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

目的：结合锁骨颅发育不良（CCD）的特点，探讨咀嚼肌各功能对口颌系统的影响，即咀嚼肌功能对下颌运动的影响、咀嚼肌功能的方向改变以及与咀嚼肌功能减退相关的形态学特征。方法：采用全景x线片和x线CT观察3例CCD患者的形态学特征。取咬肌和颞肌肌电图。本研究获得了患者的知情同意。结果：CCD患者的全景x线和CT形态学特征为(a)颧弓不连续，颧骨发育不全，(b)下颌骨升支平行边缘，(c)冠突向上和/或向后指向，(d)咬肌厚度小于年龄和性别匹配的对照组。面肌电图显示CCD患者咀嚼肌的功能特征为(e)咀嚼肌对双侧咀嚼反应低，颞肌反应强。讨论：由于咬肌起源于颧弓，CCD患者的颧弓不连续性被认为是导致咀嚼负荷不稳定或抵抗力低的原因。这些情况被认为是导致CCD患者咬肌体积小，功能减退，颞肌相互亢进，肌电图明显的原因。作为咬肌功能减退的补偿，其他咀嚼肌可能出现咀嚼功能亢进。

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.