Gallo L M, Fushima K, Palla S
Clinic for Masticatory Disorders and Complete Dentures, Center for Oral Medicine, Dental and Maxillo-Facial Surgery, University of Zürich, Switzerland,
J Dent Res. 2000 Aug;79(8):1566-72. doi: 10.1177/00220345000790080701.
Condylar and incisor trajectories are often used for the study of mandibular movements. Condylar trajectories, however, depend on the location of the reference point and can be interpreted erroneously. In contrast, the helical axis analysis yields an unequivocal description of rigid body kinematics. The aim of this study was to analyze the mandibular helical axis during mastication. Seven subjects without signs and symptoms of craniomandibular disorders and with class I occlusion were recorded by means of the opto-electronic system Jaws-3D during unilateral mastication of bread cubes (2-cm side). The helical axis was computed every 14 ms with a rotation threshold of 1 . Parameters describing its spatial orientation and position relative to the condyles were calculated. The helical axis changed orientation and position more pronouncedly during the closing than during the opening phases of mastication. The orientation varied significantly from beginning to end of closing but not of opening, indicating less fluctuation of the helical axis on opening than on closing. Also, the distance dCP between helical axis and reference condylar point varied more significantly (p < 0.05) on the working than on the balancing side: On the working side, dCP decreased during both opening and closing, whereas on the balancing side, dCP increased only for closing. Furthermore, the helical axis pathway often showed a bowing ventrally to the balancing condyle, indicating that, during closing, the balancing condyle still translated backward while essentially only rotation occurred around the working condyle. Thus, the helical axis changed its position and orientation continuously during mastication.
髁突轨迹和切牙轨迹常用于下颌运动的研究。然而，髁突轨迹取决于参考点的位置，可能会被错误解读。相比之下，螺旋轴分析能对刚体运动学给出明确的描述。本研究的目的是分析咀嚼过程中的下颌螺旋轴。通过光电系统Jaws - 3D对7名无颅下颌疾病体征和症状且为I类咬合的受试者进行记录，记录其单侧咀嚼边长为2厘米的面包块时的情况。每14毫秒计算一次螺旋轴，旋转阈值为1°。计算描述其空间方向以及相对于髁突的位置的参数。在咀嚼的闭口阶段，螺旋轴的方向和位置变化比开口阶段更明显。闭口阶段从开始到结束，其方向变化显著，而开口阶段则不然，这表明螺旋轴在开口时的波动小于闭口时。此外，螺旋轴与参考髁突点之间的距离dCP在工作侧比平衡侧变化更显著（p < 0.05）：在工作侧，开口和闭口时dCP均减小，而在平衡侧，dCP仅在闭口时增加。此外，螺旋轴路径通常向平衡髁突腹侧呈弓形，这表明在闭口时，平衡髁突仍向后平移，而基本上仅围绕工作髁突发生旋转。因此，在咀嚼过程中，螺旋轴的位置和方向不断变化。
