Jaw Muscle Orientation and Moment Arms of Long-face and Normal Adults
Jaw Muscle Orientation and Moment Arms of Long-face and Normal Adults
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DOI：
10.1177/00220345960750060801
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发表时间：
1996-06
影响因子：
7.6
通讯作者：
P. van Spronsen;W. Weijs;EC van Ginkel;B. Prahl-Andersen
中科院分区：
文献类型：
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作者：
P. van Spronsen;W. Weijs;EC van Ginkel;B. Prahl-Andersen
相对于正常人，长脸的受试者咬合力大大降低。这种差异不能完全用下颌肌肉横截面积的减少来解释。在这项研究中，我们调查是否正常和长脸受试者的下颌肌肉的方向和力矩臂是不同的，如果是这样，在何种程度上这些差异有助于观察到的最大磨牙咬合力水平的差异。对30例正常人和13例长脸人的颌部肌肉进行了三组不同方位的MRI扫描。这些作为计算机重建肌肉外部形状的基础。下颌肌肉的空间方向由通过肌肉横截面质心的回归线定义。下颌第一磨牙的咬合点和下颌肌肉的力矩臂相对于同侧髁状突的中心进行测量。肌肉变量，包括角度，力矩臂，和机械臂进行了分析，判别分析和多变量方差分析（MANOVA）。颞肌和二腹肌前肌的空间方向的差异对正常组和长脸组的区别贡献最大。与MANOVA，它表明，正常和长脸组没有显着差异方面的下颌肌肉力矩臂和机械优势的数据。两组的咬肌和二腹肌前肌矢状肌角只有很小的差异。在正常组和长脸组中，左右两侧肌肉的方向和力臂数据差异显著。得出的结论是，颌骨肌肉的空间方向的变化是小的，并没有显着的贡献，解释不同的磨牙咬合力水平的长脸和正常的科目。因此，很容易假设正常和长脸受试者的下颌肌肉在每单位横截面积上可以施加的最大力方面是不同的。
Long-face subjects have strongly reduced bite forces relative to normal subjects. This difference cannot be fully explained by the reduced cross-sectional area of the jaw muscles. In this study, we investigated whether the orientation and moment arms of the jaw muscles of normal and long-face subjects are different, and if so, to what extent these differences contribute to the observed differences in maximum molar bite-force levels. Three MRI scan series with different orientations were made of the jaw muscles of 30 normal and 13 long-face subjects. These served as the basis for computer reconstructions of the external shape of the muscles. The spatial orientation of the jaw muscles was defined by the regression line through the centroids of the muscular cross-sections. The moment arms of the jaw muscles and the bite point of the first mandibular molar were measured with respect to the center of the ipsilateral condyle. The muscular variables-including angles, moment arms, and mechanical advantage-were analyzed with a discriminant analysis and a multivariate analysis of variance (MANOVA). Differences in the spatial orientation of the temporalis muscle and the anterior digastric muscle contributed most to the distinction of the normal and long-face group. With MANOVA, it was shown that the normal and long-face group did not significantly differ with respect to the jaw muscle moment arms and mechanical advantage data. Only small differences were found between the sagittal muscle angles of the masseter and anterior digastric muscles in the two groups. In both the normal and long-face group, the orientation and moment arm data of the right and left muscles differed significantly. It was concluded that the variation of the spatial orientation of the jaw muscles is small and does not significantly contribute to the explanation of the different molar bite-force levels of long-face and normal subjects. Therefore, it is tempting to assume that the jaw muscles of normal and long-face subjects are different with respect to the maximum force they can exert per unit of cross-sectional area.