第三磨牙伸长者咀嚼运动轨迹的研究

目的：探讨对颌第二磨牙远中有密切接触的，伸长的第三磨牙对咀嚼运动轨迹的影响。方法：应用K6－I型下颌运动轨迹描记仪，分别记录11名第三磨牙伸长者和12名正常He者用左、右侧咀嚼口香糖的运动轨迹。结果：（1）正常He者冠状面和水平面咀嚼运动呈规则环形，He期轨迹明显，矢状面开闭口He期轨迹多数重合。（2）63．6％的第三磨牙伸长者冠状面He期轨迹出现内外向约0．2－1．0mm的平台，50％的水平面轨迹有前后向约0．2－0．5mm的台阶，72．7％的矢状面开闭口He期轨迹不重合，冠状面出现平台与矢状面不重合及水平面出现台阶的异常轨迹明显相关。（3）第三磨牙伸长者咀嚼运动中向后运动的幅度及咀嚼速度均明显增大。结论：第三磨牙伸长对咬合运动形式与咀嚼的幅度、速度有明显影响。

The effect of the hyper- erupted third molar on chewing movement

Objective To investigate the effect of the hyper-erupted third molar contacting closely t o the distal surface of the opposing second molar on the chewing movement. Methods Twenty-three university student volunteers, 11 with hyper -erupted third molar teeth and 12 with normal occlusion,were en rolled in present study. There were totally 6 unilateral hyper-erupted third m olars (3 upper and 3 lower) and 5 bilateral hyper-erupted third molars (1 bila teral upper and 4 bilateral lower). No other significantly abnormal occlusal p henomenon was ob served. Five gum-chewing cycles masticated with on each side were separately r ecorded by means of K6-I mandibular kinesiograph (MKG) and the chewing cycles were analyzed. Both three-dimensional amplitudes and the related velocities we re automatically documented with the instrument. Results (1) T he chewing graphs recorded on both frontal and horizontal planes in controls wer e typically smooth cycles with clearly occlusal phase tracings. On the sagital plane the openin g and closing traces around intercuspal position (ICP) were usually overlapped w ith each other. (2) 63.6% frontal cycles of the subjects with hyper-erupted t hird molar had an obvious table (0.2 mm to 1.0 mm in width) around ICP, 50% h or izontal cycles of the subjects had a 0.2 mm to 0.5 mm step near to ICP, 72.7 % ope ning and closing traces on the sagital plane separated into anterior and posteri or branches. The abnormal traces on the three different planes of the h yper-erupted third molar tooth group appeared to be related each other, implyin g that they might be caused by the same characteristics of occlusion, namely, th e hyper-erupted third molar. (3) Subjects with hyper-erupted third mola r masticated in more posterior direction, together with a higher chewing termina l velocity. Conclusions The hyper-erupted third molar had a s ignificant effect on the chewing cycles around ICP, as well as on the amplitude and velocity of chewing movement.