Masseter EMG Research Articles

Placebo effects in biofeedback and self-perception of muscle tension.

ABSTRACTThis study evaluated the effectiveness of laryngeal muscle biofeedback, a common treatment for subvocalization, utilizing a strict control group structure. Subjects were 29 undergraduates assigned to Laryngeal Feedback (N = 10), Masseter Feedback (N = 10), or No Feedback Control (N = 9) conditions. The results indicated that laryngeal muscle biofeedback had no specific treatment effect; however, masseter biofeedback demonstrated a specific treatment effect when the new procedure was utilized. Subjects in the Masseter Feedback Group displayed masseter EMG levels which were substantially lower than subjects in the Laryngeal Feedback Group (p<.05). In order to validate the results of the biofeedback control procedure, accuracy of myogenic perception was also tested, and found to be significant for the masseter (p<.001) but not for the laryngeal muscle. It is shown that the biofeedback control procedure can more accurately assess the presence or absence of specific treatment effects in biofeedback. Theoretical implications of the myogenic perception concept are discussed, and suggestions for future research in biofeedback and myogenic perception are provided.

Masseteric silent periods electrically evoked in normal subjects and patients with temporomandibular joint dysfunction

The mean latency and duration of electromyographic silent periods were compared in normal subjects and patients with symptoms of temporomandibular joint (TMJ) dysfunction. The silent periods were evoked in the masseter muscle by electrical stimulation of the mental nerve area and recorded at 100% and 50% of maximum masseter EMG activity. Two silent periods were typically observed. The mean latency of the early silent period as well as the mean duration of both the early and late silent periods were shorter at 100% than at 50% of the maximal voluntary activity. In comparing the two groups, the mean latencies were shorter and the mean durations were longer for both silent periods in the TMJ group compared with the normal group. The prolonged silent periods in the TMJ group do not appear to be caused by a difference in stimulus intensity or level of voluntary activity in the masseter muscle. These results permit the speculation that the mechanism of the prolonged silent period in the TMJ patients might be central rather than peripheral.

Relationship of masseter electromyographic activity to mandible position in the freely-moving rat

Simultaneous records of masseter-EMG activity and position of the mandible were made on 4 Wistar rats eating four food types: standard food pellets (large pellets), 45 mg precision food pellets (small pellets), bread and pudding. Masseter activity was recorded with chronic bipolar silver EMG electrodes placed within the muscle and led subcutaneously to a pedestal on the head. The transducer indicating jaw position consisted of two tiny inductance coils, placed on the head and under the mandibular symphysis. The lower coil acted as a receiving aerial for the carrier signal supplied via the upper coil, so that distance between the coils, and thus relative jaw position, was traced on the oscilloscope screen. A silent period was found in the masseter-EMG bursts similar to that found in man, where the silent period represents tooth contact and the occlusal phase of chewing (time during which teeth are in the intercuspal position) is defined as the interval between the silent period and the termination of the EMG activity in the muscle. Applying this to the rat data, opening represented 70–75 per cent of the total cycle while the combined closing and occlusion phases comprized 25–30 per cent when either type of pellet was eaten. With bread, closing and occlusal phases represented 56 per cent of the total cycle. For all three food types, muscular force, as indicated by the jaw-closing movement registered by the transducer, continued beyond the masseter EMG. Irregular jaw movements seen when the animals lapped pudding were not correlated directly with masseter activity.

Effect of bite force on the masseteric electromyographic silent period in man

The duration of the masseteric EMG silent period as induced by tapping on the chin was measured at different levels of sustained bite force. Under both open bite and normal occlusion, the duration of the silent period was inversely related to the magnitude of the bite force. For bite force of the same magnitude, the value of the silent period remained relatively constant for the same subject in different trials (SEM ≅ 1 per cent), whereas the absolute values of the silent periods ranged far and wide for different individuals even under similar experimental conditions.

Quiet period of masseter EMG induced by the mechanical tap during various levels of isometric contraction.

Quiet period of masseter EMG induced by the mechanical tap during various levels of isometric contraction.

Sensation and responses elicited by electrical stimulation of human tooth pulp

Quality of sensation elicited by electrical tooth pulp stimulation, and the correlation between the evoked EEG, and inhibition of the masseteric EMG, on the one hand, and the elicited sensation, on the other, were studied in respect to human subjects, and the following results were obtained.(1) Pre-pain was a sensation elicited by tooth pulp stimulation at a low intensity, while stimulation at higher intensities produced pain. These two sensations could be differentiated by the absence or presence of spatio-temporal summation, and their positive correlation with the early or late components of the evoked EEG as well as their threshold stimulus-intensities. Thus, it suggests that different mechanisms would be involved in the production of the two sensations.(2) The threshold intensity for pre-pain was approximately equivalent to that for an early component of the evoked EEG and an early phase of masseteric inhibition. In the range of stimulus-intensity for pre-pain, it showed a high positive linear correlation to the amplitude of an early component of the evoked EEG.On the other hand, in the range for pain, the stimulus intensity was more correlated to the late component than the early one. Therefore, it can be assumed that the evoked responses in cortical EEG and inhibition of the masseteric EMG to an electrical tooth pulp stimulation could be objective indices of the sensations elicited by tooth pulp stimulation.

Electromyographic Correlates of Experimentally Induced Stress in Diurnal Bruxists and Normals

Diurnal bruxists and normals were compared in responsiveness to stress and on psychological status. Results indicated that masseter EMG activity was significantly higher at rest for bruxists than normals, that bruxists responded differentially more to stress than normals, and that no significant differences were present between bruxists and normals on the psychological measures.

Effect of Placement of Electrodes and Inter-Electrode Resistance on Masseter EMG

Effect of Placement of Electrodes and Inter-Electrode Resistance on Masseter EMG

Jaw reflexes and masseter electromyograms in mesencephalic and pontine lesions: an electrodiagnostic study.

Jaw reflexes and masseter electromyograms were studied in five patients with mesencephalic and 11 patients with pontine lesions, vascular or tumorous in nature. In the former group jaw reflexes were abnormal, being delayed or absent, whereas masseter electromyograms were normal. In the latter group, both jaw reflexes and masseter EMG, showing denervation, were abnormal in six and both normal in five cases. It is suggested that the afferent limb of the human jaw reflex passes through the mesencephalic trigeminal nucleus. The methods proved to be valuable in the diagnosis of mesencephalic and pontine lesions involving the fifth cranial nerve.

Muscle afferents of trigeminal mesencephalic tract nucleus and mastication in chronic monkeys.

The nature of masticatory movement and related muscle spindle afferent activity was studied on awake monkeys. The pressure acting on the molar surface of the tooth and masseter EMG may develop in two phases, i. e. an early jaw movement and a late biting. Out of 20 identified spindle afferents, 10 units in ten monkeys showed a rate increase during jaw-muscle closing and the remaining 10 units showed a decrease of the rate. Although there were two phases to the masseter contraction, no correlation was found between the two phases and the spindle afferent discharge pattern. It was concluded that during voluntary jaw closing the fusimotor activation occurred simultaneously with masseter muscle activation.

Modification of cortically evoked rhythmic chewing and swallowing from midbrain and pons.

In rabbits under light ether anesthesia, the midbrain and upper pons were explored with tetanic stimuli to alter cortically evoked rhythmic chewing and swallowing. The effects of various surgical sections of the brain stem upon these phenomena were also studied.1. Stimulation in an extensive midbrain area produced a diminution of rhythmic chewing, and very often a complete arrest in the jaw-opened position, whereas that at two discretely localized areas produced an enhancement. Bilateral masseteric EMGs revealed a response comparable to the above, i. e., the activity decreased symmetrically during diminution, and accelerated during enhancement of rhythmic chewing. During the stimulation, elicitation of swallowing was consistently diminished without regard to changes occurring in rhythmic chewing.2. Stimulation at the upper pons produced an arrest of rhythmic chewing, with the jaw closed. At the same time the masseteric EMG was tetanically activated ipsilaterally, while being quiescent contralaterally. Another area delimited within or near the preceding one was responsible for a conspicuously long-lasting bout of repetitive swallowing.3. Longitudinal midline splits extending from the corpus callosum to the rostral border of the superior colliculi had no effect upon cortically evoked rhythmic chewing and swallowing or upon changes in those induced by brain stem stimulation. A short longitudinal cut at the superior colliculi largely eliminated the effect of enhancement, leaving that of diminution or arrest of cortically evoked rhythmic chewing. A similar split involving the lower midbrain and upper pons completely abolished cortically evoked rhythmic chewing. None of these midline splits, however, abolished swallowing, although it was reduced.4. Transverse hemisection just rostral to the superior colliculus eliminated cortically evoked responses ipsilaterally, leaving them intact contralaterally, whereas midpontine hemisections did not alter the responses.5. After complete decerebration at the supracollicular level the cortically evoked response was abolished but the irregular chewing and swallowing persisted with brain stemst imulation. Mid-pontine transection abolished such brain stem-elicited chewing and swallowing, leaving reflex swallowing intact.6. On the basis of these findings the neural control of rhythmic chewing and swallowing is discussed in relation to the reticular activating and inhibiting systems, and its probable arrangement is tentatively proposed.

A silent period in the masseter electromyogram following tooth contact in subjects wearing full dentures

A silent period in the masseter EMG has previously been observed following tooth contact in man. This has usually been attributed to inhibition of the muscle arising from stimulation of periodontal mechanoreceptors. Investigation of the masseter EMG of edentulous subjects wearing full dentures has shown that the changes in muscle activity that follow tooth contact are similar to those of subjects with natural teeth. These experiments provide evidence that the silent period does not necessarily depend upon stimulation of periodontal mechanoreceptors.

Two types of motor pause in masticatory muscles.

Two types of motor pause in masticatory muscles.