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PubMed1993

Effect of sympathetic nervous system activation on the tonic vibration reflex in rabbit jaw closing muscles.

1. In precollicular decerebrate rabbits we investigated the effect of sympathetic stimulation, at frequencies within the physiological range, on the tonic vibration reflex (TVR) elicited in jaw closing muscles by small amplitude vibrations applied to the mandible (15-50 microns, 150-180 Hz). The EMG activity was recorded bilaterally from masseter muscle and the force developed by the reflex was measured through an isometric transducer connected with the mandibular symphysis. 2. Unilateral stimulation of the peripheral stump of the cervical sympathetic by the TVR, and a marked decrease or disappearance of the ipsilateral EMG activity. No significant changes were detected in the EMG contralateral to the stimulated nerve. Bilateral CSN stimulation reduced by 60-90% the force reflexly produced by the jaw closing muscles and strongly decreased or suppressed EMG activity on both sides. This effect was often preceded by a transient TVR enhancement, very variable in amplitude and duration, which was concomitant with the modest increase in pulmonary ventilation induced by the sympathetic stimulation. 3. During bilateral CSN stimulation, an increase in the vibration amplitude by a factor of 1.5-2.5 was sufficient to restore the TVR reduced by sympathetic stimulation. 4. The depressant action exerted by sympathetic activation on the TVR is mediated by alpha-adrenergic receptors, since it was almost completely abolished by the I.V. administration of either phentolamine or prazosin, this last drug being a selective antagonist of alpha 1-adrenoceptors. The sympathetically induced decrease in the TVR was not mimicked by manoeuvres producing a large and sudden reduction or abolition of the blood flow to jaw muscles, such as unilateral or bilateral occlusion of the common carotid artery. 5. The effect of sympathetic stimulation was not significantly modified after denervation of the inferior dental arch and/or anaesthesia of the temporomandibular joint, i.e. after having reduced the afferent input from those receptors, potentially affected by CSN stimulation, which can elicit either a jaw opening reflex or a decrease in the activity of the jaw elevator muscle motoneurons. 6. These data suggest that, when the sympathetic nervous system is activated under physiological conditions, there is a marked depression of the stretch reflex which is independent of vasomotor changes and is probably due to a decrease in sensitivity of muscle spindle afferents.

Animals↗
PubMed1988

Influence of the activator on electromyographic activity of mandibular elevator muscles.

Integrated electromyographic (IEMG) activity was recorded in 15 children with Class II, Division 1 malocclusion undergoing treatment with an activator. EMG activity was recorded with surface electrodes from anterior temporal and masseter muscles, with and without the activator in the postural mandibular position, during saliva swallowing and maximal voluntary clenching. Similar IEMG activity in the postural mandibular position and during maximal voluntary clenching, with and without activator, was observed. During saliva swallowing, the activity in both muscles was significantly higher with the activator. This supports the rationale for diurnal wear of the activator. Simple linear regression analysis showed a significant negative correlation between the change of masseter muscular activity during saliva swallowing and age of the children (r = -0.51), suggesting that treatment with the activator should be started at an early age.

Activator Appliances↗
PubMed2001

Neuroendocrine, immune, and local responses related to temporomandibular disorders.

Orofacial pain frequently originates from pathologic conditions in the masticatory muscles or temporomandibular joints (TMJs). The mediators and mechanisms that monitor pain and inflammation, centrally or peripherally, are of great interest in the search for new treatment modalities. The neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), and neuropeptide Y (NPY) have all been found at high levels in the synovial fluid of arthritic TMJs in association with spontaneous pain, while serotonin (5-HT) has been found in association with hyperalgesia/allodynia of the TMJ. Interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF alpha) have been found in arthritic TMJs, but not in healthy TMJs, in association with hyperalgesia/allodynia of the TMJ as well as spontaneous pain. Anterior open bite, which may be a clinical sign of TMJ destruction, has been found in association with high levels of CGRP, NPY, and IL-1 beta in the synovial fluid of the TMJ. Interleukin-1 beta has also been related to radiographic signs of joint destruction. Prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) are both present in the arthritic TMJ, and PGE2 has been shown to be associated with hyperalgesia/allodynia of the TMJ. Very little is known about pain and inflammatory mediators in muscles. However, we know that 5-HT and PGE2 are involved in the development of pain and hyperalgesia/allodynia of the masseter muscle in patients with fibromyalgia, whereas local myalgia (myofascial pain) seems to be modulated by other, as yet unknown mediators. Interaction between the peripheral nervous system (sensory and sympathetic nerves), the immune system, and local cells is probably of great importance for the modulation of pain and inflammation in the TMJ and orofacial musculature.

Arthritis↗
PubMed1983

Reflex sensitivity of human jaw-closing muscles during the silent period following a jaw jerk.

Two successive force impulses were exerted upon the mandible in the opening direction with intervals of 20 to 120 ms. Electromyographic responses were recorded from the right temporal and masseter muscles and from the anterior belly of the right digastric muscle. Mandibular movement was recorded in the sagittal plane. The first-force impulse evoked a jaw jerk followed by a silent period. The jaw jerk following the second-force impulse was depressed when the interval between the force impulses was shorter than a certain value. The depression was total for at least 20 ms after the first jaw jerk. It is suggested that the silent period is the result of more than one inhibitory mechanism. From comparison of the resulting mandibular movement with movements resulting from single-force impulses, it is concluded that the jaw jerk may contribute to a small but significant extent to the stiffness of jaw-closing muscles.

Adult↗
PubMed1985

Masseteric muscle hypertrophy.

Three cases of masseteric muscle hypertrophy are reported. The clinical features of the syndrome are illustrated. The differential diagnosis of parotid mass, inflammatory or neoplastic, vs. masseter muscle hypertrophy is discussed. CT scanning is the best diagnostic tool. Expectant therapy is suggested.

Adolescent↗
PubMed1992

A muscle fatigue index based on the relationship between preceding background activity and myotatic reflex response (MRR).

A new index of muscular fatigue was developed using the myotatic reflex response (MRR). The MRR of masseter muscles is evoked by periodical mechanical chin tapping during clenching. The MRR waveform is composed of somewhat synchronized action potentials of muscle fibers. We estimate the change of the MRR waveform due to fatigue using the instantaneous frequency pattern (IFP) with the Hilbert transform. As a result, the features of IFP were different from the monotonic changes that have been observed by the conventional fatigue indices. That is, a plateau IFP was observed ahead of considerable fatigue, whereas the IFP showed a monopeak pattern during other phase of an exercise. Also, the relationship between the preceding background mean power frequency and the instantaneous frequency around the first part of the MRR waveform was nonlinear during the whole process of fatigue. These features may allow us to estimate the degree of fatigue at each time instant. Although the details have not yet been solved, by using the computer simulations one of them seemed to be the alteration of the dominant frequency components. The dominant frequency components may be related to the active muscle fiber types.

Action Potentials↗
PubMed1996

Twitch interpolation in the assessment of the maximum force-generating capacity of the jaw-closing muscles in man.

The method of twitch interpolation was employed to study the maximum potential bite forces of humans. Transcutaneous electrical stimuli were applied to parts of one or both masseter muscles in eight volunteers while they bit with a variable but controlled isometric force on a unidirectional force transducer held between the anterior teeth. In all participants the twitch force produced by a single 1-ms pulse, of 25 50 mA intensity, was inversely and linearly related to the voluntary bite force. For each participant the slope of the regression between twitch force and bite force depended on the stimulus intensity and not on whether the stimulus was applied to one or both masseters. Extrapolation of the regression lines to zero twitch force showed that they converged towards a bite-force value that, for any given participant varied only a small amount between different stimulus intensities. For most participants this bite force lay above the maximum that they produced voluntarily: voluntary maximum bites ranged from 153 to 593 N, while the extrapolations predicted a narrower and higher potential range of 282-629 N. It was concluded that, for the masseters at least, there is often spare force-generating capacity which individuals are either unable or not prepared to utilize. This method is non-invasive and may help to define better the maximum bite-force potential of humans.

Adult↗
PubMed1986

Distribution of muscle activity during sleep in bruxism.

10 outpatients with bruxism were investigated by polygraphic recordings during night sleep. Electromyogram, electrooculogram and electroencephalogram derivations were used to evaluate the activities of masseter muscle and the different stages of sleep. The results of the bruxist group were compared to those of an age-matched control group. The amount and the length of pressing and grinding jaw movements were correlated with the sleep period time as well as with the different sleep stages. In comparison to the control group, a significant difference of muscle activity longer than 5 s was found, but there was no difference regarding activities of 3-5 s duration. The highest level of activity was found in sleep stage two and during awakening times. No difference was seen with regard to percentages of the sleep stages.

Adult↗
PubMed1994

A quantitative histochemical study of the spatial distribution of intrafascicular fibre types in the porcine masseter and soleus muscles.

The distribution of intrafascicular type I and II muscle fibres together with proportions of edge- and centrally located type I and II fibres within whole fascicles were analysed by myosin ATP-ase histochemistry in 241 porcine masseter fascicles (six masseter muscles) and compared with result from 63 pig soleus fascicles (five soleus muscles). All fascicles were from 11 domestic pigs (1 yr old, 70-90 kg body weight, all female). The proportions of type I fibres (slow) and type II fibres (fast) on the edge of fascicles differed significantly from the proportions centrally. All the soleus fascicles had higher proportions of centrally located type I fibres. Only seven out of 241 (3%) masseter fascicles diverged in this respect and showed reversed intrafascicular fibre-type proportions with more edge-located type I fibres. Analysis of the fascicular distribution of type I and II fibres revealed that the porcine masseter had type II fibres as the predominant type. Between 68-87% of the total fibres were type II (p < 0.001). The intrafascicular content of type I fibres increased towards the deep part of the masseter. In four of five soleus muscles the type II fibre population was dominant (p < 0.01). However, one soleus revealed equal proportions of type I and II fibres.

Animals↗
PubMed2000

The relationship between dentofacial morphology and the isometric jaw-opening and closing muscle function as evaluated by electromyography.

The purpose of this study was to clarify the relationship between the dentofacial morphology and masticatory muscle function in both isometric jaw-opening and closing. The subjects consisted of 26 male adults without masticatory dysfunction. Electromyograms were obtained from the digastric and masseter muscles to evaluate their muscle activities. The sum energy, median frequency, and equilibrium index were calculated as parameters of the muscle activity. A correlation analysis was performed between the parameters for the muscle activity and the dentofacial morphology on lateral roentgenographic cephalograms. The sum energy in the jaw-closing muscle showed a significant relationship with the gonial angle, mandibular length, and facial height, but not in the jaw-opening muscle. A median frequency in the jaw-opening muscle showed a significant relationship with size and position of the mandible, and also that in the jaw-closing muscle with the mandibular plane angle, facial height, and mandibular body length. Furthermore, the equilibrium index of the median frequency was related to the facial height, mandibular length, and inclination of the mandibular incisor. In conclusion, the dentofacial morphology was found to be closely related to the muscle activity not only of the jaw-closing muscle but also of the jaw-opening muscle during isometric muscle contraction.

Adult↗
PubMed1999

The study of jaw reflexes evoked by electrical stimulation of the lip: the importance of stimulus intensity and polarity.

The aim of this study was to investigate whether reported differences in the patterns of jaw reflexes which can be evoked by electrical stimulation of the lip might be related to the intensity or polarity of the stimuli. Constant-current stimuli were applied through bipolar electrodes clipped across the lower lip of 14 subjects while EMG recordings were made from a masseter muscle. During stimulation, the subjects sustained a level of masseter activity equivalent to 10% of their maximum. The stimuli were applied as multiples of sensory threshold. The EMGs were analysed following rectification, averaging and smoothing. A sequence of inhibitory, excitatory, inhibitory and excitatory responses could be produced in the muscle by both polarities of stimuli. The latencies of these four responses were generally in the ranges 10-20, 25-40, 40-55 and 80-100 ms, respectively. These latencies, particularly for the last two responses, tended to decrease at higher intensities of stimulation. The threshold for the long-latency inhibition was significantly lower than that for the short-latency inhibition when the cathode was outside the mouth but not when it was inside the mouth. In addition, the long-latency excitation had the lowest threshold of the four responses regardless of stimulus polarity. Since nerves are excited particularly around a cathode, we interpret these results as showing that stimulation of nerves supplying the skin outside the mouth evokes predominately long-latency jaw reflexes whereas shorter latency responses can be evoked by stimulating nerves supplying oral mucosa. Furthermore, long latency excitatory reflexes seem to be the most easily evoked by stimulation of the lip.

Adult↗
PubMed1998

[Electromyographic power spectral analysis of sternocleidomastoid muscle during sustained voluntary clenching].

The purpose of this study was to investigate the changes of the activity of the sternocleidomastoid (SCM) muscles during sustained voluntary clenching. Ten healthy male subjects without any occlusal functional problems were asked to clench as long as possible in the intercuspal position while keeping the electromyographic activity of the masseter muscle at the 50% maximum voluntary contraction. Frequency analysis was carried out by computer using a fast Fourier transform algorithm to obtain the power spectrum of the SCM muscle during the fatiguing process and the recovery process. The results were as follows: 1. Sustained activities of the SCM muscles were observed during sustained voluntary clenching. 2. The power spectra of the SCM muscles significantly shifted to a lower frequency as time elapsed. 3. The power spectra of the SCM muscles obtained three minutes after relaxation recovered to those of the beginning of clenching. These findings indicated that muscle fatigue may be induced in the SCM muscle during sustained voluntary clenching and that electromyographic power spectral analysis can be used as a noninvasive, objective, and quantitative index of SCM muscle fatigue.

Adult↗
PubMed2006

Effects of clenbuterol and cyclosporin A on the myosin heavy chain mRNA level and the muscle mass in rat masseter.

To gain more insight into the molecular mechanism of muscle growth and fiber-type transformations, we analyzed the effects of beta(2)-adrenergic agonist clenbuterol (CB) and/or cyclosporin A (CsA), a potent inhibitor of calcineurin (CaN), on the muscle mass as well as on the mRNA levels of myosin heavy chains (MHC I, IIa, IId/x, IIb), using a real-time RT-PCR with specific primers in rat masseter. In comparison with control, the CB treatment significantly decreased the MHC I mRNA level (p < 0.01), but increased the MHC IId/x mRNA level (p < 0.01), and the CsA treatment significantly decreased the MHC I mRNA level (p < 0.05) in association with the significant decrease in MHC IIb mRNA level (p < 0.05). The CB+CsA treatment significantly decreased the levels of MHC I (p < 0.01) and IIa mRNAs (p < 0.05), but increased the MHC IId/x mRNA level (p < 0.001) in association with a significant decrease in MHC IIb mRNA level (p < 0.01), in comparison with control. The masseter muscle mass was significantly (p < 0.001) increased by either the CB or the CB + CsA treatment, but decreased with the CsA treatment (p < 0.01). These results suggest that in rat masseter muscle, CB has an anabolic action accompanying MHC mRNA I IIa IId/x sequence transition independently of CaN-signaling pathways, and CaN is involved in the type I fiber gene expression and the muscle mass maintenance of type IIb fiber.

Adrenergic beta-Agonists↗
PubMed2000

[Muscular equilibrium and orthognathic surgery. A preliminary electromyographic study].

Few studies have been written about the effects of orthodontic preparation and of the consequences of surgical movements on mandibular motricity. The aim of this preliminary report is to evaluate the modifications of muscular activity between the pre-surgical phase and its evolution during the year after surgery, together with the skeletal modifications found. The muscular activity of six patients with serious vertical discrepancies requiring rehabilitation of the lower facial height has been studied using electromyographical recordings. A longitudinal study of the EMG data has been established in order to discover a muscular adaptation method towards physiological equilibrium following the realization of a new facial diagram. The reduction of the lower facial height obtained through a surgical procedure including a maxillary impaction, appears to indicate that, at rest, the masseter muscles activity tends to normalize, whereas that of the temporal muscles may sometimes increase. During maximal contraction, facial hyper-divergence reduction would lead to a sharp decrease in temporal and masseter muscular activity which would subsequently return to normal. The increase in vertical dimension would also cause significant changes in muscular tonus depending on the sagittal direction of the associated mandibular osteotomy. It would take longer to achieve muscular activity stability. These few results show: The existence of significant modifications following orthognathic surgery, possible reduction of high rest muscular activities, often revealing a cranio mandibular dysfunction, after vertical typology rehabilitation. The electromyographic recordings during treatment then enable to perfect the therapeutic re-evaluation of these major vertical discrepancies.

Adaptation, Physiological↗
PubMed2005

[The influence of botulinum toxin on the masticatory muscles of the temporomandibular joint osteoarthritis in rabbit].

PURPOSE: To study the influence of botulinum toxin on masticatory muscle activity in temporomandibular joint model osteoarthritis(TMJOA). METHODS: 30 adult rabbits were examined with EMG, and TMJOA was established by collagenase injection, then divided into experimental group and control group. EMG of masticatory muscles was recorded during postural position and clenching at the end of 4 weeks, 8 weeks and 12 weeks. Botulinum toxin was injected into the masseter muscle and temporal muscle in the experimental group. Those of the control group were only with TMJOA. All data were analyzed with group t test in SPSS 11.0. RESULTS: During postural position, EMG activity of masticatory muscles in the control group was significantly higher than that of the normal at each examination(P<0.05). EMG activity in th experimental group was lower than normal at the end of 4 weeks and 8 weeks(P<0.05), but at the end of 12 weeks, the two groups showed no difference(P>0.05). During clenching, EMG activity in the control group was lower than normal at each measurement(P<0.05), EMG activity in the experimental group was lower than normal at the end of 4 weeks and 8 weeks(P<0.05), but showed no difference at the end of 12 weeks. CONCLUSION: Botulinum toxin can change and improve masticatory muscle function of TMJOA in rabbit.

Animals↗
PubMed2006

Isolated high-frequency jaw tremor relieved by botulinum toxin injections.

Jaw tremor can be seen as a component of various neurological disorders such as essential tremor, Parkinson's disease, dystonia, branchial myoclonus, hereditary geniospasm, task-specific tremor, and Whipple's disease, as well as in normal situations such as shivering, and subclinical physiological jaw tremor. In most of these conditions, the jaw tremor is usually associated with tremor or other abnormal involuntary movements affecting additional body parts, and its frequency is lower than 12 Hz. Schrag and colleagues reported a patient with a high-frequency idiopathic jaw tremor, and they speculated it could be related to orthostatic tremor affecting the masseter muscles. We encountered a similar patient with intermittent rapid focal jaw tremor that was successfully treated with botulinum toxin injections to the masseters.

Adult↗
PubMed1981

Electroconvulsive therapy: a comparison of seizure duration as monitored with electroencephalograph and electromyograph.

EEG and EMG were monitored simultaneously at 72 ECT sessions in 18 patients. When EMG was recorded from the leg the duration of EMG curve convulsions varied between 43 and 89% of the EEG recorded seizure duration of the same fit. The EMG/EEG seizure ratio varied widely among different patients as well as within the single patient during a series of ECT sessions. EMG recording from the masseter muscles showed EMG seizure duration to be more in accordance with the EEG seizure duration than EMG recordings from the leg. The EMG/EEG seizure ratio (masseter) varied from 65 to 100%, which was significantly higher than the EMG/EEG seizure ratio obtained with EMG recorded from the calf muscles. The use of EEG monitoring of ECT is advocated in order to obtain the most precise evaluation of the cerebral seizure activity. If EEG monitoring is not available EMG recorded from the masseter muscles provides a reasonably accurate and easily applicable method of monitoring the presence and duration of the ECT-induced seizure.

Depressive Disorder↗
PubMed1988

Surgery on the buccal fat pad in masseter transfer.

The buccal fat pad is an essential anatomic structure in the esthetic presentation of the face. It may become hypertrophied, with fullness of the cheek, or atrophic, with a sunken appearance, or become a plus or minus factor in reconstruction in this area. Lipoma of this pad is extremely rare, but it must also be differentiated. There are, therefore, certain circumstances where the presence or absence of the buccal fat pad can create a specific imbalance and asymmetry in the face. The correction of these conditions may require reduction or augmentation. The anatomy, the risks, the classification, and the various surgical techniques that are available to accomplish this are outlined and correlated to the masseter muscle transfer.

Adipose Tissue↗