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PubMed1994

The incidence of masseter muscle rigidity after succinylcholine in infants and children.

To determine whether the incidence of masseter muscle rigidity is affected by the anaesthetic induction sequence, we prospectively studied for ten months the anaesthetic course in 5,641 infants and children who received muscle relaxation to facilitate tracheal intubation. The anaesthetic induction sequence consisted of intravenous sodium thiopentone (STP) 5 mg.kg-1 alone, halothane induction alone 1-4%, or halothane followed by STP. Inhalational inductions with halothane included nitrous oxide and oxygen. Tracheal intubation was facilitated by either intravenous succinylcholine (Sch) at least 1.5 mg.kg-1 or by a non-depolarizing muscle relaxant. The induction sequence and all episodes of MMR were recorded. Ninety percent of the patients received Sch and 10% received a non-depolarising agent. Of those who received Sch, 88% (5,064 patients) were anaesthetised with STP and 12% (607 patients) were anaesthetised with halothane alone or halothane followed by STP. Masseter muscle rigidity was defined clinically by the transient inability to distract the mandible from the maxilla such that the mouth could not be opened or could only be opened with force. No children anaesthetised with STP followed by Sch developed MMR. One child (0.9%) developed MMR after halothane and Sch and two developed MMR after halothane, STP and Sch (0.4%). The incidence of MMR after Sch was less with STP than with halothane alone or with halothane and STP (P < 0.025). The peak CPK values in the three children who developed MMR were 17,580 IU.L-1 after halothane and Sch, and 7,280 IU.-1 and 3,273 IU.-1 after halothane, STP and Sch. There was no evidence of MH reactions in these patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗
PubMed1998

Relationship between mandibular position and the coordination of masseter muscle activity during sleep in humans.

Although bruxism has been regarded as having a possibly important role in the aetiology of craniomandibular disorders, the activity of masticatory muscles relative to mandibular position during sleep grinding as recorded by electromyography (EMG) has not yet been clarified. Surface EMGs of the bilateral superficial masseter muscles were recorded simultaneously with mandibular position during sleep from 12 volunteers for three consecutive nights. The incidence of two mandibular positions were recorded with magnetic sensors for both left- and right-sided mandibular grinding. One of the mandibular positions was the canine edge-to-edge position, and the other was the midpoint between the intercuspal position and the canine edge-to-edge position. The mode of the working/ balancing activity ratio ranged from 1/10 to 2/10, showing the marked predominance of balancing side masseter muscle activity during sleep grinding. During sleep grinding, EMG bursts of masseter muscle were observed mainly with mediotrusive mandibular movement from the canine edge-to-edge position. From the results of the present study, it is suggested that muscular dynamics during sleep are unique compared to that during voluntary clenching, and exert a greater mechanical load to the balancing side temporomandibular joint.

Adult↗
PubMed2003

The effect of glutamate-evoked masseter muscle pain on the human jaw-stretch reflex differs in men and women.

AIMS: To compare jaw-stretch reflex responses in male and female subjects and to determine whether injection of glutamate into the masseter muscle facilitates these responses in both sexes. METHODS: Jaw-stretch reflex responses were evoked with a muscle stretcher, and pain intensity was scored by 11 men and 13 women before and after the injection of glutamate (1.0 mol/L, 0.2 ml) into the masseter muscle. The subjects rated glutamate-evoked pain intensity on a visual analog scale. RESULTS: Baseline jaw-stretch reflex responses were larger and glutamate injections into the masseter muscle were significantly more painful in women than in men, however, glutamate significantly facilitated jaw-stretch reflex responses in men but not in women. CONCLUSION: These results suggest that there is a significant sex-related difference in human jaw-stretch reflex responses and their modulation by painful stimuli. Since one possible function of facilitated jaw-stretch reflex responses during jaw muscle pain may be to reduce jaw mobility and thus protect against further exacerbation of an existing injury, the finding of a sex-related difference in modulation of jaw-stretch reflex responses may prove to be important in clarifying why the prevalence of temporomandibular disorders is greater in women than in men.

Adult↗
PubMedDate not supplied

[Initial masseter muscle fatigue in maximal voluntary teeth clenching].

Fatigue of striated muscles is defined as the impossibility to generate the expected or required force during the repeated contraction. During the maximal voluntary teeth contraction in the position of central occlusion the initial fatigue in masticatory muscles during the isometric contraction occurs. If a person can clench its teeth continuously and voluntarily it has a diagnostic significance since the peripheral fatigue is that important factor in the masticatory muscles activity, which is in direct correlation with the function of the masticatory system. The aim was to compare the obtained results of the initial fatigue of masseter muscles during the maximal voluntary teeth contraction in subjects with naturally healthy intact dentition and subjects with a pair of new full dentures. The investigation comprised 20 subjects with healthy stomatognathic system of the skeletal class I by Angle. Comparison of the values of the obtained results was performed electromyographically by synchronous registration of action potentials of masseter muscles. Results of the investigation of the onset of initial fatigue of masseter muscles in the subjects with natural healthy intact dentions showed lower values, i.e., faster development of the muscular fatigue (31.5 s) compared to the subjects with a pair of new full dentures (44.5 s).

Adult↗
PubMed1990

Transition of myosin isozymes during development of human masseter muscle. Persistence of developmental isoforms during postnatal stage.

Previous results have shown that the adult human masseter muscle contains myosin isoforms that are specific to early stages of development in trunk and limb muscles, i.e. embryonic and fetal (neonatal) myosin heavy chains (MHC) and embryonic myosin light chain (MLC1emb). We wanted to know if this specific pattern is the result of a late maturation or of a distinct evolution during development. We show here that the embryonic and the fetal MHC and the MLC1emb are expressed throughout perinatal and postnatal masseter development. Our results also demonstrate that MLC1emb accumulation increases considerably during the postnatal period. In addition, both the slow MLCs and the slow isoform of tropomyosin are expressed later in the masseter than quadriceps and the fast skeletal muscle isoform MLC3 is not detected during fetal and early postnatal development in the masseter whereas it is expressed throughout fetal development in the quadriceps. Our results thus confirm previous histochemical data and demonstrate that the masseter muscle displays a pattern of myosin and tropomyosin isoform transitions different to that previously described in trunk and limb muscles. This suggests that control of masseter muscle development involves mechanisms distinct from other body muscles, possibly as a result of either its craniofacial innervation or of a possibly different embryonic origin.

Electrophoresis, Gel, Two-Dimensional↗
PubMed2004

Ultrasonographic features of the masseter muscle in female patients with temporomandibular disorder associated with myofascial pain.

OBJECTIVE: The purpose of the present study was to examine ultrasonographic appearances in female patients with temporomandibular disorder (TMD) associated with myofascial pain in comparison with healthy volunteers. STUDY DESIGN: The thickness of the masseter muscle in 25 female patients with TMD was measured at rest and at maximum contraction using ultrasonography. The visibility and width of the internal echogenic bands of the masseter muscle were also assessed and the muscle appearance was classified as 1 of 3 types: type I, characterized by the clear visibility of the fine bands; type II, thickening and weakened echo-intensity of the bands; type III, disappearance or reduction in number of the bands. RESULTS: There were significant differences in the thickness at rest and the increase ratio by contraction between the patient and control groups. The distribution of muscle types showed a significant difference between the 2 groups. CONCLUSION: The ultrasonographic features of the masseter muscle in TMD patients with myofascial pain were clarified and they might be related to muscle edema.

Adolescent↗
PubMed1997

Myositis ossificans traumatica of the masseter muscle: review of the literature and report of two additional cases.

Myositis ossificans traumatica of the masseter muscle is uncommon. The condition is benign and results in reactive heterotopic bone formation, usually producing limitation of opening of the jaws. Radiographic and microscopic examination can confirm the diagnosis. Treatment of myositis ossificans traumatica of the masseter muscle is surgical, with other modalities used when occurring in other muscles of the body.

Adolescent↗
PubMed2000

Identification of matrix metalloproteinases and their tissue inhibitors type 1 and 2 in human masseter muscle.

Changes in masticatory muscle structure and function are either developmental, as seen in anomalies of facial form, or adaptive, as seen during procedures such as orthognathic surgery and functional-appliance orthodontic therapy. Remodelling of muscle extracellular matrix is pivotal in these processes. This turnover is mediated via members of the family of enzymes known as matrix metalloproteinases (MMP) and inhibited by the tissue inhibitors of metalloproteinases (TIMP). The aim here was to investigate the in vivo pattern of expression and distribution of MMPs and TIMPs in masseter muscle of humans with both normal and abnormal facial forms. Masseter muscle biopsies were taken from 10 patients, four with long-face syndrome and six normal controls as confirmed by cephalometry. Immunohistochemical techniques were used to show the pattern and distribution of MMPs and TIMP proteins in the muscle. Zymography of tissue extracts was used to determine the presence of MMP activity. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect the presence of MMP and TIMP-2 mRNA. MMP-1 was expressed around the individual muscle fibres, especially in those fibre surfaces in contact with the interstices of the connective tissue and around blood vessels. MMP-9 staining was less intense and was expressed in the interstices of the connective tissue and around blood vessels. Zymography of protein extracts confirmed that MMP-9 activity was present. MMP-2 and MMP-3 were not expressed in the samples, although MMP-2 mRNA could be detected by RT-PCR and its activity could be detected by zymography. Intense TIMP-1 staining was present around each muscle fibre, in the interstices of the connective tissue and surrounding blood vessels; TIMP-2 mRNA could be detected in all samples. These staining patterns were seen in all biopsies examined and were irrespective of the facial form of the donor. These findings provide evidence that the mechanisms required for matrix remodelling are present in the human masseter muscle.

Adult↗
PubMed1991

Magnetic resonance imaging of the masseter muscle of the rabbit.

Gross anatomy of the masseter muscle was studied in eight rabbits using a 2.34 tesla MRI-device. Anatomy was displayed and assessed consistent with previous dissectional findings. It is concluded that MRI, applied as described in the present study, is suitable for assessment of masseter morphology in experimental studies on the rabbit.

Animals↗
PubMed1999

Effect of 5-hydroxytryptamine infusion on microcirculation in the rabbit masseter muscle measured by laser-Doppler flowmetry.

The aim was to test the hypothesis that 5-hydroxytryptamine (5-HT) influences the microcirculation of the masseter muscle. Rabbit masseters were infused with increasing concentrations of 5-HT (10(-9)-10(-5) M) on the experimental side and with saline on the control side. The effect on microcirculatory blood flow was measured by laser-Doppler flowmetry. The intramuscular temperature was recorded to monitor the influence of tissue temperature. 5-HT infusion resulted in a statistically significant decrease in blood flow at the lowest concentration (10(-9) M) (median; -11.2%: Wilcoxon signed-rank test; p<0.05). At concentrations greater than 10(-9) M, there was no significant change in blood flow. This study shows a decrease of microcirculatory blood flow in the rabbit masseter following 5-HT infusion (10(-9) M).

Animals↗
PubMed1999

[Low energy extracorporeal shockwave therapy (ESWT) for treatment of myogelosis of the masseter muscle].

Patients with functional disorders of the temporomandibular apparatus often show painful myogelosis, especially of the masseter muscle. The cause is hypertonia of the affected muscle. The aim of the presented single-blinded clinical trial was to analyze the effects of low-energy extracorporeal shock waves on patients with pain sensitivity in this region. Participating in the trial were 50 patients with painful, palpable and sonographically evident myogelosis of the masseter muscle. Half of the patients received a single application of 250 impulses of 0.04 mJ/mm2. The second half received an equivalent placebo treatment with the shock-wave impact being inhibited by a neopren insert. It was shown that in 64% of the patients significant alleviation of pain with palpable and sonographically evident softening of the myogelosis could be achieved. In 40% of the patients the therapeutic result could be conserved over a period of 2 weeks. The difference from the placebo group was statistically highly significant. ESWT is thus an easy-to-use, non-invasive method of initial pain therapy for patients with functional disorders. To preserve the long-term therapeutic result, additional functional therapy is nevertheless necessary.

Adult↗
PubMed2001

Correlation of the near-infrared spectroscopy signals with signal intensity in T(2)-weighted magnetic resonance imaging of the human masseter muscle.

The purpose of this study was to compare and contrast blood volume changes transcutaneously measured using near-infrared (NIR) spectroscopy against water signal intensity changes taken from a transverse T(2)-weighted MR image of the masseter muscle in healthy human subjects before, during and after contraction. Eight healthy non-smoking males with no history of chronic muscle pain or vascular headaches participated (mean age: 23.9+/-0.6 years). The MRI data were gathered using a turbo spin echo sequence (TR: 2300 ms; TE: 90 ms; FOV: 188x300 mm; scanning time: 30 s; slice thickness: 10 mm) and the slice level was set at the mid-point between the origin and insertion of the masseter. Intramuscular haemoglobin (Hb) levels and water content of the right masseter muscle were continuously monitored for 2 min before, 30 s during and 15 min after a maximum voluntary clenching (MVC) task. Both the near-infrared and MRI data were baseline-corrected and normalized and mean levels were established and plotted. Plots of the data showed that both near-infrared-based total Hb and T(2)-weighted MRI-based signal-intensity levels clearly decreased during contraction and a clear post-contraction rebound response was evident after the contraction. The near-infrared data were found to be highly correlated with MRI-based signal-intensity data (Pearson's r=0.909, P<0.0001). In conclusion, these data provide powerful evidence that near-infrared data (total Hb), transcutaneously taken from the masseter muscle in humans, will reflect the intramuscular water signal intensity changes seen using a T(2)-weighted MRI imaging method.

Adult↗
PubMed1995

Masseter muscle relaxation rate in volunteers with a myogenous craniomandibular disorder.

Twelve volunteers were investigated to determine their masseter muscle relaxation rate following voluntary contractions. Four of these volunteers were patients diagnosed as having a myogenous craniomandibular disorder. Electromyograms were recorded from the left and right masseter muscles and maximum bite force was recorded in the midline between the incisor teeth. A sustained contraction was maintained at 50% maximum voluntary bite force for 90 s, during which there was a brief relaxation every 10 s. Recordings were continued for a 3 min recovery period. This sequence was then repeated at 25% of maximum bite force. Median power frequencies were calculated from the power spectra for the first and last 3 s of the sustained contractions. Relaxation rates were measured for each brief relaxation during the sustained contraction and for the relaxation from each brief clench during the recovery period. It was found that maximum bite force values were very similar for volunteers in both the patient and control groups. Relaxation rates slowed more and percentage changes in median frequency were greater in the controls than in the patients during the sustained contractions. However, relaxation rates returned to initial levels more quickly in the controls than in the patients.

Adolescent↗
PubMed2004

[Changes of mitochondrial calcium, adenosine triphosphate and adenosine diphosphate contents induced by occlusal trauma in rabbit's masseter muscles].

OBJECTIVE: To study the role of Ca2+ overload and energy metabolism in mitochondria in masticatory muscle dysfunctional induced by occlusal trauma. METHODS: Mitochondrial Ca2+ contents were measured with atomic emission spectrophotometer. Mitochondrial ATP and ADP contents were measured with high performance liquid chromatography. RESULTS: (1) Mitochondrial Ca2+ contents of masseter muscle ipsilateral to metal splint in ten and twenty days' experimental groups and that contralateral to metal splint in twenty days' experimental group increased significantly (P < 0.05). (2) Mitochondrial ATP contents of masseter muscle ipsilateral to metal splint in experimental groups were higher than that in control groups and contralateral to metal splint after twenty days. (3) Mitochondrial Ca2+ contents of masseter muscle ipsilateral to metal splint were significantly negatively correlated to the mitochondrial ATP contents (r = -0.780, P < 0.05). CONCLUSION: Ca2+ overload in mitochondria depresses ATP production, which results in energy metabolism disorder in masticatory muscle cells. It may play an important role in the mechanism that occlusal trauma results in masticatory muscle dysfunction.

Adenosine Diphosphate↗
PubMed2002

Effect of stabilization-type splints on the asymmetry of masseter muscle sites during maximal clenching.

Patients with temporomandibular disorders may present with a cluster of joint and muscle disorders characterized primarily by pain, joint sounds and irregular or deviating jaw function. Maxillary stabilization-type splints represent the best standard therapy, so the purpose of this study was to evaluate changes in local maximal clenching-related asymmetry patterns of masseter muscle sites associated with the immediate 'application of splint therapy' using the diagnostic approach of high-resolution gray-scale ultrasonography. The study included 24 patients who had signs and symptoms of temporomandibular disorders. Ultrasonographic investigation was performed with a linear (B-scan) 7.5 Mhz small-part transducer to visualize the antero-superior, antero-inferior, medio-superior, medio-inferior, postero-superior, and postero-inferior sites of the masseter muscle. To assess local maximal clenching-related muscle asymmetry patterns and to evaluate the respective effect of occluding splints, the 'absolute asymmetry index' was used, with the mean maximum muscle diameter of the respective right and left sides calculated from three consecutive measurements before and after splint insertion. Comparing the values assessed before splint insertion with those after splint insertion revealed a significant decrease in local maximal clenching-related muscle asymmetry values for the antero-inferior masseter muscle site (P < 0.05). The results of this study suggest stabilization-type splints to have a site-specific effect in the immediate reduction of local maximal clenching-related muscle asymmetries. Further studies are warranted to evaluate muscle-site specific effects in patient and non-patient groups and to relate these effects to pre-treatment variables like bite force, preferred chewing side, facial morphology and occlusion.

Adult↗
PubMed1989

[Muscle fiber conduction velocity and frequency parameters of surface EMG during fatigue of the human masseter muscle. 1. Muscle fiber conduction velocity].

The muscle fiber conduction velocity is used as an indication of a localized muscular fatigue or some muscular diseases. The purpose of this study was non-invasively to estimate the conduction velocity of the human masseter muscle using surface electrode arrays. Informed consent was obtained from a group of 8 healthy subjects (24-27 yr) without functional disturbances of the jaws and with natural dentitions. Each subject was asked to perform a brief isometric contraction at 10, 20, 30, 40 and 50% of the maximum EMG amplitude and an endurance of 30 and 50% MVC in the intercuspal position. The myoelectric potential was derived from an adjacent pair of electrode wires and the velocity was estimated by the electrode distance divided by the time delay between two myoelectric signals. The time delay was calculated by the cross-correlation technique. The results obtained were as follows: 1. The muscle fiber conduction velocity slightly increased with contraction force. 2. The exponential reduction in velocity was shown during fatiguing contraction of 50% MVC. 3. The muscle fiber conduction velocity decreased with the time after fatiguing contraction. 4. It was suggested that the conduction velocity of the muscle membrane discharge was an important index of muscular fatigue.

Adult↗
PubMed1987

Modern imaging of the masseter muscle: normal anatomy and pathosis on CT and MRI.

Tremendous advances in diagnostic imaging technology have produced computed tomography (CT) and magnetic resonance (MR) imaging--new ways to depict the normal anatomy and pathosis of the masseter muscle. This article reviews the masseter muscle's normal appearance on CT and MR images and demonstrates the clarity with which CT, in particular, is able to depict soft tissue lesions and neighboring bony involvement. Analysis of the strengths, weaknesses, and availability of these new techniques leads to the conclusion that CT is currently the test of choice for imaging masseteric lesions but that MR shows greater promise for the future.

Adult↗
PubMed2002

Changes in mRNA expression of nicotinic acetylcholine receptor subunits during embryonic development of mouse masseter muscle.

Nicotinic acetylcholine receptors (nAChRs) switch from the embryonic-type (alpha 2 beta gamma delta subunits) to the adult-type (alpha 2 beta epsilon delta subunits), and disappear besides the neuromuscular junctions with the development of trunk and limb skeletal muscles. However, little is known about this process during the embryonic development of masseter muscle. To identify the time course of the nAChR transition from embryonic day (E) 11 to the newborn stage in mouse masseter muscle, we analyzed the expression level of delta, epsilon, and gamma subunit mRNAs by competitive polymerase chain reaction in combination with reverse transcription as well as distribution of delta subunit protein by immunohistochemistry. The nAChR delta subunit mRNA was initially detected at E11, showed an approximately 25-fold increase (p < 0.0001) between E11 and E17, and plateaued thereafter until the newborn stage. Immunostaining for delta subunit was observed in the whole portions of masseter myofibers at E17 and birth, suggesting that the nAChR elimination does not begin even at the newborn stage. The epsilon subunit mRNA initially appeared at E17, and increased in quantity by 144% (p < 0.0001) up to the newborn stage. The quantity of gamma subunit mRNA increased by approximately 240% (p < 0.0001) between E11 and E17, and then decreased by 22% (p < 0.05) from E17 value at the newborn stage. The beginning of the expression of the epsilon subunit mRNA was coincident with the beginning of the decrease in the quantity of the gamma subunit mRNA, suggesting that the nAChR subunit switch begins at E17.

Animals↗