Mandibular elevator muscles: physiology, action, and effect of dental occlusion
ABSTRACT In spite of differences in embryologic origin, central nervous organization, and muscle fiber distribution, the physiology and action of mandibular elevator muscles are comparable to those of skeletal muscles of the limbs, back, and shoulder. They also share the same age-, sex-, and activity-related variations of muscular strength. With respect to pathogenesis, the type of muscular performance associated with the development of fatigue, discomfort, and pain in mandibular elevators seems to be influenced by the dental occlusion. Clinical research comparing the extent of occlusal contact in patients and controls as well as epidemiologic studies have shown reduced occlusal support to be a risk factor in the development of craniomandibular disorders. In healthy subjects with full natural dentition, occlusal support in the intercuspal position generally amounts to 12–14 pairs of contacting teeth, with predominance of contact on first and second molars. The extent of occlusal contact clearly affects electric muscle activity, bite force, jaw movements, and masticatory efficiency. Neurophysiologic evidence of receptor activity and reflex interaction with the basic motor programs of craniomandibular muscles tends to indicate that the peripheral occlusal control of the elevator muscles is provided by feedback from periodontal pressoreceptors. With stable intercuspal support, especially from posterior teeth, elevator muscles are activated strongly during biting and chewing with a high degree of force and masticatory efficiency, and with relatively short contractions, allowing for pauses. These variables of muscle contraction seem, in general, to strengthen the muscles and prevent discomfort. Therefore, occlusal stability keeps the muscles fit, and enables the masticatory system to meet its functional demands.
- Journal of Biomechanics 02/1978; 11(8-9):389-95. · 2.72 Impact Factor
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ABSTRACT: Electromyograms (EMGs) of the temporal and masseter muscles in sixty patients with temporomandibular joint disturbance syndrome (TMJDS) and thirty controls were recorded and integrated on-line in the postural position and during maximum clenching, before and after occlusal splint therapy. Contrasting with the controls, the myoelectrical activity of the patients was higher in the postural position and lower during maximum clenching, whilst the former in percentage terms increased when compared to the latter. After treatment, the EMG indexes in some patients returned partially, and in others completely, to a normal level. Tenderness in the mandibular elevators, deviated opening and organic change in the TMJ increased the postural myoelectrical activity, in percentage terms, against that of maximum clenching. The myoelectrical activity of the mandibular elevators in the postural position and during maximum clenching was smaller in patients with the occlusal splint than in those without. The results show that the mandibular elevators in the patients with TMJDS were hyperactive and tense, and that the occlusal splint was useful for treating such dysfunction.Journal of Oral Rehabilitation 04/1989; 16(2):155-61. · 2.34 Impact Factor
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ABSTRACT: To elucidate the effects of food character on chewing patterns in humans, the electromyographic activity (EMG) of the chewing muscles and also the jaw movements were recorded in twenty-nine young subjects during ordinary chewing of five different foods. The results obtained were as follows. (a) The harder food materials showed a higher amplitude of the masseter EMG than the softer ones. (b) Concerning the number of chewing strokes and the elapse of time until the last swallowing action, subjects could be divided into two groups. (i) In the first major group, the number of chewing strokes and chewing time until the last swallowing action increased following increase of hardness of the food. This suggests that chewing force and chewing movements may be strongly influenced by the texture of food, especially its hardness. Further, the degree of pulverization of eating materials appears to be the major factor in controlling the swallowing action. (ii) In the second minor group, the chewing strokes and the chewing time were less influenced by the hardness of food. Here, a certain number of chewing strokes could be stimulating the swallowing centre in the brain and so induce swallowing, regardless of the degree of pulverization of the food.Journal of Oral Rehabilitation 04/1989; 16(2):177-83. · 2.34 Impact Factor