Video imaging analysis of movements of the condyle articular disk and its control by the lateral pterygoid muscle activity and sesory information from the periodontal ligament in rabbits

本研究的目的是分析在咀嚼皮质区（CMA）重复电刺激诱导的虚拟咀嚼过程中，兔下颌髁突关节盘的运动。众所周知，刺激CMA的外侧部分会在受刺激皮质的对侧诱导研磨型有节奏的下颌运动。当我们刺激两侧的CMA时，可以通过盘的视频成像来比较盘在工作侧和平衡侧的运动。为了拍摄椎间盘的视频图像，在麻醉的兔子中切除了颞骨鳞状部分的乳突，它构成了上关节腔的顶部。用高速摄像机（120张图像/秒）在侧视图中记录椎间盘的运动。根据切牙的运动和咬肌的肌电活动，将一个咀嚼运动周期分为9个阶段。圆盘在一个周期内的运动被表示为一系列的9个圆盘的线图，这些线图是通过跟踪这些阶段的视频图像拍摄的。矢状面上的椎间盘运动轨迹远不是在斩波式颌运动中特别观察到的圆弧。在平衡侧和工作侧之间，盘运动的路径有很大的不同。椎间盘前后、背腹方向的活动范围约为3.5mm。工作侧最前方和最前方偏离椎间盘的绝对位置分别为相对于平衡侧后方和下方1 mm。盘的最前位置的时期与研究的髁突同侧咬肌的肌电图爆发活动的时期一致。结果表明，关节盘的运动在工作侧和平衡侧之间有很大的不同。

The purpose of the present study is to analyze the movements of the articular disk of the mandibular condyle of rabbits during fictive mastication induced by repetitive electrical stimulation of the masticatory cortical area (CMA). Stimulation of the lateral portion of the CMA is well known to induce grind type of rhythmical jaw movements on the side contralateral to the cortex stimulated. It would be possible to compare the movements of the disk on the working and balancing sides by means of video imaging of the disk, when we stimulated the CMAs on both sides. To take video images of the disk, the zygomatic process of squamous part of the temporal bone, which makes the roof of upper articular cavity, was removed in anesthetized rabbits. The movements of the disk were recorded with high-speed video camera (120 images/sec ) in lateral view. One masticatory cycle was divided into 9 stages on the bases of the incisor movements and the EMG activities of the masseter. The movements of the disk in a cycle were represented as a series of 9 line drawings of the disk That were taken by tracing the video images at these stages. The trajectories of the disk movements on the sagittal plane were far from circular arc that was particularly observed in the chopper type of jaw movements. The pathway of the disk movements were widely different between on the balancing and working sides. The range of the movements of the disk was about 3.5 mm in antero-posterior and dorso-ventral directions. Absolute positions of the anterior- and inferior-most deviated disk on the working side were as much as 1 mm posterior and inferior relative to those on the balancing side, respectively. The period of the anterior-most position of the disk was coincident with the period during which the EMG burst activities of the masseter muscle ipsilateral to the condyle studied was present. It was revealed that the movements of the articular disk are widely different between on the working and balancing sides.