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At least 433 records · Page 24Linked to original sources
PubMed2001

Constancy of masseter muscle structure and function with age in F344 rats.

Senile muscle atrophy is a characteristic feature of advancing age. Despite the growing body of knowledge about weight-bearing muscles in rodents and man, there is relatively little such information on the muscles of mastication. Therefore, the primary goal here was to develop a masseter muscle preparation from male Fischer 344 rats suitable for studying contractile characteristics in vitro. And, secondarily, the goal was to examine this preparation for evidence of age-related changes in muscle composition and function in rats aged 4--24 months. Histochemical analysis of the composition of the four anatomical regions (branches) of the masseter revealed a mixture of rapidly contracting, fatiguable and fatigue-resistant muscle fibres with no significant differences between branches. Fibre type and size were determined with myosin ATPase, NADH-TR and toluidine blue staining of quick- frozen muscle sections. No significant changes in fibre type or fibre area were found with increasing age. One branch of the masseter, the anterior deep masseter, is sufficiently thin (less than 0.8 mm thickness) for adequate diffusion of oxygen and nutrients in studies of isometric contractile properties in vitro. Contraction time, half-relaxation time, dry weight:wet weight ratio and maximum force per unit area were found to be similar in muscles of young and old rats. Our results demonstrate that the anterior deep masseter of the rat is a suitable preparation for investigating masseter function in vitro. The surprising absence of age-related changes in composition and function is consistent with some, but not all, data on ageing rodent limb muscles. The results suggest that masticatory muscle performance is preserved with age in rats.

Aging↗
PubMed1988

Electromyographic biofeedback and sustained masseter muscle contraction in man.

Twenty-two human subjects performed sustained voluntary contractions of the mandibular elevator muscles firstly without and secondly with visual biofeedback. The level of electromyographic activity of the masseter muscle during the second clench exceeded that during the first clench by a mean of 36%. This differential indicates the ability of the subjects to override the central factors which normally limit muscle activity during a fatiguing contraction.

Adult↗
PubMed1994

Stereotactic location of EMG needle electrode scans relative to tendons in the human masseter muscle.

A method is presented for locating the positions of moving electromyographic needle electrodes relative to internal tendinous boundaries within the human masseter muscle. It combines scanning electromyography, needle electrode tracking, magnetic resonance imaging, and three-dimensional stereotactic reconstruction. The technique is useful for investigating motor unit territory within the masseter and other complex craniofacial muscles.

Electrodes, Implanted↗
PubMed2005

Fatigue and damage to the masseter muscle by prolonged low-frequency stimulation in the rat.

This study aimed to examine peripheral fatigue and the resultant damage to the masseter muscle due to prolonged low-frequency stimulation. Thirty male rats were divided into S1, S2, S4, Dantr and Sham groups. The left masseters were used as experimental muscles. A pair of stimulation electrodes was placed on the left masseter. A stimulating session included rectangular electric pulses of 18 Hz (5 mA, approximately 18 V, 0.7 ms) for 2 h with a 3 min rest period between sessions. One session was given to the S1 group, two sessions to the S2 group and four sessions to the S4 group. Four sessions were given to the Dantr group with administration of dantrolene to determine any artifacts of the electrical current. No electric stimulation was given to both side masseters in the Sham group or to the control (right) masseters in the other groups. In each session, jaw-closing force increased to a peak within 1 min and attenuated to the steady force. The peak force decreased as the session advanced in each group. Both side masseters were dissected after the stimulations and examined histologically. The experimental masseter was significantly heavier than that of the controls in the S1, S2 and S4 groups, and the muscle fibres showed irregularity of size and shape with enlargement of interstitial space and infiltration of mononuclear cells into the fibres. However, no such histological change was observed in the Dantr and Sham groups. It was confirmed that fatigue and damage to muscle fibres could be induced in masticatory muscles by prolonged low-frequency stimulation.

Animals↗
PubMed1984

Short and long-latency responses in human masseter muscle evoked by chin taps.

Ten healthy subjects received downward, backward and upward chin taps with standardized force and direction. Taps in all three directions elicited short (M1) and long (M2 and M3)-latency excitatory EMG responses in the masseter muscle. M1 (mean latency 8.9 ms, amplitude 150 microV) occurred more frequently and with shorter latency during clenching than during relaxation or opening. Downward taps were more efficient in evoking jaw-jerks (25 per cent) than upward (14 per cent) and backward ones (16 per cent). M2 was a weak biphasic deflection occurring during the silent period (mean latency 42 ms, amplitude 87 microV) and M3 was an EMG burst following the silent period (mean latency 69.3 ms, amplitude 169 microV). No long-latency evoked responses were obtained from the relaxed masseter. Thus, muscle stretch increases M1 response frequency but is not a necessary prerequisite. The hypothesis that vibratory transmission plays an important role was confirmed. Voluntary activation of the stimulated muscle (clenching) increases M1-response frequency and shortens response latency.

Adult↗
PubMed2003

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

A rare case of cervicofacial actinomycosis arising primarily in the masseter muscle is described. The patient was a healthy 74-year-old woman who was not immunocompromised and had no other primary pathological finding in the oral cavity. The importance of the differential diagnosis for this unusual infection is demonstrated with tumoral pathological findings. Possible predisposing factors as well as diagnostic and therapeutic methods are discussed.

Actinomycosis, Cervicofacial↗
PubMed2002

Skin surface temperature over the temporomandibular joint and masseter muscle in healthy children and adolescents.

Skin surface temperature (SST) measurements were carried out over the temporomandibular joint (TMJ) and masseter muscle (MM) of 159 healthy children and adolescents aged 7, 11, 15 and 18 years. No current symptoms were found of impaired general health or from the masticatory system or recurrent headache. The recordings were done with a thermocouple in contact with the skin. The mean SST over the TMJ and MM increased with age, and from the youngest to the oldest group regarding the TMJ by 1.3 degrees C (right) and 1.6 degrees C (left), and for MM by 2.1 degrees C (right) and 2.5 degrees C (left). Variation in the mean difference between sides of the TMJ was 0.0-0.2 degrees C and for the MM 0.1-0.3 degrees C. The variation in SST between sides was reduced with increasing age, but was higher for MM than for TMJ in all age groups. In the 7-years group, there was a significant difference between right and left SST over TMJ and MM. It is concluded that SST increases with growth during childhood and that the SST for the TMJ is higher than MM in all age groups. The finding of a high degree of thermal symmetry between sides in all age groups may have diagnostic potential for pathological conditions involving blood flow and in evaluation of treatment of these conditions.

Adolescent↗
PubMed1994

A comparison of human masseter muscle thickness measured by ultrasonography and magnetic resonance imaging.

Non-invasive imaging techniques such as computerized tomography, magnetic resonance imaging (MRI), and ultrasonography enable measurements of the cross-section and thickness of human jaw muscles in vivo, providing an indication of the maximal force a muscle can exert. In 15 adult Caucasian men the thickness of the masseter muscle was registered bilaterally on three different levels by ultrasonography. Scans were made on the contracted and relaxed muscle. A comparison was then made with measurements from serial MRI scans, using univariate analysis of variance for repeated measurements and Pearson's correlation coefficients. Variances of the repeated measurements were calculated for the different scanning levels and the different muscle conditions and tested for homogeneity. For both the ultrasound and MRI measurements there was no difference in thickness between the left and right muscle. The registration level with highest reproducibility was halfway between the origin and insertion. Measurements from the contracted muscle were more reproducible than those from the relaxed muscle. The relaxed muscle thickness measured by ultrasonography was smaller than that measured by MRI. The correlation between ultrasound and MRI was significant for the upper and middle level of scanning (p < 0.001). The highest correlation was found between MRI (relaxed) and ultrasound (contracted) at the middle level (R = 0.83, p < 10(-6)). The conclusion is that ultrasonography is an accurate and reproducible method for measuring the thickness of the masseter in vivo. It allows for large-scale longitudinal study of changes in jaw-muscle thickness during growth in relation to change in biomechanical properties of masticatory muscles.

Adult↗
PubMed1977

A comparative histochemical study of the masseter muscle of the cattle, sheep, swine, dog, guinea pig, and rat.

The masseter muscles of different mammals were studied by means of hisotchemical reactions: NADH: Nitro BT oxidoreductase (NADHOX), 3-hydroxybutyrate: NAD+ oxidoreductase (HBOX), glycerol-3-phosphate: menadione oxidoreductase (GPOX), and acid-stable and alkali-stable myosin adenosine triphosphatase (ATPase). The masseter mucles of cattle and sheep consisted only of the fibres that reacted moderately for GPOX and strongly for NADHOX, HBOX, and the acid-stable ATPase. The masseter fibres of rats and guinea pigs reacted uniformly and strongly for GPOX and the alkali-stable ATPase. The fibres of the rats showed a weak to strong reaction for NADHOX and mostly a negative reaction for HBOX, whereas those of the guinea pigs reacted uniformly and strongly for NADHOX and HBOX.The masseter fibres of swine and dogs showed a weak or strong reaction for the alkali-stable and a negative or weak reation for HBOX. The fibres of the swine were weak to strong in NADHOX activity and those of the dogs uniformly strong; the fibres of the two species gave a moderate to strong reaction for GPOX. The masseter fibres of the ruminant differed from those of the other species in histochemical properties, and appeared to have the histochemical characteristics that meed functional demands for slow, long-term exercise.

Adenosine Triphosphatases↗
PubMed2001

Effect of chronic uncontrollable stress on myosin heavy chain expression in rat masseter muscle.

This study has evaluated the influence of chronic uncontrollable painless stress on the expression of myosin heavy chain (MyHC) isoforms in deep and superficial parts of the rat masseter muscle. Muscle cross sections of three month old Wistar rats were processed for immunohistochemical staining. In control muscle the three adult fast MyHC isoforms (-2a, -2x/d, -2b), were nonhomogenously distributed: in the smaller anterior part of the muscle only fast MyHC isoforms were expressed. The major superficial and posterior part of the muscle fibres also contained MyHC-1 (10%) and only 7% expressed of MyHC-2b. Psychological stress significantly modified the expression of particular MyHC isoforms in both parts of the muscle. In the anterior part of the experimental masseter the proportion of MyHC-2b expressing fibres decreased and 10% of the muscle fibres expressed MyHC-1. The superficial and posterior part of the experimental muscle contained significantly more muscle fibres expressing MyHC-2b isoforms. Regarding whole cross-sectional area transition towards faster phenotype was evident due to a higher percentage of either pure MyHC-2b containing fibres or hybrid MyHC-2x/d and -2b expressing fibres. The results of this study demonstrate that psychological stress is accompanied by a modification of muscle phenotype which is region specific. Opposite changes in deep and superficial part of the muscle could be ascribed to differences in genetic programme, function or susceptibility to hormones in both parts of masseter.

Animals↗
PubMed2004

The association between the masseter muscle, the mandibular alveolar bone mass and thickness in dentate women.

OBJECTIVE: Since muscle strength has been demonstrated to affect the bone in the long bones and spine, the possibility exists that the bone mass and dimension of the alveolar processes could be influenced by the function of the masticatory muscles. Therefore, the purpose of this study was to investigate whether two local factors (ultrasonographic masseter thickness, and occluding teeth) plus the skeletal bone mineral density (BMD) affect the mandibular alveolar bone mass (MABM) and the bucco-lingual alveolar thickness of the alveolar process. DESIGN: The thickness of the masseter muscle was evaluated by ultrasound imaging in 62 dentate women (40-75 years) with no periodontal disease and no dental infection in the premolar region consecutively selected from the patients in a public dental clinic. MABM was evaluated using periapical radiographs. The bucco-lingual thickness of the alveolar process was measured on dental casts with a dial calliper. BMD of the forearm was determined with dual energy X-ray absorptiometry. RESULTS: Multiple regression analyses demonstrated that masseter thickness and the number of occluding mandibular teeth in the lateral segment were significant determinants of MABM and of the interdental thickness, but BMD was not. The number of years after menopause and struma/gastro-intestinal disease influenced MABM but not the alveolar thickness. CONCLUSION: The local factors played an important role in the posterior mandibular segment and their effect might partly explain the low correlation between MABM and skeletal BMD.

Adult↗
PubMedDate not supplied

Exteroceptive silent period of masseter muscle activity evoked by electrical mental nerve stimulation: relation to non-pain and pain sensations.

Exteroceptive silent periods (ESPs) of masseter muscle activity evoked by electrical stimulation of the mental nerve were studied over a large range of prepain intensities and at pain threshold in 44 normal subjects. Seven levels of stimulus intensity, based on individual sensory and pain thresholds, were applied and the relationship between ESPs, stimulus intensity and perception, as manifested by the subjective verbal response, was investigated. The analysis revealed that the occurrence of ESPs was not related to the stimulus intensity at the pain threshold. There were individually different patterns of progressive response to increasing current intensities within the pre-pain range in many cases. On the other hand, almost half of all the subjects investigated showed no or only occasional ESPs. In view of this variability the concept of ESPs being a nociceptive behavioural response has to be questioned.

Adult↗
PubMed1990

Malignant hyperthermia susceptibility in adult patients with masseter muscle rigidity.

We sought to determine the incidence of malignant hyperthermia (MH) susceptibility in adult patients with a previous episode of masseter muscle rigidity (MMR). The medical records and in vitro contracture test results of all patients over 15 years of age tested for MH because of previous MMR from 1985 to 1988 were reviewed. The number of children (age less than 16 yr) tested for MH because of previous MMR was also determined for the same four-year period, for comparison of coincidence rates. Six of 24 adult patients (25 per cent) were proved MH-susceptible by in vitro contracture testing. No clinical sign associated with the episode of MMR was predictive of MH-susceptibility. Two of six MH-susceptible patients developed acute MH following MMR. In the same four-year period, 75 children were tested for MH-susceptibility because of previous MMR; 44 (59 per cent) had a positive in vitro contracture test. We conclude that the coincidence of MMR and MH-susceptibility is lower in adults than children. Episodes of acute MH do occur after MMR, but the onset of MH may be delayed. Conservative management of MMR in adult patients is recommended.

Adult↗
PubMed1986

Masseter muscle nodule due to bruxism. A case in point.

A 16-year-old white boy had a soft subcutaneous mass in the right masseter muscle. The pediatrician and two surgeons the patient had previously consulted had disagreed as to the origin of the mass and its treatment; their recommendations had ranged from leaving it alone to surgical excision. Treatment involved an orthopedic oral appliance restoring vertical dimension to its genetic norm and galvanic muscle stimulation. After 1 year the mass was eliminated.

Adolescent↗
PubMed1992

Discrimination of clenches at varied jaw positions using autoregressive model coefficients of myoelectrical activities of anterior temporal and masseter muscles.

During 10% maximum clenching at intercuspal, protruded, retruded contact and lateral positions, the surface electromyograms (EMG) of bilateral anterior temporal and masseter muscles of 20 normal subjects with intact natural dentitions were recorded. The autoregressive (AR) model of the sampled EMG was then built and the obtained coefficients of the AR model were accepted as featured parameters of the EMG. Finally Bayes' stepwise discriminant analysis was used for establishing discriminant functions of estimating low level clenches at varied jaw positions. It was found that total conformation rates of internal and external sample substitution (15 and 5 subjects) were 82.67% and 78% respectively; the discriminant effect between intercuspal and retruded contact position was not up to predicted standard. The results indicate that AR model coefficients may describe the characteristics of surface EMG of masticatory muscles and easily be used in multiple statistical analysis, from which the classification and diagnosis may be taken.

Adult↗
PubMed1994

Masseter muscle rigidity and malignant hyperthermia susceptibility in pediatric patients. An update on management and diagnosis.

BACKGROUND: Controversy exists regarding the definition of masseter muscle rigidity (MMR) and anesthetic management after MMR. This study reports current anesthetic management after MMR, estimates the incidence of clinical malignant hyperthermia (MH) in patients with MMR, and is the first to evaluate the coincidence of MMR with malignant hyperthermia susceptibility (MHS) according to the 1987 North American Malignant Hyperthermia Group protocol. METHODS: Practicing anesthesiologists referred pediatric patients for biopsy between 1986 and 1991 based on evidence of MMR after succinylcholine (1975-1991). The clinical scenario was described as MMR alone or MMR followed by signs of MH, including arterial CO2 tension > 50 mmHg, arterial pH < or = 7.25, and base deficit > 8. Patients had caffeine-halothane muscle contracture testing to determine MHS. RESULTS: Seventy patients (50 boys and 20 girls) were evaluated. Eighty-three percent (58 of 70) of anesthetics were halothane-succinylcholine. In 68% (48 of 70) of cases, the anesthetic was discontinued, whereas anesthesia was continued with nontriggering agents in 11% (8 of 70) and with triggering agents in 13% (9 of 70). Fifty-nine percent (41 of 70) of patients were diagnosed as MHS by muscle biopsy. In 7% (5 of 70) of patients, clinical MH developed within 10 min of MMR. CONCLUSIONS: This study, by using the current North American Malignant Hyperthermia Group protocol, reaffirms the high incidence (59%, 41 of 70) of MHS associated with MMR as confirmed by muscle biopsy. Of the MHS patients, 5 developed signs of clinical MH. Most anesthesiologists in this study, when confronted with MMR, discontinued anesthesia. Because of the potential lethality of MH and the > 50% concordance between MMR and MHS, the most conservative course of action after MMR is to discontinue the anesthetic and observe the patient for clinical evidence of MH. An acceptable alternative, depending on the urgency of the surgery, would be to continue anesthesia with nontriggering agents for MH, with appropriate monitoring.

Adolescent↗
PubMed1998

Responses of masseter muscles to transcranial magnetic stimulation in patients with amyotrophic lateral sclerosis.

We recorded motor responses evoked by transcranial magnetic stimulation (TMS) in the masseter muscles of 30 patients with amyotrophic lateral sclerosis (ALS), 10 patients with cervical spondylotic myelopathy (CSM) and 22 age-matched normal controls. Responses to direct activation of the trigeminal motor root (R-MEPs) were normal both in ALS and CSM patients. Responses to activation of cortico-bulbar descending fibers (C-MEPs) were absent or delayed in 19 ALS patients (63.3%). Abnormalities of masseter C-MEPs were more frequent than abnormalities of limb MEPs and could be observed both in patients with (77.8%) and without (41.7%) clinical bulbar signs. Masseter C-MEPs were normal in all CSM patients. Recording masseter responses to TMS can reveal the frequent impairment of cortico-bulbar projections in ALS and can be useful in the differential diagnosis of spinal cord compression disorders mimicking ALS because of combination of upper and lower motor neuron signs.

Aged↗