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PubMed1996

Metastatic masseter muscle tumour: a report of a case.

Both primary and metastatic malignancies of the masseter muscle are rare. We report a case of metastatic renal cell carcinoma to the masseter muscle. It was incidentally found as a hypervascular mass in carotid angiography for delineating a recurrent metastatic brain tumour. Prior to surgical removal, intravascular embolization via the left facial artery was performed in order to decrease intra-operative bleeding. The tumour was removed with minimum damage to the muscle fibres by the extraoral method, followed by a transient lower lip palsy. Metastatic intramuscular tumours, which are assumed to be due to haematogenous spread, are generally a sign of poor prognosis.

Angiography↗
PubMed1984

Cumulative electromyography of the human masseter muscle during fatiguing isometric contractions.

Six adult males performed maximum voluntary tooth clenching (MVC) for 10, 20, 30, 40 s and, after 15 min, for 40, 30, 20, 10 s. During the isometric exercises the electrical currents of the masseter muscle were sampled by integrated and cumulative surface electromyography. Subjective masseter fatigue was present after 30 and 40 s of MVC clenching, accompanied by changes in myoelectrical activity. Strength testing of the masseter muscle, before and after endurance testing, showed that the strength increased by a significant 16% following two endurance tests. This observation was explained by a post-tetanic potentiation and/or a differentiated use of motor units in the fatigued muscle. It is concluded that brief MVC isometric activity, or strength testing, is not a reliable measure of fatigue in the masseter muscle when cumulative electromyography is used. Prolonged MVC isometric activity, or progressive endurance testing, monitors reliably the onset and progression of masseter fatigue.

Adult↗
PubMed1994

Immunohistochemical characterization of human masseter muscle spindles.

An enzyme- and immunohistochemical study has been performed on human masseter muscle spindles. Antibodies selective for different myosin heavy chain (MHC) isoforms and M-band proteins (M-protein, myomesin, and MM-CK) were used. The expression of these proteins was determined in the different intrafusal fiber types. Nuclear bag1 and nuclear bag2 fibers expressed predominantly slow-twitch and slow-tonic MHCs. The bag2 fibers in addition contained fetal MHC. Nuclear chain fibers coexpressed embryonic, fetal, and fast-twitch MHCs. The bag2 and chain fibers contained all three M-band proteins, whereas the bag1 fibers contained only myomesin. In general the MHC expression in the human masseter intrafusal fiber types was similar to that previously reported for limb muscles in man as well as for limb and masseter muscles in other species. However, the number of intrafusal fibers per spindle was unusually high (up to 36). This reinforces the idea that masseter muscle spindles have a strong proprioceptive impact during the control of jaw movements.

Adenosine Triphosphatases↗
PubMed2003

Glutamate-evoked pain and mechanical allodynia in the human masseter muscle.

The present study examined the effect of peripheral administration of the excitatory amino acid (EAA) glutamate on the intensity of perceived pain and pressure pain thresholds (PPTs) in healthy young women (n=17) and men (n=18). Two injections separated by 25 min of 0.2 ml, 1.0M glutamate into the masseter muscle produced significantly higher scores of pain on 0-10 cm visual analogue scales (VAS) in women than in men (analysis of variance, ANOVA: P<0.001). There was no significant difference between the VAS scores for the first and the second injections in either men or women. The PPTs determined in the masseter muscle were significantly reduced following the first injection and further significantly reduced after the second injection (ANOVA: P<0.001). Furthermore, the PPTs were reduced to a similar extent in both women and men (maximum 44-56%), suggesting that gender did not influence the process of sensitization. There were no significant difference in VAS scores or PPTs between women taking oral contraceptives (n=9) and those who did not (n=8) (ANOVAs: P=0.709, P=0.153). It is concluded that the VAS scores produced by intramuscular administration of 1.0M glutamate may reflect a gender-dependent activation of nociceptive pathways which, in part, may be mediated through peripheral EAA receptors. The reduction of PPTs in the masseter muscle following administration of glutamate in a concentration of 1.0M may reflect allodynia to mechanical stimuli. This process of sensitization was not gender-dependent. The present results suggest that injection of 1.0M glutamate into the masseter muscle may provide a useful experimental method to test sensitization and efficacy of peripheral EAA receptor antagonists in human subjects.

Adult↗
PubMed2001

Dantrolene counteracts the masseter muscle damage induced by artificial occlusal wear: studies in a rat model.

In previous studies, we showed that the introduction of occlusal alterations to rats results in masseter muscle abnormalities. Here, we investigate whether administration of the muscle relaxant dantrolene to rats with occlusal alteration could counteract the occurrence of such abnormalities. Rats underwent unilateral amputation of molar cusps to cause malocclusion. Some rats received dantrolene (10 mg/kg/day subcutaneously). The masseter muscles ipsilateral to the amputated molars were excised 26 days later. Sham-operated rats were used as controls. The tissue samples were studied by light and electron microscopy and morphometry. Moreover, tissue Ca2+ content, an index of muscle injury, was determined. In the absence of dantrolene, occlusal alteration leads to microvessel constriction, morphologic damage of masseter muscle fibers and blood capillaries, and elevation of tissue Ca2+ content. These changes were nearly abrogated by dantrolene, thus supporting it as a possible new therapeutic tool for the treatment of malocclusion-induced muscle diseases.

Analysis of Variance↗
PubMed1980

The diagnosis and treatment of intramuscular hemangiomas of the masseter muscle.

Two cases of hemangioma of the masseter muscle are presented with a review of the literature. The possibility of an intramuscular hemangioma should be considered in any lateral facial swelling, particularly one anterior to the parotid. Total excision of the hemangioma with a margin of normal muscle is recommended. The approach utilized by the authors is a preauricular incision with elevation of a flap lateral to the parotid gland. This provides an excellent exposure for removal of the tumor with minimal risk to the facial nerve and minimal cosmetic deformity.

Blood Vessels↗
PubMed1984

Traumatic myositis ossificans in the masseter muscle.

Traumatic myositis ossificans in the left masseter muscle of a 25-year-old man is described. The lesion, which extended intramuscularly from the lateral surface of the zygomatic bone to the mandibular angle, was resected by an intraoral approach. The specimen was composed of mature cortical bone in the outer portion and spongy bone, including degenerated muscle fibers and marrow spaces, in the inner portion. At the lower end of the specimen was a sequence of bone formation involving fibrous connective tissue, cartilage, woven bone, and mature lamellar bone with many osteoblasts. Clinicopathologic features of 26 reported cases of traumatic myositis ossificans of the maxillofacial region are reviewed, and the pathogenesis of the disease is discussed.

Adult↗
PubMedDate not supplied

Local anaesthetic bupivacaine alters function of sarcoplasmic reticulum and sarcolemmal vesicles from rabbit masseter muscle.

The effects of local anaesthetics, bupivacaine and lidocaine, on Ca2+ flux behaviour of sarcoplasmic reticulum and on sarcolemmal functions were studied in the rabbit masseter muscle. The experiments were performed on sarcoplasmic reticulum and sarcolemmal vesicles prepared at 1 to 10 days after injection of local anaesthetics or saline into masseter muscle as well as on sarcoplasmic reticulum vesicles prepared from non-treated rabbits (for assessment of the effect on in vitro incubation with local anaesthetics). Bupivacaine potently reduced the efficiency of active sarcoplasmic reticulum Ca2+ transport as evaluated by coupling ratio (Ca2+ transported/ATP hydrolyzed, in the presence of oxalate) at 3 days after the injection; there was only a slight degree of uncoupling of Ca2+ transport from ATP hydrolysis with lidocaine injection. Bupivacaine but not lidocaine, at 3 days after injection, decreased both the apparent permeability of sarcoplasmic reticulum vesicles to Ca2+, determined by measuring net efflux of Ca2+ after stopping pump-mediated fluxes, and the steady-state Ca2+ load in sarcoplasmic reticulum, but had no effect on overall turnover of the Ca2+ATPase. The effects of bupivacaine on apparent sarcoplasmic reticulum Ca2+ permeability and steady-state Ca2+ load were inhibited by a Ca2+ antagonist verapamil. The reduction of Ca2+ uptake of sarcoplasmic reticulum and the protective effect of verapamil were reproduced in unfractionated homogenates prepared at 3 days after bupivacaine injection. In vitro exposure of sarcoplasmic reticulum vesicles to bupivacaine (0.5 to 50 mM) reduced steady-state Ca2+ load in a dose-dependent manner. The observed effect elicited by bupivacaine (25 mM) was partially protected by procaine, an inhibitor of Ca2(+)-induced Ca2+ release from sarcoplasmic reticulum, or by specific closure of the sarcoplasmic reticulum Ca2+ release channel by ryanodine, suggesting the possibility that in vitro exposure of sarcoplasmic reticulum vesicles to bupivacaine may produce an increase in apparent permeability of sarcoplasmic reticulum to Ca2+. In sarcolemma, bupivacaine reduced Na+,K(+)-ATPase and Na(+)-Ca2+ exchange activities at 3 days after injection; the effects on sarcolemmal vesicles were prevented by verapamil. These results suggest that although the effects elicited by bupivacaine injection and the in vitro exposure to bupivacaine on steady-state Ca2+ load of sarcoplasmic reticulum vesicles were similar, the membrane properties of the vesicles from bupivacaine-treated masseter muscles and those from normal untreated muscles may not be the same, which indicates that pure bupivacaine effect is due partly by an effect on ryanodine- and procaine-sensitive Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Anesthetics, Local↗
PubMed1991

Intramuscular hemangioma of the masseter muscle: its characteristic appearance on magnetic resonance imaging.

A 10-year-old girl presented with a 6-month history of right facial swelling. Magnetic resonance imaging (MRI) revealed a tumor in the masseter muscle. On exploration through a preauricular incision, a vascular mass was found located in the lateral aspect of the right masseter muscle. The characteristic MRI appearance of the intramuscular hemangioma of the masseter muscle is shown and the value of MRI for a preoperative differential diagnosis is discussed.

Child↗
PubMed1995

Magnetic resonance spectroscopy of the human masseter muscle in nonbruxing and bruxing subjects.

The masseter muscles of six nonbruxing subjects (five men, one woman) and six bruxing subjects (four men, two women) were assessed during chewing by nuclear magnetic resonance spectroscopy (31P-NMR). The NMR spectra were collected on a GE Sigma 1.5T whole body magnet with a double-tuned 31P/1H surface coil. Two-minute trials of rest/chewing/rest were completed three times. Averaged spectra of inorganic phosphate, phosphocreatine, and three adenosine 5' triphosphate peaks were collected in each trial. Bruxing subjects had a lower concentration of total phosphate and phosphocreatine than nonbruxing (control) subjects at rest. Bruxing subjects increased their inorganic phosphate during chewing significantly less than control subjects. The pH levels during rest and during chewing were similar in both controls and bruxers. These preliminary results suggest that bruxing subjects exhibit an altered phosphate metabolism during rest and exhibit a different phosphate metabolism pattern during chewing as compared to nonbruxing subjects.

Adenosine Triphosphate↗
PubMed2002

Development of sex differences in the rabbit masseter muscle is not restricted to a critical period.

The proportions of muscle fibers of different phenotype in the adult rabbit masseter differ greatly in different sexes. These sex differences are not apparent in young adults, but arise under the influence of testosterone in the males. We examined whether this switch occurred during a critical period of postnatal development. Testosterone was administered to young adults 1, 2, or 4 mo after castration, and also to adult females. Samples of masseter muscle were taken at four monthly intervals after the onset of treatment and examined for the expression of different myosin heavy chain (MyHC) isoforms by using a panel of monoclonal antibodies. Despite the length of androgen deprivation, treatment with testosterone produced a marked MyHC isoform switch from alpha-slow/beta to IIa. This male proportion of fibers of different phenotypes persisted well beyond the return of serum testosterone levels to pretreatment levels. Thus brief exposure to testosterone produces a permanent change in the proportions of masseter muscle fibers of different phenotypes, and the capacity for this change is not restricted to a critical period.

Animals↗
PubMed1990

[Effects of facial nerve denervation on masseter muscle of the rats].

The effects of unilateral facial nerve denervation on the facial growth were studied by physiological and by histochemical examinations, using four- week- old Wistar rats. Two hundred twenty rats were divided into three groups: a control group, a group of subjects which resection of the left facial nerve, and a sham operation group. The rats were killed 1, 5, 10, 30, 60, 90, 120 days later. The superficial and deep masseter muscle fibers on both sides were classified into type I and type IIA or IIB on the basis of myosin ATPase activity and the diameter of these fibers was measured. The masseter muscles were stained with H&E and NADH-TR. Electromyogram recordings were analyzed during the rest position, stretch reflex, voluntary action and eating of solid foods in half of all groups. (1) The face of rats after denervation deviated to the right side, and the maxillo-facial skeleton was affected from the 30th day. (2) In the denervation groups the right side showed higher action potentials than the left side. (3) In the deep masseter muscles near muscle spindle in the denervated groups, the percentage of type I fibers on the right side increased on the 90th day, and that of type IIA fibers decreased on the 30th day. (4) The diameter of the deep masseter muscle fibers, of type I, IIA and IIB increased on the right side. These results prove that facial nerve denervation led to a functional disorder and a transformation of growing direction.

Action Potentials↗
PubMed2000

Three-dimensional morphology of the masseter muscle in patients with mandibular prognathism.

OBJECTIVE: To compare the morphology of the masseter muscle in patients with mandibular prognathism with that of normal subjects. METHODS: Three-dimensional X-ray computed tomography (CT) was performed on 69 patients with mandibular prognathism and compared with 91 normal subjects. The angle of the muscle direction in relation to the Frankfurt horizontal plane and the area and the ratio of length of the short to long axes (s/l ratio) on the section perpendicular to the muscle direction were measured. RESULTS: The mean angle, area and s/l ratio in patients with mandibular prognathism was 76.6 degrees (s.d. 4.4 degrees), 318.3 mm2 (s.d. 77.2 mm2) and 0.312 (s.d. 0.049), respectively. Those of the normal subjects were 65.1 degrees (s.d. 4.4 degrees), 368.3 mm2 (s.d. 97.2 mm2) and 0.393 (s.d. 0.054), respectively. The angle was significantly larger, and the area and s/l ratio were significantly smaller than those of normal subjects (P < 0.001). CONCLUSION: The morphology of the masseter muscle in mandibular prognathism is significantly different from that of normal subjects. Our results may be helpful in evaluating the results of orthognathic surgery.

Adolescent↗
PubMed1987

The amplitude distribution of electromyographic activity in painful masseter muscles during unilateral chewing.

The aim of this study was to investigate whether the amplitude distribution of electromyographic activity (EMG) in terms of muscular load revealed any differences between patients with painful masseter muscles and referents during the chewing of an almond and of gum. The relative masticatory forces of the masseter muscle and the anterior temporal muscle during chewing were calculated by a transformation of the muscular load levels of EMG activity (microV) to load levels of relative masticatory force (%RVC). This was done by regression in reverse of an isometric reference voluntary contraction (RVC) for EMG versus bite force biting on a bite-force sensor. The maximal bite-force values for patients and referents were similar. The relative masticatory force for chewing an almond was higher than that for gum-chewing. The peaks of the relative masticatory forces were similar for both patients and referents. During the chewing of an almond the relative masticatory forces of the masseter muscle below the peak load were higher for patients than referents. During gum-chewing the patients used higher forces than referents for 70% of the total chewing time analysed. This also applied to the anterior temporal muscle when chewing an almond. Estimates of the peak masticatory forces were calculated in newtons.

Adolescent↗
PubMed1993

Masseter muscle reflex evoked by tapping on osseointegrated Frialit implants.

Comparison was made of the masseter muscle reflexes evoked by tapping on osseointegrated single-tooth aluminum oxide implants, and on natural teeth in nine patients. Tapping on eight out of nine patients evoked an inhibitory masseter muscle reflex, whereas tapping on all of the natural teeth evoked an inhibitory reflex. The threshold for this reflex was clearly elevated in implants compared to natural teeth. The pathway for the impulses responsible for this reflex and the clinical implications of the elevated threshold are discussed.

Adolescent↗
PubMed2003

Injection of nerve growth factor into human masseter muscle evokes long-lasting mechanical allodynia and hyperalgesia.

Nerve growth factor (NGF) is a neurotrophic protein with a pivotal role in development and maintenance of the nervous system on one side and inflammatory and neuropathic pain states on the other. NGF causes clear signs of behavioral hyperalgesia in animal models and following intradermal and systemic administration in humans. The present double-blinded, placebo-controlled study was designed to test quantitatively the effect and duration (1h, 1, 7, 14, 21 and 28 days) of NGF (5 microg in 0.2 ml) injected into the masseter muscle. Pressure pain thresholds (PPT) and pressure tolerance thresholds (PTOL) were used as indices of mechanical allodynia and hyperalgesia in the jaw-closing muscles. In addition, perceived pain intensity was assessed by the subjects on a 0-10 numerical rating scale (NRS) with the jaw at rest and in relation to various oral functions (chewing, yawning, talking, swallowing, drinking and smiling). Repeated measures analysis of variance (ANOVA) was used to test for significant effects. Injection of NGF into the masseter muscle was associated with significantly reduced PPT for 7 days (ANOVA: P<0.001) and PTOL for 1 day (P<0.001). Buffered isotonic saline injections into the masseter muscle also significantly lowered the PPT after 1 day but to a significantly smaller extent than the NGF injections (P<0.001) and isotonic saline had no significant effects on PTOL. In contrast, assessment of PPT and PTOL in the non-injected temporalis muscles demonstrated a significant increase after 14-28 days (P<0.001), which may have reflected an adaptation to the test procedure. NRS scores of chewing and yawning were significantly increased for 7 days following NGF injection (P<0.001). Systemic adverse effects were noted in one subject who reported fever and slight discomfort about 8h after the NGF injection. In conclusion, this is the first study to show that injection of NGF into the human masseter muscle causes local signs of mechanical allodynia and hyperalgesia that persist for at least 7 days as well as pain during strenuous jaw movement. The present pain model is safe and may be used to gain further insight into the neurobiological mechanisms of muscle pain and sensitization.

Adult↗
PubMed1998

Effect of local glucocorticoid injection on masseter muscle level of serotonin in patients with chronic myalgia.

The aim of this study was to compare the effects on the level of serotonin (5-HT) in the masseter muscle by intramuscular glucocorticoid (GC) administration in patients with fibromyalgia (FM) and localized myalgia (LM), as well as to determine associated changes in pain, tenderness, and microcirculation. The study comprised 22 patients with pain and tenderness in the masseter muscle region. Ten patients (all women) had FNI, and 12 (1 man and 11 women) had LM involving the temporomandibular system. The patients were examined clinically and by microdialysis at 2 visits 2-3 weeks apart and received local glucocorticoid treatment at the first visit. The ratio (S1/S2) between the initial level of 5-HT (S1) and steady state level (S2) was used as a relative measure of the intramuscular release of 5-HT. This ratio decreased significantly after treatment in the FM group. In the FM group there was also a negative correlation regarding changes between visits of 5-HT and changes of intramuscular temperature. In the LM group there was a negative correlation regarding changes between visits of 5-HT and changes of pressure pain threshold and pressure pain tolerance level. This study indicates that there is a reduction of the ratio between initial 5-HT and steady state level in the painful masseter muscle after intramuscular GC administration to FM patients, a reduction not present in the LM patients. In addition, 5-HT seems to be involved in the modulation of local muscle microcirculation in FM patients and in hyperalgesia in LM patients.

Adult↗
PubMed2006

Intramuscular vascular malformation of the masseter muscle presenting with turkey wattle sign.

Intramuscular vascular malformations are unusual tumors in the head and neck region. Less than 1% of vasoformative tumors throughout the body occur in skeletal muscle; 15% of them arise in head and neck musculature. Masseter muscle is the most frequent site for such vascular malformations; it accounts for approximately 5% of all intramuscular vascular malformations in the head and neck region. A case of unusual intramuscular vascular malformation of masseter muscle is described and the diagnosis and management of these tumors is discussed.

Adult↗