MORPHOLOGIC AND FUNCTIONAL ANALYSIS OF MASTICATOR MUSCLE BASED ON THE CARACTERISTICS OF CLEIDOCRANIAL DYSPLASIA

目的：利用锁骨颅骨发育不良的特点，阐明咀嚼肌功能对下颌骨运动的影响、咀嚼肌功能的比较性变化以及与咬肌功能低下相关的形态特征，以明确咀嚼肌各肌功能对口颌系统的影响。方法：对3例锁骨颅骨发育不良症患者的形态特征进行观察。获得咬肌和颞肌的肌电图。结果：本研究的形态特征为：(A)颧弓与发育不良的颧骨不连续；(B)下颌升支具有平行的边缘；(C)冠突向上和/或向后；(D)咬肌厚度小于年龄和性别匹配的对照组。面肌肌电分析显示：(5)咬肌双侧咀嚼反应低，颞肌反应强。讨论：由于咬肌起源于颧弓，患者颧弓不连续可能导致对咀嚼负荷的不稳定或阻力降低。这些情况被认为是导致咬肌体积小、功能减退，颞肌功能亢进和明显的肌电模式的结果。作为对咬肌功能减退的补偿，其他咀嚼肌可能会发展为过度咀嚼功能。

Purpose : The purpose of this research were to clarify the each masticator muscle function to the stomatognathic system, which were the effect of masticator muscle function to the mandiblar movement, the compasational change in masticator muscle function and the morphological characteristics associated to the hypofunction of the masseter muscle, with application of the characteristics of cleidocranial dysplasia (CCD).Methods : The morphologic characteristics in three patients with CCD were observed using panoramic radiographs and X-ray CT images. The electromyogram of masseter muscle and temporal muscle was obtained. The informed consents for this research were obtained from the patients.Results: The morphologic characteristics of CCD patients by panoramic radiograph and CT were (a)the zygomatic arch was discontinuous with the hypoplastic zygomatic bone, (b)the ascending ramus of the mandible had parallel-sided borders, (c)the coronoid process pointed upwards and/or posteriorly and (d)the masseter muscle were less thick than in age-and sex-matched control subjects. The functional characteristics of CCD patients' masticator muscle, obtained from the surface electromyography, were (e)the masseter muscle had low response and the temporal muscle indicated strong response with bilateral chewing.Discussion : The discontinuity of zygomatic arch of the CCD patients was thought to cause the unsteadiness or low resistance to the masticatory load, because the masseter muscle originates from the zygomatic arch. These situation was considered to result the small size and hypofunction of the masseter muscle, mutual hyperfunction of the temporal muscle and the remarkable electromyographic pattern in the patients with CCD. As compensation for the hypofunction of the masseter muscle, the other masticatory muscles may develop a hypermasticatory function.