Effects of clenching on regulatory function of bite force in man-role of peridontal mechanoreceptor

据报道，磨牙症是导致颞下颌关节功能障碍的重要原因之一。关于肌肉活动和磨牙症之间的关系，已经进行了各种讨论。根据静息肌电活动的结果，提出了一种否定的观点，即颞颌功能障碍患者的疼痛与咀嚼肌过度活动之间存在因果关系。然而，最根本的问题并未阐明咬合对咀嚼系统的影响。我们已经调查了作为磨牙症的一种形式的咬合是否会在短期内对口腔颌面系统产生影响。像Hutton等人的实验一样，条件性咬合在没有力的视觉反馈的情况下，在复制学习的标准咬合力时导致了显著的误差。这些发现表明，紧握后可能发生了闭合肌肉运动神经元的易化。此外，我们还研究了咬合后牙周力的变化是否与牙周机械力有关。获得了以下结果。1.机械刺激器刺激上颌中切牙，最大咬合力为5%。短潜伏期抑制反应在咬肌中被诱导，其次是对牙齿轻敲的兴奋反应，而兴奋反应主要被诱导为缓慢的推动。2.受刺激的牙齿周围局部麻醉后，上述反应几乎消失。3.慢推刺激的兴奋性反应随背景放电水平的增加而增强。4.握紧25%M.V.C.-60秒前后，对慢推的反应没有明显变化。因此，虽然从牙周机械感受器到咬肌运动神经元的反射弧对咬合后效应的作用相对较小，但它显然对减缓推力有促进作用。

It has previously been reported that bruxism is noted as one of the important causes of a temporomandibular dysfunction. Various discussions have been done about a relation between muscular activity and bruxism. A negative view is proposed from the result of the resting EMG activity about a causal relationship between the pain and the hyperactivity of the masticatory muscle in patients with tempolomandibular dysfunction. However, the fundamental problem is not clarified how any influence the sutained clenching exerts to the masticatory system. We have investigated whether the clenching that is one of the form of bruxism influence for short term to the stomatognathic system. The conditioning clenching induced a significant error in reproducing a leamed criterion bite force under conditions of no visual feed-back of force, like the experiments of Hutton et al. These findings indicate the possibility that the facilitation of motoneurones of closing muscles might occur after clenching. Furthermore, we have investigated whether the periodontal mechanoreceopors are responsible for the effect after clenching. Following results were obtained. 1. The upper oentral incisors were stimulated by the mechanical stimulator under 5% maximum voluntary teeth clenching. A short-latency inhibitory response was induced in masseter muscle, followed by an exciatory response to brisk taps on the teeth, and mainly excitatory response was induced to slow pushes. 2. These responses were almost abolished by local anesthesia around the teeth stimulated. 3. An excitability response to slow pushes increased with background discharge level. 4. A significant change was not observed for response to slow pushes before and after the clenching for 25% m.v.c.-60 seconds. Consequently, although a reflex arc from the periodontal mechanoreceptor to the masseter motoneurone has relatively little role to the postclenching effect, it is obvious to have a facilitatory effect to slow pushes.