Changes of masticatory function and biomechanical behavior in growing Mandible.

本研究的目的是利用三维定量CT （3DQCT）和三维有限元法（3DFEM）研究下颌畸形骨密度分布的年龄相关性变化，并阐明其形成机制。对47例骨骼畸形患者和20例正常受试者（6 ~ 27岁）进行了评估。三维骨密度观察和有限元分析结果表明：18岁以下的畸形下颌骨多数出现高密度偏差，与形态位移相吻合。然而，在20岁以上的受试者中，高密度区域被对称地排列，以防止形态变形。肌肉负荷产生的等效应力分布与骨密度一致。正常受试者和20岁以上畸形受试者的应力分布呈对称分布。然而，在18岁以下的畸形下颌骨中，应力分布偏向于患侧。通过正常和畸形受试者的对比，咀嚼肌产生的机械应力影响下颌骨密度的分布，导致生长的形态改变。在出生后发育过程中出现的骨骼畸形是由咀嚼不平衡引起的。然而，在髁突生长完成后，下颌骨密度适应了其不平衡的机械环境。这些发现表明，预防性的正畸治疗，如在早期消除错牙合的功能干扰，应该会取得成功的结果。

The purpose of this study was to investigate the age-related changes in the bone density distribution and to clarify the mechanism of mandibular deformity using 3-dimensional quantitative CT (3DQCT) and a 3-dimensional Finite Element Method (3DFEM).Forty-seven individuals with skeletal deformity and twenty normal subjects (6 to 27 years old) were evaluated.The results obtained from the 3-dimensional abservation of bone density and the FE analysis were as follows : Most cases of deformed mandibles under 18 years of age showed high-density deviation which coincided with the morphological displacement. However, in subjects more than 20 years old, high-density areas were arranged symmetrically against the morphological deformation. The distribution of equivalent (mieses) stress generated by muscle loading coincided with the bone density. In normal subjects and deformed subjects over 20 years old, symmetrical stress distribution was observed. However, in deformed mandibles under 18 years old, stress distribution was biased toward the affected side.Based on this comparison of normal and deformed subjects, the mechanical stress generated by masticatory muscles affects the distribution of mandibular bone density and leads to morphological changes in growth. The skeletal deformity which appeared during postnatal growth was caused by imbalanced mastication. However, after condylar growth was complete, mandibular bone density adapted to its imbalanced mechanical environment. These findings suggest that preventive, orthodontic treatment, such as eliminating the functional interference of the malocclusion at an early stage, should give successful results.