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PubMed1984

EMG activity of orbicularis oris superior, orbicularis oris inferior, and masseter muscles of articulatory disordered children.

The peak amplitude of EMG activity was measured from the orbicularis oris superior ( OOS ), orbicularis oris inferior ( OOI ) and masseter muscles for 8 normal and 8 articulatory disordered children, and 8 normal adults repeating/p ae/ at a fast rate. The three groups of subjects evidenced similar levels of average peak EMG activity across the three muscles; however, the articulatory disordered children exhibited less than normal variance for the OOI while the variability of performance of OOS and masseter muscles were similar to the normal speakers'. These data were interpreted as reflecting a limited degree of flexibility in the control of certain articulators that may affect the disordered children's ability to compensate during speech.

Adult↗
PubMed2007

Intramuscular cavernous hemangioma arising from masseter muscle: a diagnostic dilemma (2006: 12b).

We report here a case of intramuscular cavernous hemangioma of the right masseter muscle in a 41-year-old woman-misdiagnosed preoperatively as parotid tumor-along with its imaging and pathologic findings. Preoperative diagnosis of intramuscular cavernous hemangiomas of the masseter muscle is problematic, in that they may be confused with parotid tumor or other muscular lesions. In a patient with soft-tissue mass suspected of representing a hemangioma, MR imaging may provide more specific information regarding the characteristics, the origin, and the extent of the lesion than other imaging modalities.

Adult↗
PubMed1995

Variation of skin surface temperature over the masseter muscles in patients with myofascial pain following occlusal splint treatment.

The skin surface temperature (SST) over the masseter muscles was measured in 19 patients suffering from myofascial pain (MP) and 20 controls who had no history of any craniomandibular disorder. Seven measurements with intervals of 2 weeks were carried out. MP patients received an occlusal stabilization appliance during their second visit as their only treatment. Clinical symptoms, including muscle sensitivity to palpation, jaw movement and general feeling were evaluated at each visit and compared to baseline. The results indicated that SST in the control group remained almost unchanged throughout the study. In the MP group, the mean temperature decreased during the study after initial treatment. Accordingly, there was a probability of 88.5% that the occlusal appliance treatment in the MP group would cause a decrease of SST over the masseter muscle. A significant relationship between clinical improvement and a decrease of SST was found in the MP group. Temperature recordings with certain limitations could be an objective assessory tool in diagnosis and follow-up of patients with myofascial pain.

Adolescent↗
PubMed2001

Motor evoked potentials from masseter muscle induced by transcranial magnetic stimulation of the pyramidal tract: the importance of coil orientation.

BACKGROUND: Reliable recording of motor evoked potentials (MEPs) of the masseter muscle by transcranial magnetic stimulation (TMS) has proved more difficult than from facial or intrinsic hand muscles. Up to now it was unclear whether this difficulty was due to methodological and/or anatomical reasons. METHODS: The mechanism of pyramidal cell activation in masseter MEPs was investigated by using magnetic and electric transcranial stimulation. Analysing the effect of magnetic coil positioning and orientation over the scalp, and scrutinizing the masseter recording technique to avoid compound motor action potential (CMAP) contamination from facial muscles, an optimized method of masseter MEPs was developed. RESULTS: In particular, an antero-lateral inducing current orientation in the stimulating coil, approximately paralleling the central sulcus, proved clearly more effective for the masseter muscles than the postero-lateral orientation (P=0.005) found optimal for intrinsic hand muscles. The thus evoked masseter MEPs by transcranial magnetic stimulation (TMS) were found to be identical in shape, amplitude and latency as those evoked by transcranial electric stimulation (TES), evidencing a direct rather than trans-synaptic activation of the pyramidal cells. CONCLUSIONS: We conclude that in TMS evoked MEPs of masseter muscles, the direct stimulation of the pyramidal tract is more easily achieved than the trans-synaptic activation, which is in contrast to the intrinsic hand muscles. We hypothesize that the presynaptic projections to pyramidal cells of the masticatory muscles are less abundant than in hand muscles, and are therefore less accessible to trans-synaptic stimulation.

Action Potentials↗
PubMed1986

EMG activity of the orbicularis oris superior, orbicularis oris inferior, and masseter muscles of a cleft-palate child.

The peak amplitude of EMG activity was measured from the orbicularis oris superior (OOS), orbicularis oris inferior (OOI), and masseter muscles of a cleft-palate child and compared to data obtained from a normal child. Both children evidenced similar levels of average peak EMG activity and variability of performance across the three muscles. These data were interpreted to suggest that limitations in the function of the OOS, OOI, and masseter muscles do not contribute to the articulatory anomalies exhibited by the cleft-palate child.

Articulation Disorders↗
PubMed2001

Blood flow in and around the masseter muscle: normal and pathologic features demonstrated by color Doppler sonography.

OBJECTIVE: The purpose of this study was to clarify the normal findings of arteries in and around the masseter muscle and to present their pathologic changes with the use of color Doppler sonography. STUDY DESIGN: The vascular appearances were examined for the 4 main arteries feeding the masseter muscle in healthy volunteers (n = 38) and patients with inflammation (n = 5) and intramuscular hemangioma (n = 3). The features of these arteries were investigated together with the flow diameter, flow velocities, and arterial resistances. The symmetry indices were also calculated to assess the pathologic changes. RESULTS: The detection rates of the branch from the transverse facial artery, the masseter artery, and the branch from the maxillary or external carotid artery were 98.7%, 21.1%, and 84.2% in healthy volunteers, respectively. The facial artery that feeds the muscle from the inferior part represented 2 patterns according to anatomic variant: the masseteric branch (22.4%) and the main trunk itself (77.6%). The means of the flow diameter, maximum and minimum velocities, resistive index, and pulsatility index in healthy subjects were 1.8 mm, 24.6 cm/s, 5.1 cm/s, 0.80, and 2.51, respectively. In most of the patients with symptoms, the symmetry indices of all measurement values increased in comparison with those of healthy volunteers. CONCLUSION: Color Doppler sonography is useful in describing the arteries in and around the masseter muscle and has the potential of being used to depict the pathologic changes.

Adult↗
PubMed2001

Electromyographic analysis of fatigue in temporalis and masseter muscles during continuous chewing.

The aim of this study was to evaluate the electromyographic changes in the anterior temporalis and masseter muscles after fatigue induced by continuous chewing. Surface electrodes were placed bilaterally over the anterior temporalis and masseter muscles of 31 subjects with normal dentition. Recordings were taken every minute from the beginning of chewing to the exact moment the volunteer reported subjective sensation of fatigue in the jaw muscles. The length of endurance period (fatigue threshold) was measured to each subject, as well as the average amplitude and duration of activation phase and duration of relaxation phase through electromyographic recording of each muscle. The average endurance period was about 500 s. No significant change occurred on the average amplitude of activation phase meanwhile the duration of both the activation and relaxation phase diminished after fatigue.

Adolescent↗
PubMed1986

Hemangioma of the masseter muscle: a case report and review of the literature.

The case of a patient with a hemangioma of the masseter muscle is presented. The treatment in this case was superficial parotidectomy and resection of the hemangioma. A review of the literature reveals that the masseter muscle is a fairly uncommon location for hemangiomas. Among the cases reported the diagnosis was rarely made preoperatively. Most authors recommended that superficial parotidectomy be done as part of the surgical excision.

Adult↗
PubMed1989

[Muscle fiber conduction velocity and frequency parameters of surface EMG during fatigue of the human masseter muscle. 2. Frequency parameters].

During sustained isometric contraction of the jaw muscles, muscular fatigue causes a shift towards lower frequencies in the EMG frequency power spectrum. This shift is due to a reduction of myoelectric conduction velocity. The purpose of this study was to investigate the effect of surface electrode location on the estimates of frequency components, and to determine the appropriate frequency parameters of surface EMG which provided the best fit when comparing conduction velocity. Studies were performed in the masseter muscles of 8 healthy subjects. The myoelectric potentials were derived using 12 differential amplifiers from electrode arrays. The frequency parameters calculated were as follows: peak frequency, mean power frequency, cumulative power function (10, 25, 50 and 75%), median frequency ratio, low frequency ratio and measure H. As the results, following findings were obtained: 1. The high frequency content occurred at the region of end-plate zone and tendonous insertion of the muscle. 2. EMG spectra obtained during fatigue were shifted to lower frequencies for all regions except adjacent end-plate zone. 3. The relationships between conduction velocity and frequency parameters during fatiguing contractions were almost linear except peak frequency. 4. It was concluded that the location between distal end-plate and the tendon was "stable" zone for studying muscular fatigue.

Electromyography↗
PubMed1980

Effects of an occlusal splint on integrated electromyography of masseter muscle in experimental tooth clenching in man.

Six male subjects exercised maximal voluntary tooth clenching until fatigue appeared in the masseter muscle and until pains and exhaustion of this muscle could no longer be endured; that is, the fatigue threshold and the pain tolerance of the muscle were determined in seconds. An occlusal splint was inserted and the clenching exercises were repeated. During these exercises, and also during 10s of clenching, the electrical activity in the masseter muscle was recorded by bipolar surface electrodes and linearly integrated. Use of the splint did not result in significant changes in the subjective sensations of onset of fatigue and endurance of pain. As the periods of clenching increased, after insertion of the splint, the electrical activity decreased consistently, and use of the splint caused a significant decrease in the electrical activity of the pain tolerance test. As induced by the splint, there was no orderly pattern in changes of the fatigue thresholds and pain tolerances in relation to changes in the electrical activities of these parameters. The mode of action of the splint, in reducing the muscle activity, might have been that of stretching the elevator jaw muscles beyond their resting length.

Adult↗
PubMed2005

Myosin heavy chain protein and gene expression in the masseter muscle of adult patients with distal or mesial malocclusion.

The aim of this study was to determine the amount of myosin heavy chain (MyHC) proteins and MyHC mRNA in muscles of patients with different positions of the mandible. Ten adult patients for orthognathic surgery were divided into two groups: distal and mesial malocclusion. The mRNA expression of two MyHC isoforms of the anterior and posterior part of the right and left side of the human masseter muscle was analysed with a competitive RT-PCR assay. An exogenous template that includes oligonucleotide sequences specific for sarcomeric MyHC isoforms (1 and 2x) was constructed and utilized as competitor. Different isoforms of the MyHC protein were identified by Western blot analysis. In the total mRNA pool of the masseter muscle, the MyHC 1 mRNA level was 25.5 +/- 7.6% and the MyHC 2x mRNA was 2.5 +/- 1.2%. The anterior part of the masseter muscle from patients with distal occlusion contained more type 1 and 2x MyHC mRNA, as compared to patients with mesial occlusion (P < 0.05). No difference in the protein distribution was observed. The differences in mRNA expression may be caused by the enforced stress of the masticatory muscle in distal occlusion because of the disadvantageous pivot.

Adult↗
PubMed1989

Masseter muscle adaptation following surgical correction of vertical maxillary excess.

This study was designed to examine the adaptive response of the human masseter muscle following surgical correction of abnormal facial form. Biopsies of the deep surface of the anterior superficial masseter muscle were obtained from five patients demonstrating vertical maxillary excess (VME), one at the time of corrective surgery, and a second at a long-term postoperative time interval (mean, 8 months). Control biopsies were also obtained from five individuals (three cadavers and two patients) with normal dentofacial morphology. A standard regimen of histologic and histochemical staining was used to classify individual muscle fibers as either type 1, type 2, or intermediate. In both VME patients and normal subjects type 1 fibers predominated, with the control group displaying a higher percentage (50% vs. 43%). On the average, type 1 fibers also had the largest areas. Following surgery there was an increase in type 2 fibers (30% vs. 52%). Two patients receiving maxillary surgery only exhibited either no change in mean fiber area or only a slight increase. The three remaining patients who underwent concomitant maxillary and mandibular surgery all showed a significant decrease in mean fiber area. Two persons in the latter group also showed features consistent with a denervation-reinnervation process. The results of this study indicate that the human masseter responds to surgical manipulation of the jaws in a histochemically demonstrable manner, with the nature and magnitude of the response associated with the particular surgical procedure(s) performed.

Adaptation, Physiological↗
PubMed2005

Fiber-type differences in masseter muscle associated with different facial morphologies.

BACKGROUND: The influence of muscle forces and associated physiologic behaviors on dental and skeletal development is well recognized but difficult to quantify because of the limited understanding of the interrelationships between physiologic and other mechanisms during growth. METHODS: The purpose of this study was to characterize fiber-type composition of masseter muscle in 44 subjects during surgical correction of malocclusion. Four fiber types were identified after immunostaining of biopsy sections with myosin heavy chain-specific antibodies, and the average fiber diameter and percentage of muscle occupancy of the fiber types were determined in each of 6 subject groups (Class II or Class III and open bite, normal bite, or deepbite). A 2 x 3 x 4 analysis of variance was used to determine significant differences between mean areas for fiber types, vertical relationships, and sagittal relationships. RESULTS: There were significant differences in percentage of occupancy of fiber types in masseter muscle in bite groups with different vertical dimensions. Type I fiber occupancy increased in open bites, and conversely, type II fiber occupancy increased in deepbites. The association between sagittal jaw relationships and mean fiber area was less strong, but, in the Class III group, the average fiber area was significantly different between the open bite, normal bite, and deepbite subjects. In the Class III subjects, type I and I/II hybrid fiber areas were greatly increased in subjects with deepbite. CONCLUSIONS: Given the variation between subjects in fiber areas and fiber numbers, larger subject populations will be needed to demonstrate more significant associations between sagittal relationships and muscle composition. However, the robust influence of jaw-closing muscles on vertical dimension allowed us to conclude that vertical bite characteristics vary according to the fiber type composition of masseter muscle.

Adult↗
PubMed1998

A metabolism study of human masseter muscle by 31P magnetic resonance spectroscopy during long periods of exercise and recovery.

The metabolism of the human masseter muscle was investigated using phosphorus (31p) magnetic resonance spectroscopy (MRS) during long periods of exercise and recovery. Eleven subjects aged 19 to 28 yr were examined by 31p MRS during four consecutive periods of 13 min each: rest, exercise, recovery 1 and 2. For each subject, a biting force equal to 20% of maximum voluntary biting force was applied and controlled during the exercise period to produce maximum fatigue. 31p MR spectra were localized from a 24 cm3 volume of interest using an image selected in vivo spectroscopy (ISIS) sequence and a 6 cm diameter surface coil placed on the left masseter. Compared to the resting level, the phosphocreatine (PCr) content decreased by 26% during exercise, while the inorganic phosphate (Pi) concentration increased by 65%. During the two recovery periods, the Pi content remained decreased compared with the resting level by 36% and 30%, respectively. The Pi/PCr ratio was increased from 0.30+/-0.04 at rest to 0.63+/-0.13 during exercise while the adenosine triphosphate (ATP)/Pi ratio was decreased. The pH decreased from 7.02+/-0.03 to 6.93+/-0.04 during exercise and returned to control level (7.09+/-0.08) only during the second recovery period. These results suggest that the masseter muscle is characterized by high ATP turnover and, therefore, high oxidative phosphorylative activity in agreement with its constitution of predominantly fatigue resistant type I fibers.

Adenosine Triphosphate↗
PubMed1983

Cephalometric analysis of adaptations after lengthening of the masseter muscle in adult rhesus monkeys, Macaca mulatta.

This relationship between the function of the muscles of mastication and craniofacial form was investigated in young adult monkeys by increasing the functional length of the elevator muscles of the mandible non-invasively by a bite-opening splint cemented to the maxillary dentition. The major adaptations to increased vertical dimensional were (1) marked superior and some anterior displacement of the maxillary complex, (2) dental intrusion and (3) rotation of the mandible. These alterations produced a shortening of the lengthened masseter muscle, i.e. a reduction in the amount of muscle stretch brought about by the appliance. Migration of the masseteric insertion along the ramus did not contribute significantly to the pattern of adaptation. The role of the masseter muscle in craniofacial adaptations to altered vertical dimension was determined by detaching and re-attaching the insertion of the masseter muscle in one group of experimental animals. The myotomized monkeys experienced significantly less anterior displacement of the maxilla than the non-myotomized monkeys, indicating that the surgery may have lessened some of the anteriorly-directed distracting forces of the lengthened masseter. Masseter myotomy alone was not sufficient to eliminate the vertically-directed distracting forces of the remainder of the mandibular elevator muscles brought about by increasing the vertical dimension of the lower face.

Adaptation, Physiological↗
PubMed1995

[Immunochemical and immunohistochemical study of calpastatin, an endogenous calpain inhibitor, in the masseter muscle of the rabbit].

The calpains-calpastatin system (calcium-activated neutral proteases and endogenous inhibitor) seems to be, in the skeletal muscle, a fine enzymatic system of myofibrillar turnover regulation, in normal as well as pathological conditions (for ex., dystrophic muscle). The purpose of the research is to establish in qualitative and quantitative terms whether the level of calpastatin can evidence differences between a muscle in normal activity conditions and one having dysfunctional alterations experimentally induced. So the masseter muscle of rabbit in normal conditions and with experimentally modified occlusal plane has been used. Our results confirm the presence of the 68 KDa calpastatin in the masseter muscle. The presence of the inhibitor in the same subcellular structures in which the calpains have been detected (myofibrillars, sarcolemma, endomysial connective) has been confirmed. Finally, variations in calpastatin amount in the muscle of animals experimentally treated with respect to the controls have been found. Thus, calpastatin seems to act as a marker of muscle dysfunctions connected to occlusal plane alteration and to loss of vertical dimention.

Animals↗
PubMed1989

[Effect of compound 48/80 on masseter muscle sarcoplasmic reticulum calcium transport system].

To define the role of calmodulin in Ca2+ fluxes behavior of canine masseter muscle sarcoplasmic reticulum (SR) vesicles, the effect of condensation product of N-methyl-p-methoxy-phenethylamine with formaldehyde (compound 48/80), a selective and powerful inhibitor of calmodulin-regulated function, on Ca(2+)-ATPase activity, oxalate-supported Ca2+ uptake velocity, and on interaction with Ca2+ permeability and Ca2+ loading at steady-state were evaluated. Compound 48/80, at concentrations of 10 to 100 micrograms/ml, reduced oxalate-supported Ca2+ uptake velocity without affecting Ca(2+)-ATPase activity. In the presence of 10 micrograms/ml compound 48/80, there was a shift of pH- or temperature-response curve of oxalate-supported Ca2+ uptake velocity, but not of Ca(2+)-ATPase activity, down. It was found that Arrhenius plots of the Ca(2+)-ATPase activity show a break at about 21 degrees C in the presence or absence of 10 micrograms/ml compound 48/80, and that compound 48/80 has no effect on Arrhenius plots of the oxalate-supported Ca2+ uptake velocity. Furthermore, Ca2+ loading at steady-state, but not passive Ca2+ permeability, was decreased by compound 48/80 at low concentrations (1-2 micrograms/ml). The results of this study suggest that calmodulin-dependent process plays a functional role in the coupling of ATP hydrolysis and Ca2+ accumulation, perhaps through regulation of Ca2+ release channels in masseter muscle SR membrane. Calmodulin-dependent component of Ca2+ fluxes in the SR vesicles may be directly modified by compound 48/80, thereby diminishing Ca2+ accumulation without affecting the Ca2+ uptake mechanism.

Animals↗
PubMedDate not supplied

Peculiar characteristics of the insertion area of the masseter muscle in rats. Scanning electron microscopic study.

The structure of the bone surface of the insertion area of the masseter muscle was studied in 20 albinus Wistar rats. Specimens were fixed in a modified Karnovsky solution and treated according to the technique described by LESTER et alii and examined in a JEOL scanning electron microscope, JSM-P15. The results showed that the insertion area of the masseter muscle of rats presents a smooth surface covered by thick layers of calcified collagen fibers. In adjacent areas of the lower edge of the mandibular angle an irregular surface with bone reabsorption and foraminae was observed. The vascular foraminae measure from 30 to 50 microns in diameter and the distance between them ranges from 200 to 460 microns. Osteocyte lacunae were seen at the surface and their measures range from 18 to 25 microns in diameter, which were surrounded by collagen fiber bundles of longitudinal disposition.

Animals↗