State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, National Clinical Research Center for Oral Diseases, Shaanxi Clinical Research Center for Oral Diseases, Department of Orthodontics, School of Stomatology, Air Force Medical University, Xi'an, 710032, China.
BMC Oral Health. 2024 Oct 29;24(1):1313. doi: 10.1186/s12903-024-05114-8.
The Functional Clear Aligner (FCA) is a novel orthodontic appliance designed for the treatment of Class II malocclusion with mandibular retrognathia in adolescents. The aim of this study was to investigate the biomechanical characteristics of the masticatory muscles, jawbone, and temporomandibular joint (TMJ) during mandibular advancement using either FCA or Class II elastics combined with clear aligner (Class II elastics) through finite element analysis.
A 3D finite element model of the 'muscle-jawbone-TMJ-appliance' system was constructed based on CBCT and MRI images of a boy with skeletal Class II malocclusion. Masticatory muscles included masseter, temporal, medial pterygoid, and lateral pterygoid muscles. The TMJ consists of the temporal bone's glenoid fossa, disc, and mandibular condyle. To observe the biomechanical characteristics of the muscles and TMJ during orthodontic appliance wearing and the retention phase, two different protocols were used: Model 1: The mandibular advancement using FCA; Model 2: The mandibular advancement using Class II elastics.
The FCA group produced greater and more coordinated masticatory muscle forces compared to the Class II elastics group. Temporal and masseter muscles exhibited the most pronounced variation in muscle strength during mandibular advancement. The FCA group exhibited greater TMJ region stress compared to the Class II elastics group. Interestingly, the stress on the articular discs in both models decreased over time. Tensile stresses were observed in both the condyle and the posterior region of the articular fossa.
During skeletal Class II malocclusion treatment, masticatory muscle forces and stress on the TMJ were higher in the FCA group compared to the Class II elastics group. In both models, stress cushioning was provided by the articular disc.
功能性透明矫正器（FCA）是一种新颖的正畸矫治器，专为青少年下颌后缩的 II 类错颌畸形设计。本研究旨在通过有限元分析，研究使用 FCA 或 II 类弹性体联合透明矫正器（II 类弹性体）进行下颌前伸时咀嚼肌、颌骨和颞下颌关节（TMJ）的生物力学特征。
根据一位骨骼 II 类错颌畸形男孩的 CBCT 和 MRI 图像，构建了“肌肉-颌骨-TMJ-矫治器”系统的三维有限元模型。咀嚼肌包括咬肌、颞肌、翼内肌和翼外肌。TMJ 由颞骨的关节窝、盘和下颌骨的髁突组成。为了观察矫治器佩戴和保持阶段咀嚼肌和 TMJ 的生物力学特征，使用了两种不同的方案：模型 1：使用 FCA 进行下颌前伸；模型 2：使用 II 类弹性体进行下颌前伸。
与 II 类弹性体组相比，FCA 组产生的咀嚼肌力更大且更协调。颞肌和咬肌在进行下颌前伸时肌肉力量变化最明显。与 II 类弹性体组相比，FCA 组的 TMJ 区域的应力更大。有趣的是，随着时间的推移，两个模型的关节盘上的应力都降低了。在髁突和关节窝后区都观察到拉伸应力。
在骨骼 II 类错颌畸形治疗中，FCA 组的咀嚼肌力和 TMJ 上的应力高于 II 类弹性体组。在两个模型中，关节盘都提供了应力缓冲。
