Changes of masticatory function and biomechanical behavior in growing Mandible.

应用三维定量CT(3DQCT)和三维有限元方法(3Dfem)对47例骨骼畸形患者和20例6~27岁正常人的骨密度进行了三维观察和有限元分析，结果表明：18岁以下下颌骨畸形患者多表现为高密度差，与形态移位基本一致。然而，在20岁以上的受试者中，高密度区对称排列，与形态变形相反。肌肉负荷产生的等效应力(Mieses)分布与骨密度一致。在20岁以上的正常人和畸形者中，观察到了对称的应力分布。然而，18岁以下畸形下颌骨的应力分布偏向于患侧，在此基础上比较正常和畸形受试者，咀嚼肌产生的机械应力影响下颌骨的骨密度分布，导致生长发育的形态变化。出生后发育过程中出现的骨骼畸形是由于咀嚼不平衡引起的。然而，在髁突发育完成后，下颌骨密度适应了其不平衡的力学环境。这些发现表明，预防性的正畸治疗，例如在早期阶段消除错(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.