Dental Clinic 2, Department of Prosthodontics, University of Erlangen-Nürnberg, Erlangen, Germany.
J Oral Rehabil. 2010 Mar;37(3):178-84. doi: 10.1111/j.1365-2842.2009.02036.x. Epub 2009 Dec 7.
Jaw muscle activity ratios in unilateral isometric biting differ from ratios of unilateral chewing but approach the latter if the jaw gape in biting is made as small as the minimum interocclusal distance (MID) of chewing. Especially, the masseter working/balancing side ratio (W/B-ratio) becomes as asymmetric as in chewing, because of reduction in balancing side (BS) masseter activity. This behaviour of ratios might reflect a 'chewing-specific' motor strategy induced when isometric biting is performed with a 'chewing-like' gape. If this hypothesis applies, activity ratios should be associated with MIDs of sequent chewing strokes in a similar manner as with incremented jaw gapes in isometric biting. To test this prediction, bilateral surface electromyograms of masseter and anterior temporalis muscles and incisor movements were recorded during unilateral chewing in 52 subjects. W/B-ratios of masseter and temporalis activities and temporalis/masseter-ratios on both sides were calculated. The ratios were related to MIDs of consecutive chewing cycles. Three of the four ratios were associated with masticatory MID in the same manner as with jaw gape in isometric biting. In particular with decreasing MID, the masseter W/B-ratio increased from 1.5 to 2.2 (P < 0.01). This increase in asymmetry was attributed to a stronger decrease in masseter activity on the BS than on the working side. We conclude that relative jaw muscle activation is associated with interocclusal distance in a similar way in isometric biting and in chewing. This analogy supports the idea of a common jaw gape-related neuromuscular strategy facilitated by afferent signalling of interocclusal distance.
在单侧等长咀嚼中，咀嚼肌活动比率与单侧咀嚼的比率不同，但如果在咬合力中使咬合间隙小到与咀嚼的最小牙合距（MID）一样，那么这些比率就会接近后者。特别是，由于平衡侧（BS）咬肌活动的减少，工作/平衡侧比率（W/B-ratio）变得与咀嚼一样不对称。这种比率的行为可能反映了一种“咀嚼特异性”的运动策略，这种策略是在进行“咀嚼样”开口的等长咬合时产生的。如果这个假设适用，那么活动比率应该与连续咀嚼运动的 MID 以类似于等长咬合中增加的颌间隙的方式相关联。为了验证这个预测，在 52 名受试者中记录了单侧咀嚼时双侧咬肌和前颞肌的表面肌电图和切牙运动。计算了咬肌和颞肌活动的 W/B-比值以及双侧的颞肌/咬肌比值。这些比率与连续咀嚼周期的 MID 相关。这四个比率中的三个与咀嚼的 MID 以与等长咬合中颌间隙相同的方式相关。特别是，随着 MID 的减小，从 1.5 到 2.2，（P < 0.01），W/B-比值增加。这种不对称的增加归因于 BS 上的咬肌活动比工作侧下降得更厉害。我们得出结论，相对的颌肌激活与等长咬合和咀嚼中的牙合距以相似的方式相关。这种相似性支持了一种共同的颌间隙相关神经肌肉策略的想法，这种策略是由牙合间隙的传入信号所促进的。
