Effect of functional appliances on jaw muscle activity.

The electromyographic (EMG) activity of masticatory muscles was monitored longitudinally with chronically implanted EMG electrodes to determine whether functional appliances produce a change in postural EMG activity of the muscles. Preappliance and postappliance EMG levels in four experimentals that had been fitted with functional appliances were compared against the background of EMG levels in controls without appliances. The insertion of two types of functional appliance to induce mandibular protrusion was associated with a decrease in postural EMG activity of the superior and inferior heads of the lateral pterygoid, superficial masseter, and anterior digastric muscles; the decrease in the first three muscles was statistically significant. This decreased postural EMG activity persisted for approximately 6 weeks, with a gradual return toward preappliance levels during a subsequent 6-week period of observation. Progressive mandibular advancement of 1.5 to 2 mm every 10 to 15 days did not prevent the decrease in postural EMG activity.

Jaw movement-related activity and reflexly induced changes in the lateral pterygoid muscle of the monkey Macaca fascicularis.

The muscle was exposed in 12 lightly anaesthetized monkeys so that electromyographic recordings could be made from the superior and inferior heads. The separately recorded activity in each head was initially examined in relation to activity recorded simultaneously in other jaw muscles or to jaw movements produced actively by the animals or passively induced by the experimenter. Subsequently, the reflex effects of stimuli applied to various oral-facial sites were examined. In general, the superior head was active in association with jaw-closing muscle activity and related movements produced by the animal whereas the inferior head was mainly active in jaw-opening. Both heads increased their activity with passively-induced jaw-opening movements, especially if the jaw-opening was combined with a horizontal deviation of the mandible. Both heads showed reflexly-induced excitation and silent periods as a result of stimuli applied to oral-facial sites, the most effective sites being palatal, lingual, labial and buccal mucosa and the teeth, stimulation of which, as well as stimuli applied to mandibular joint and cutaneous afferents, could also reflexly induce silent periods in both heads. The various effects may be related to mechanisms for protection and stabilization of the mandibular joint and masticatory muscles.