MORPHOLOGICAL AND FUNCTIONAL ANALYSIS OF MASTICATOR MUSCLE WITH APPLICATION OF THE PATIENTS WITH CLEIDOCRANIAL DYSPLASIA

目的：本研究的目的是通过对锁骨颅骨发育不良（cleidocranial dysplasia，CCD）患者的研究，阐明口颌系统中各咀嚼肌的功能，即咀嚼肌功能对下颌运动的影响、咀嚼肌功能的代偿性变化以及与咀嚼肌功能减退相关的形态学特征。本文应用曲面断层片和X线CT图像观察了3例CCD的形态学特征。获取咬肌和颞肌肌电图。结果：CCD患者颧骨发育不良，颧弓不连续。下颌骨的升支有平行的边界。冠突细长，向上、向后突出。CCD患者咬肌最厚值小于对照组，未纳入均数±2SD范围。CCD患者双侧咀嚼时咬肌表面肌电反应低，颞肌表面肌电反应强。讨论：CCD患者颧弓不连续，导致咬肌不稳定，对肌肉收缩产生的负荷抵抗力不足。这些情况被认为是导致CCD患者咬肌体积小、功能低下、颞肌功能相互亢进和特征性肌电图模式的原因。颞肌功能亢进被认为是导致下颌骨形态异常的原因。

Purpose : The purpose in this research were to clarify the each masticator muscle function to the stomatognathic system, which were the effect of masseter muscle function to the mandibular movement, the compensational changes in masticator muscle function and the morphological characteristics associated to the hypofunction of the masseter muscle, with application of the patients with cleidocranial dysplasia (CCD).Method : The morphological 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 patients' consents were obtained for this research.Results : In the patients with CCD, the zygomatic bone was hypoplastic and the zygomatic arch was discontinuous. The ascending ramus of the mandible had pararell-sided borders. The shape of the coronoid process was slender and pointing upwards and posteriorly. The thickest values of the masseter muscle of CCD patients were smaller than that of the control subjects and were not included in the range of mean±2SD. In the patients with CCD, the surface electromyogram of 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 caused the unsteadiness of the masseter muscle and had not enough resistance to the load produced by the muscle contraction. These situation was considered to result the small size and hypofunction of the masseter muscle, mutual hyperfunction of the temporal muscle and the characteristic electromyogram pattern in the patients with CCD. The hyperfunction of the temporal muscle was considered to cause the abnormal shape of the mandibular bone.