and sagittal displacement in 3 mm overjet with step shield group, which were 3.03 mm (vertical) and 1.99 mm (sagittal), and the bumper design could decrease the maximum displacement to 1.72 mm (vertical) and 0.72 mm (sagittal). In addition, the Von Mises stress of appliances was analyzed, and results indicated that 3 mm overjet with step shield generated higher stress than other groups, with the maximum Von Mises stress was 0.9387 MP, which were 0.5858 and 0.5657 MP in edge to edge group and 3 mm overjet with lower bumper group, respectively.
The prefabricated myofunctional appliances may cause deformation during occlusion. Compared to step shield group, the application of lower bumper exhibited better resistance to occlusal force.
预制肌功能矫治器可引导牙齿萌出、改善牙列排列、纠正肌功能障碍和不良口腔习惯。然而，其在骨骼错畸形中的应用可能导致牙齿倾斜度不理想。本研究旨在构建一种具有前伸设计的新型矫治器，以避免这种副作用，并通过三维有限元法研究其在咬合下的形状和力学变化。
我们建立了三种预制肌功能矫治器样本。第一种为无前伸的边缘接触，上下颌外盾为平面。第二种为 3mm 前伸，外盾为台阶状。第三种为 3mm 前伸，上下颌外盾为平面，即下颌前壁用保险杠加强，称为下颌保险杠。采用全牙列模型进行研究。每种矫治器施加 150N 的咬合力，记录变形位移和应力变化。
切牙区变形明显，尤其是垂直和侧向尺寸。台阶状外盾 3mm 前伸组的最大位移分别为 7.08mm（垂直）、3.99mm（侧向）和 2.90mm（矢状），而下颌保险杠组则减小至 3.92mm（垂直）、1.94mm（侧向）和 1.55mm（矢状）。此外，上颌磨牙区在台阶状外盾 3mm 前伸组中表现出更高的垂直和矢状位移，分别为 3.03mm（垂直）和 1.99mm（矢状），保险杠设计可将最大位移减小至 1.72mm（垂直）和 0.72mm（矢状）。此外，对矫治器的 Von Mises 应力进行了分析，结果表明，台阶状外盾 3mm 前伸组产生的应力高于其他组，最大 Von Mises 应力为 0.9387MP，边缘接触组和 3mm 前伸下颌保险杠组分别为 0.5858MP 和 0.5657MP。
预制肌功能矫治器在咬合时可能会发生变形。与台阶状外盾组相比，下颌保险杠的应用表现出更好的抗咬合能力。
