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PubMed1976

The reproducibility of electromyographic recordings of the masseter muscle in humans.

An investigation was undertaken into the reproducibility of electromyograms of masseter muscles in five human subjects. Under standardized conditions, integrated electromyographic recordings were taken during three sessions on each of 5 days. Analysis of variance showed that at the 0-05 probability level the results were reproducible for each subject not only during the same day but also between days.

Adolescent↗
PubMed1989

An HRP study of the central projections from primary sensory neurons innervating the rat masseter muscle.

Retrograde and transganglionic transport of horseradish peroxidase has been used to study the cell bodies of origin and the central projections of neurons innervating the rat masseter muscle. Labeled cell bodies were observed both in the trigeminal ganglion and in the mesencephalic trigeminal nucleus. Major central projections from mesencephalic trigeminal neurons were traced to the supratrigeminal nucleus and to the brainstem reticular formation. Smaller projections from these neurons could be followed to the borders of the solitary tract and hypoglossal nuclei as well as to lamina V of nucleus caudalis and corresponding areas in the dorsal horn at C1-C2 spinal cord segments. Labeling from trigeminal ganglion neurons was observed close to the trigeminal tract in all subdivisions of the trigeminal sensory nuclear complex and in the dorsal horn lamina I at C1 and C2 levels.

Animals↗
PubMed2000

Quantitative analysis of reflex inhibition in single motor units in human masseter muscle: effects of stimulus intensity.

Inhibitory reflex responses to electrical stimulation of the mental nerve were studied in recordings from single motor units (SMU) in the human masseter muscle. A new analytical technique for spike train data was used. Electrical stimuli were delivered to the mental nerve when the SMU fired with two consecutive inter-spike intervals (ISIs) within the range of 90 ms to 110 ms. Stimuli were delivered with increasing stimulus delays after the preceding SMU action potential (AP). Sham, non-painful, and painful stimulus intensities were applied. The post-stimulus firing probability of the SMU was progressively decreased among the three conditions. Analysis of the relation between stimulus delays and ISI for the first post-stimulus APs revealed a linear relation which was shifted upward, and the slope was increased with increasing stimulus intensity. This may be explained by a differential effect of the increasing stimulus intensity on the duration and amplitude of the inhibitory post-synaptic potential. The methods used in the present study provide a useful means of quantifying the effects of motoneuron excitability in detail.

Adult↗
PubMed1991

[Reflex response of the masseter muscle after percussion of the chin and electrical stimulation of the upper lip in patients with central motor disorders].

In 23 patients with central motor disorders (spastic hemiparesis, pseudobulbar syndrome and parkinsonism) reflex responses in both masseters were evoked during their relaxation and contraction by percussion with a reflex hammer on the chin and by electric stimulation of the upper lip. For recording of the reflex responses the electromyographic method was used. On the side of the spastic hemiparesis, as compared with the finding on the non-paretic side, the author found changes in the short-, medium and late-latency excitation and inhibition segments of the reflex response. In patients with parkinsonism the medium-latency portion of the reflex response after percussion of the chin from above as well as from below was satisfactory. The late latency excitation response after percussion of the chin from below was greater than its corresponding part evoked by percussion of the chin from above. In patients with the pseudobulbar syndrome the inhibitory parts of the reflex responses after percussion of the chin were weak. The results of the examination provided thus more detailed information on disorders of supranuclear control of masseter muscles.

Cerebrovascular Disorders↗
PubMed2003

Vertical jaw separation and masseter muscle electromyographic activity: a comparative study between asymptomatic controls & patients with temporomandibular pain & dysfunction.

The aims of the present study were to assess the relationship pattern between bilateral masseter muscle electromyographic (MEMG) activity recordings and vertical jaw separation (VJS). Asymptomatic subjects (n = 15) were compared with age and gender-matched patients (n = 18) with temporomandibular pain and dysfunction (TMPD); before and after undergoing interocclusal appliance (IOA) therapy for 4 months. In asymptomatic subjects a bilateral minimum MEMG activity was found in a 'resting zone' at approximately a quarter of maximum mandibular opening (mean, 15.4 mm of VJS; range, 5.5-22.5 mm including overbite). No overall relationship between MEMG and VJS was shown for patients with TMPD. After successful IOA therapy, the majority of TMPD patients (14 of 18) showed normalization of the relationship between MEMG and VJS, but electromyographic assessment was not found to be of value as a single objective assessment parameter in evaluating the resolution of TMPD or the effectiveness of IOA therapy.

Adolescent↗
PubMed2005

Role of capsaicin-sensitive primary afferent inputs from the masseter muscle in the C1 spinal neurons responding to tooth-pulp stimulation in rats.

The aim of the present study was to demonstrate the convergence of inputs from masseter muscle (MM) and tooth pulp (TP) onto C1 spinal neurons and to determine whether the afferent fibers express the functional vanilloid receptor (VR1). Extracellular single-unit recordings were made from 61 C1 units responding to TP electrical stimulation with a constant temporal relationship to a digastric electromyogram signal in pentobarbital anesthetized rats. Eighty-four percent of C1 neurons responding to TP stimulation also responded to the ipsilateral MM stimulation. Of these neurons, 61% were considered to be afferent inputs from Adelta-fibers and the remaining units (39%) were C-fibers, based on calculation of the nerve conduction velocity. Intramuscular injection of capsaicin (0.05 and 0.1%) produced a reduction in a MM-induced C1 neuronal activity in a dose-dependent manner and this effect was antagonized by pretreatment with an antagonist of VR1, capsazepine. Some of these units were also excited by noxious heat stimulation (> 43 degrees C). The trigeminal root ganglion (TRG) neurons that innervated the MM were retrogradely labeled with Fluorogold (FG) and the small-diameter FG-labeled TRG neurons expressed the immunoreactivity for VR1. After intramuscular mustard oil injection (noxious chemical stimulation), the C1 neuronal activity induced by both touch and pinch stimuli was enhanced and their receptive field sizes were significantly expanded. These changes were reversed within 15-20 min. These results suggest that there may be the convergence of noxious afferents inputs from the MM and TP afferents on the same C1 neurons in rats, and that the afferent fibers expressing the functional VR1 may contribute to the hyperalgesia and/or referred pain associated with temporomandibular joint disorder.

Action Potentials↗
PubMedDate not supplied

MR imaging of a lymphangioma involving the masseter muscle.

Lymphangiomas and cystic hygromas are tumors of lymphatic origin that are relatively common in the head and neck area. However, based on our literature review of this subject, the masseter muscle has never been implicated as a primary tumor site. It is our purpose to report such a case and to emphasize the value of magnetic resonance imaging for diagnosing a mass located in the masseteric region.

Adult↗
PubMed1989

[Characterization of calcium permeability at steady-state calcium load in masseter muscle sarcoplasmic reticulum].

To characterize the route of calcium permeability, the effect of intravesicular and extravesicular calcium concentration on the permeability from sarcoplasmic reticulum (SR) vesicles isolated from canine masseter muscle was determined by measuring net efflux of calcium after stopping pump-mediated fluxes. The apparent permeability, calculated as the net efflux divided by the total intravesicular calcium, depended on calcium load. When the intravesicular bound calcium was taken into account, net calcium efflux was found to be linearly related to the difference in calcium concentration across the SR membrane. The first order rate constant of calcium permeability was nearly identical when efflux was initiated by the addition of EGTA or glucose plus hexokinase to quench calcium pump by lowering activator calcium or by converting substrate ATP to ADP and glucose 6-phosphate, respectively. Extravesicular calcium concentration between 0.001 microM and 33.9 microM had no great effect on calcium permeability. The results suggest that some minimal calcium gradient may be required in order to observe a substantial passive calcium efflux, and the passive calcium efflux is not carrier mediated. It is also postulated that passive route of efflux during calcium accumulation is relatively small and that physiological calcium release during excitation-contraction coupling does not occur through this route.

Animals↗
PubMed1995

Masseter muscle activity and the hypoglossal nerve.

The effects of severing the hypoglossal nerve and resultant restriction of tongue movement was evaluated for its effect on masticatory jaw movement. Electromyograms of masseter muscles in the feeding rat were recorded 3 days after the nerve severing operation at 1 week intervals. Even after severing the lateral branches of the hypoglossal nerve bilaterally, active-feeding behaviour continued with mastication slightly impaired. After severing the medical branches bilaterally, feeding behaviour was rarely observed, but where eating did take place mastication was impaired with marked disturbance in the masticatory rhythm.

Animals↗
PubMed1999

Masseter muscle volume measured using ultrasonography and its relationship with facial morphology.

The aims of this study were to measure the volume, cross-sectional area, thickness, width, and length of contracted masseter muscles in a sample of adults, four males and six females, using three-dimensional (3D) ultrasonography, and to correlate these measurements with the variations in facial morphology of the sample. The scans were carried out bilaterally using a hand-held probe carrying a magnetic positional sensor, which enabled a computer to reconstruct the images into a 3D array of slices. Measurements were made by the computer from the reconstructed images using specially written software. Cephalometric analysis initially involved seven angular, eight linear, and two proportional variables, but as these were strongly inter-dependent, the variables were reduced to four principal components prior to statistical comparison with the mean muscle variables. The values found for muscle volume, cross-sectional area, and thickness were broadly consistent with those of previous investigators. Volume showed a significant, negative correlation with mandibular inclination including gonial angle (P < or = 0.001), and a significant, positive correlation with total posterior face height and ramus height (P < or = 0.001), and lower posterior face height percentage (P < or = 0.01). Weaker correlations were found for length and thickness. While the results support existing evidence that large masticatory muscles are associated with brachycephalism and vice versa, a cautious interpretation is necessary in view of the small sample size. The 3D ultrasonography system is at an experimental stage and requires further development and evaluation.

Adolescent↗
PubMed1981

The role in masseter muscle activities of functionally elicited periodontal afferents from abutment teeth under overdentures.

Five overdenture wearers with a small number of remaining natural teeth were selected to evaluate the effect of the afferent input from periodontal mechanoreceptors on masseter activity in man. As a control, a full denture wearer was included. The subjects were instructed to chew a piece of gum, and/or tap their teeth. Surface EmG from the bilateral masseter muscles were recorded and analysed. When functional pressure was applied, during chewing, to the abutment teeth as well as to mucosa through the denture base, masseter activities were encouraged. Following application of anaesthesia to the periodontal membrane of the abutments, masseter activities were reduced. The duration of the silent period (SP) appearing in the EMG burst following tooth tapping was significantly increased with root support compared to mucosal support only. With topical anaesthesia of the periodontal tissues, SP duration decreased significantly. In conclusion, it has become apparent that the pressure sensibility of abutment teeth bearing functional pressure under an overdenture base is capable of facilitating masseter activity, as one of the sources of oral sensory input during mastication.

Adult↗
PubMed2001

Post-translational phosphorylation of the slow/beta myosin heavy chain isoform in adult rabbit masseter muscle.

Four different phenotypes of slow muscle fibers, characterized by differential epitope expression in the slow/beta myosin heavy chain (MyHC) isoform, have been identified in adult rabbit masseter muscle. We investigated the role of post-translational phosphorylation in the expression of these four phenotypes. Serial cryostat sections were treated either with alkaline phosphatase to dephosphorylate proteins in the tissue, or with a brain kinase solution and ATP to phosphorylate them, and then stained, using four antibodies that bind specifically to the slow/beta MyHC isoform. In sections pre-treated with phosphatase, immunoreactivity to antibody A4.840 was abolished, but it could be restored by subsequent kinase/ATP treatment or ATP alone, indicating that the expression of its epitope requires phosphorylation. Phosphatase treatment resulted in an exposure of the epitope for antibody A4.951 in cells that normally bind this antibody only weakly or not at all, but since heat treatment alone produced similar effects, the role of phosphorylation in this enhancement is less certain. Immunoreactivity to antibodies S58 and BA-D5 were not influenced by phosphatase pre-treatment. Kinase/ATP treatment was only effective in changing antibody binding when tissues already had been phosphatase treated. We interpret these results to mean that sites of potential phosphorylation may already be occupied by O-linked glycosylation.

Animals↗
PubMed1995

[The relationships between the EMG excitation pattern of the masseter muscle and the facial skeletal morphology].

The purpose of this study was to investigate the correlations between malocclusions and the electromyographic activity of the orofacial muscles as this activity reveals itself through multi-channel, simultaneous recording of surface potentials from the masseter muscle. Thirty adults with class II or class III malocclusion formed the study's patient base. Surgical correction of the anomaly was planned for all patients. Ten patients served as the control group. In addition to the standard diagnosis, EMG were recorded during various stress situations such as maximal intercuspidations, chewing, swallowing, and mandible protrusion. We obtained a so-called "myomap" by means of the simultaneous multi-channel recording of the surface potential of the right masseter. Comparison of the EMG revealed a higher activity from the masticatory muscles in the class II cases than in the class III cases. The analysis of the masseter excitation pattern brought to light interesting differences. A higher activity on the lower margin of mandible in the area of the superficial part of masseter was found in the class II cases, whereas contrary to this an increase in EMG activity was found above the deep part of masseter in class III cases. The differing distribution of excitation of the 2 parts of the muscle in class II and class III malocclusions confirms the correlation between muscle function and morphology.

Adolescent↗
PubMedDate not supplied

[Split line patterns in the mandible after transposition of the insertion of the masseter muscle in the adult rabbit].

With the aim of studying in the fibrous structure of the compact bone, as revealed by the split-line technique, unilateral surgical transposition of the masseter muscle from the masseteric fossa to the central area of the mandibular body below the molar teeth was performed in seven adult rabbits. Six months later the animals were killed, their mandibles were removed, cleaned and then decalcified. Split-lines were made on the lateral surface of both the control and the operated side of the mandible. Myotransposition induced alterations in the split-line patterns; they showed to be entangled and disorganized, which mean structural changes in the bone itself.

Animals↗
PubMed1987

Proliferative myositis of the masseter muscle.

The authors present a case of a 33-year-old white man with a 4-month history of a rapidly enlarging, tender, painful, circumscribed facial mass located in the masseter muscle. CT scan and fine needle aspiration cytology, coupled with clinical assessment, suggested the diagnosis of proliferative myositis. Curative intraoral excisional biopsy was done, thereby avoiding a parotidectomy incision and approach to the lesion. The pathology showed proliferative myositis. A review of the literature revealed 36 cases which indicated that proliferative myositis is a relatively rare etiology of a head and neck mass. Careful clinical, radiologic, and pathologic evaluations were required to make this unusual diagnosis and avoid any unnecessary facial mutilation in its treatment.

Adult↗
PubMed1989

Proportionality of mean voltage of masseter muscle to maximum bite force applied for diagnosing temporomandibular joint disturbance syndrome.

Maximum bite force in the region of the right first maxillary molar and the corresponding mean voltage of the right masseter muscle of 29 patients suffering from temporomandibular joint dysfunction and 27 healthy controls were measured. In contrast with the controls, the maximum bite force of the patients was smaller (p less than 0.01), the mean voltage was nearly equal (p greater than 0.05), and the proportionality of the mean voltage to the maximum bite force of the patients was greater (p less than 0.01). These results tend to indicate that the masticatory muscles of patients with temporomandibular joint dysfunction are in a state of hyperactivity and tension. The proportionality method suggested in this article is more convenient and easier to apply than previously proposed methods that measure the slope of voltage/tension curves. It may, therefore, have clinical value in the diagnosis of patients with temporomandibular joint disorders.

Adolescent↗
PubMed1975

Vibration-induced discharge patterns of single motor units in the masseter muscle in man.

Single motor unit potentials were recorded with small bipolar wires from intact masseter muscles in the adult man and a detailed parametric analysis of the effects of muscle vibration on motor unit discharges was carried out. 2. When the vibration amplitude was kept constant, each unit started firing at a definite threshold of vibration frequency. With higher frequencies the rate of firing rapidly reached a maximum. Units recruited at higher frequencies presented a lower maximum rate of firing. 3. When the vibration frequency was kept constant, each masseter unit discharged at a definite threshold of vibration amplitude. With higher amplitudes the unit quickly reached a maximum rate of discharge. Units with a higher frequency threshold tended to also present a higher amplitude threshold. Motor unit "excitability" curves could be plotted using the combined threshold conditions for frequency and amplitude of applied vibrations. 4. With a given parametric set of vibration, the units only started firing at a given delay after the onset of vibration. The delay was quite different for different units and it increased considerably, sometimes by several seconds, when the vibration amplitude was made smaller. 5. In all the experimental conditions tested, and even when the unit discharge did not start until several seconds after vibration onset, the unit potential presented a close and highly consistent temporal relation to the vibration cycles. The slow recruitment process is thought to involve a polysynaptic excitatory mechanism which progressively depolarizes the masseter motoneurones close to their threshold, the actual firing being triggered by monosynaptic excitatory post-synaptic potentials from I(a) afferents, hence the small latency jitter recorded. This special pattern of tonic vibration reflex in jaw-closing muscles in man may result from the lack of reciprocal inhibition from the jaw-opening muscles.

Action Potentials↗