Druzinsky R E
Department of Anatomy and Cell Biology, University of Illinois at Chicago 60612, USA.
J Morphol. 1995 Oct;226(1):79-101. doi: 10.1002/jmor.1052260106.
Analysis of synchronously recorded cine-radiographs and electromyograms in two rodents (Aplodontia rufa and Marmota monax) demonstrates that jaw movements and muscle activities during incisal functions are distinctly different from those found during mastication. Movements during incisal biting are primarily along the midline, accompanied by symmetrical activity of the jaw adductor muscles. Most biting cycles do not end in contact between upper and lower incisors. When contact does occur, the lower incisors are dragged along the lingual surfaces of the upper incisors. Cropping, or tip-to-tip occlusion of upper and lower incisors, was not observed. Sharpening of the lower incisors, a behavior which may be unique to the Rodentia, was recorded in both A. rufa and M. monax. During sharpening, the lingual surface of the lower incisor is dragged across the tip of the upper incisor producing a lingual wear facet. Like incisal biting, sharpening movements are primarily confined to the midline, although there may be lateral movements in some sharpening cycles. Sharpening cycles are among the most rapid cyclic movements recorded in mammals, as the mean frequencies of sharpening are 11 cycles/s in A. rufa and 8 cycles/s in M. monax.
对两种啮齿动物（北美旱獭和北美土拨鼠）同步记录的电影X光片和肌电图分析表明，切牙功能期间的颌骨运动和肌肉活动与咀嚼期间明显不同。切牙咬合时的运动主要沿中线进行，伴有颌内收肌的对称活动。大多数咬合周期并不以上下切牙接触结束。当接触确实发生时，下切牙沿上切牙的舌面拖动。未观察到上下切牙的啃咬或尖对尖咬合。在北美旱獭和北美土拨鼠中均记录到下切牙的磨牙行为，这可能是啮齿动物特有的行为。在磨牙过程中，下切牙的舌面在上切牙的尖端拖动，产生舌面磨损面。与切牙咬合一样，磨牙运动主要局限于中线，尽管在一些磨牙周期中可能存在侧向运动。磨牙周期是哺乳动物记录到的最快的周期性运动之一，因为北美旱獭磨牙的平均频率为11次/秒，北美土拨鼠为8次/秒。
