目的：探讨两种不对称咬合--单侧后牙反牙 合和单侧第三磨牙伸长，与正常牙 合者翼外肌磁共振影像形态的特点及规律，并从影像学角度探讨翼外肌上下头的功能。方法：分别具有上述3种咬合的受试者各10名，双侧翼外肌正矢状位MRI成像。结果：3组受试者的翼外肌上下头均表现为在大开口时缩短增粗的收缩影像，在牙尖交错位闭口和紧咬时的舒张影像。不对称咬合组双侧翼外肌在大开口状态下的影像与咬合引导的牙尖交错位偏斜有一定相关关系。结论：翼外肌上下头均在闭口时舒张、大开口时收缩；不对称咬合者双侧翼外肌开口位时的收缩活动明显不对称，且与异常咬合对牙尖交错位的引导有关。%Objective: To investigate the characteristics of magnetic resonance image of lateral pterygoid muscle in the people with normal occlusion and those with asymmetrical occlusion--unilateral posterior cross-bite or unilateral hyper-erupted third molar and to study the functions of superior and inferior heads of lateral pterygoid muscle. Methods: 30 volunteers, each 10 with one of the three types of occlusion, were adopted. Sagittal images of bilateral lateral pterygoid muscles with the mandible seated at intercuspal position with and without biting, and at mouth-open-position were taken respectively. Results: Both of superior and inferior lateral pterygoid muscles showed relaxation in-phase as the mouth closed at intercuspal position as well as bit at intercuspal position, and contracted in-phase when mouth opened. The images of lateral pterygoid muscles of those with asymmetrical occlusions showed significant asymmetrical appearances at mouth open position. Conclusion: Both of superior and inferior lateral pterygoid muscles relax in-phase as the mouth closes and as bites at intercuspal positions, and contract in-phase when mouth opens. The asymmetry action of lateral pterygoid muscles at opening in subjects with asymmetrical occlusion is related to their occlusions.
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