An electromyographic study of mandibular position in response to changes in body position.

lrotrusion of the mandible, with the attached muscular mass of the tongue, aids in maintaining a patent upper airway. In contrast, passive retrusion of the mandible and tongue, when the body is in the semireclined or reclined position, could compromise the airway. For example, it has been postulated that one factor increasing the risk of sudden infant death syndrome is allowing an infant to sleep lying on its back.’ Posterior displacement of the mandible, tongue, and soft palate with possible airway obstruction is more likely with the infant in this position. Previous electromyographic studies indicate a substantial increase in the baseline myoelectric activity of the genioglossus muscle, the main protruder of the tongue, when a subject’s head is tilted from the anatomic position to the supine position.2 Sauerland and Mitchell2 have referred to the “tongue-safety” feature of the genioglossus muscle in precluding airway obstruction. Mandible-maxillae and condyle-mandibular fossa relationships are necessary for airway patency and important for the management of the dental patient in the semireclined to reclined position. These relationships are dependent on associated muscle response to altered body position. The primary protruders of the mandible that might accompany the genioglossus muscle in counteracting passive retrusion of this bony tissue complex are the medial and lateral pterygoid and the masseter muscles. Therefore, it was of interest to investigate whether or not these muscles also demonstrate fluctuations in levels of myoelectric activity due to positional head changes. Numerous investigators have documented the electromyographic activity patterns of masticatory muscles in response to various movements of the head and to changes in the position of the mandible.3-6 These studies, however, did not use the more specialized