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PubMed1989

Clinical significance of isometric bite force versus electrical activity in temporal and masseter muscles.

Bite force and activity in temporal and masseter muscles during biting and chewing were recorded in 19 control subjects and 23 subjects with symptoms and signs of functional disorders of the craniomandibular system. The entire group comprised 13 men and 29 women, 14-63 yr of age. Maximal unilateral bite force was 480 Newton (N) in control subjects and 387 N in patients, with corresponding bilateral values of 347 N and 230 N. At predetermined levels of contraction, temporalis and masseter activity were linearly related. Correlations of bite force and activity in short static contractions were significant with respect to unilateral, but not to bilateral force measurements. Only in the masseter muscle was strength of dynamic contractions during chewing significantly correlated to bite force. With the present method it was demonstrated that unilateral bite force is a simple clinical indicator of mandibular elevator strength as a whole, but inadequate to disclose asymmetric conditions. During isometric contraction, relative strength of electromyographic activity fairly accurately imaged the output of mechanical activity.

Adolescent↗
PubMed1998

Propofol reduces succinylcholine induced increase of masseter muscle tone.

PURPOSE: Succinylcholine is known to increase the tone of the masseter muscles. As excessive jaw tension may complicate rapid sequence induction, we investigated three induction techniques, all including the use of succinylcholine, with respect to masseter muscle tone, neuromuscular blockade, intubation conditions, and time course of intubation. METHODS: Sixty adult patients were allocated to one of three induction groups: Group THIO received 5 mg.kg-1 thiopentone, Group THIO/ATR received 5 mg.kg-1 thiopentone plus 0.05 mg.kg-1 atracurium for precurarization, and Group PROP received 2.5 mg.kg-1 propofol. All patients received 3 micrograms.kg-1 fentanyl and 1.5 mg.kg-1 succinylcholine. Time for induction of anaesthesia was recorded, and, after inserting a Grass Force Transducer between upper and lower incisors, jaw tone and the time course of jaw tension was recorded before and after the administration of succinylcholine. RESULTS: No differences in the onset of sleep were observed among the three groups (Group THIO 33 +/- 2 sec: THIO/ATR 30 +/- 2 sec: PROP 35 +/- 2 sec, mean +/- SE). Masseter preloads following induction of anaesthesia were similar in all three groups (THIO 16.4 +/- 2.1 N: THIO/ATR 15.1 +/- 2.0 N: PROP 12.7 +/- 1.6 N). However, after administration of succinylcholine, the increase in masseter tone was less in Groups PROP (5.0 +/- 1.1 N) and THIO/ATR (6.4 +/- 2.1 N) than in Group THIO (12.4 +/- 3.0 N; P < 0.05). CONCLUSION: Jaw tension after administration of succinylcholine is influenced by the choice of induction agent. The increase of masseter muscle tone is lower following propofol or thiopentone/atracurium induction than with thiopentone alone.

Adolescent↗
PubMed2002

Ultrasonographic assessment of local cross-sectional dimensions of masseter muscle sites: a reproducible technique?

Local cross-sectional dimensions (LCSDs) of masseter muscle sites may now be measured non-invasively using ultrasonography. The purpose of the present study was to determine (i) whether the muscle site may affect LCSD measurements and (ii) whether measurements made at identical sites may be reproducible. The study included 17 patients who had signs and symptoms of temporomandibular disorders (TMD). Bilateral 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. Measurements were made in two sessions with a time interval of at least five minutes. Data were analysed for reproducibility by using the intraclass correlation coefficient (ICC) and the method error (ME). Muscle site had no significant effect on muscle measurements (P = 0.090). Measurements from the various side-related sites did not differ significantly (P = 0.425). Measurements recorded at a given site were consistent across the testing sessions (P = 0.605). The muscle site with highest reproducibility was the medio-inferior site (ICC = 0.92; ME = 6.4%). The data suggest that ultrasonography is a reproducible method for measuring LSCDs of the masseter muscle.

Adolescent↗
PubMed1995

Intramuscular cavernous hemangioma of the masseter muscle.

Intramuscular hemangioma is relatively uncommon and frequently misdiagnosed, and even rarer in the head and neck region. The masseter muscle is the most frequent site for such hemangioma in the head and neck. A retrospective chart-review of intramuscular hemangioma in Keelung Chang Gung Memorial Hospital from 1983 through 1992 revealed the incidence of masseter muscle hemangioma is approximately 8% of all intramuscular hemangioma. Because of the rarity of these tumors, their vague presentations, inaccurate preoperative diagnosis and inappropriate surgical planning are common problems. This paper described five hemangiomas involving the masseter muscle with a review of the current literature on masseter muscle hemangioma.

Adult↗
PubMed1997

Postnatal development of the masseter muscles in the Japanese field vole Microtus montebelli, with special attention to differentiation of the fast-twitch oxidative fiber.

Postnatal development and differentiation of the masseter muscles consisting only of fast-twitch oxidative (FO) fibers in the adult Japanese field vole Microtus montebelli were studied using histochemical and electron microscopic techniques. The masseter muscles were composed of myotubes and muscle fibers at day 0 (birth day). Most muscle cells showed the strong reaction for myosin ATPase after both alkaline and acid preincubations. For NADH-dehydrogenase (NADH-DH), small granular diformazan deposits were recognized in the sarcoplasm. Afterwards, the masseter muscles consisted of myofibers and satellite cells at day 5. For myosin ATPase, weakly-reactive fibers after acid preincubation (fast-twitch fibers) increased in number. For NADH-DH, granular diformazan deposits in all the myofibers increased in size. Since all the myofibers had numerous sarcoplasmic reticula, and they reacted strongly after alkaline preincubation and weakly after acid preincubation for myosin ATPase at day 10 when the young start to take solid food, it seems that the masseter muscles become contractive fast. At day 15 (before weaning), all the myofibers showed the adult-like strong reaction for NADH-DH and had numerous well-developed mitochondria, thus they acquired the ability of the fast and sustained contraction. It is accordingly considered that the masseter muscles of the vole mature in a short time after birth because of adaptation for herbivorous food habit.

Adaptation, Physiological↗
PubMed2004

Effects of diet consistency on the expression of insulin-like growth factors (IGFs), IGF receptors and IGF binding proteins during the development of rat masseter muscle soon after weaning.

A soft diet facilitates the development of faster-type fibres in rat masseter muscle in the 9 days after weaning compared with a hard diet. To determine whether insulin-like growth factors (IGFs), IGF receptors (IGFRs) and IGF binding proteins (IGFBPs) are involved in this fibre-type alteration, the expression of myosin heavy chain (MHC), IGF, IGFR and IGFBP mRNAs in the masseter muscle of rats fed a hard or soft diet for 9 days after weaning was analysed using competitive, reverse transcriptase-polymerase chain reaction. A soft diet decreased the expression of MHC IIa (slower type) by 70%, but increased the expression of MHC IIx (intermediate type) and IIb (faster type) by 80 and 582%, respectively, compared with a hard diet. These findings verified that a soft diet facilitates the development of faster-type fibres in rat masseter muscle compared with a hard diet. A soft diet induced reductions of 25-76% (P < 0.05-0.01) in the expression of IGF-I, IGF-II, IGFR2, IGFBP4 and IGFBP6 compared with a hard diet, but induced a 25% (P < 0.05) increase only in expression of IGFBP3. These findings suggest that the changes in expression of IGF-I, IGF-II, IGFR2, IGFBP3, IGFBP4 and IGFBP6 are associated with the fibre-type alteration of rat masseter muscle in response to diet consistency soon after weaning.

Animals↗
PubMed1991

The inferiorly based masseter muscle flap: anatomical basis for its use in head and neck reconstructive surgery.

The aim of this study was to investigate and elucidate the anatomical basis for the use of the inferiorly based masseter muscle flap in the reconstruction of oropharyngeal defects after ablative surgery. The anatomy of the masseter muscle, with particular emphasis on its blood supply, was studied using plain and coloured resin injected dissections and a series of digital subtraction angiograms and external carotid arteriograms. Both techniques were demonstrated to be reliable and effective means of anatomical investigation of blood vessels. The vascular anatomy of the masseter muscle and the anatomical and angiological results as well as a case report are described. The masseter muscle, when used as an inferiorly based flap, provides the necessary bulk for reconstruction of moderate size defects in the lateral border of the tongue, posterior floor of the mouth, retromolar trigone, anterior tonsillar pillars and lateral pharyngeal wall. Although the masseter muscle has small dimensions, it offers a reliable method of reconstruction in selected defects without the disadvantages of cosmetic and functional loss.

Angiography, Digital Subtraction↗
PubMed1996

Masseter muscle thickness in growing individuals and its relation to facial morphology.

It is widely accepted that an interaction exists between masticatory muscle function and craniofacial growth. In adults, correlations have been found between facial dimensions and jaw-muscle cross-sectional area, and between facial dimensions and masseter muscle thickness. Little is known about growth of the human masticatory muscles and its relation with facial dimensions at different ages. In 329 Greek individuals, aged 7-22 yr, masseter muscle thickness was measured by ultrasonography. Muscle thickness was related to age, stature and weight, and to facial dimensions, measured by means of anthropological calipers. Muscle thickness was statistically assessed by univariate analysis of variance, after the males and females had been divided into three age groups. Facial dimensions were assessed by multivariate analysis of variance, age being considered as a covariate. The relation between muscle thickness and facial dimensions was subjected to stepwise multiple regression analysis. Masseter muscle thickness increased with age in both sexes. No differences were found between the left- and right-hand side. For each age group (and corrected for stature and weight), males had significantly thicker masseters than females (p < 0.01). Variation in muscle size and facial dimensions mainly coincided with variation in age, stature and weight. Apart from these, muscle thickness showed a significantly negative relation with anterior facial height and mandibular length, and a significantly positive relation with intergonial width and bizygomatic facial width.

Adolescent↗
PubMed1990

[Effects of sevoflurane and enflurane on isometric tension and maximum velocity of shortening in glycerinated guinea pig masseter muscles].

To study the effects of inhalation anesthetics on the contractile system of masseter muscles, the Ca2+ concentration-isometric tension relationship and the maximum velocity of shortening were investigated in glycerinated guinea pig masseter muscles under the presence and absence of sevoflurane (10 mg% and 100 mg%) or enflurane (10 mg% and 100 mg%). Relative isometric tensions increased sigmoidally with an increase in Ca2+ concentration in all groups. K1/2 (pCa at the half maximum activated tension) was 6.53 in the control (absence of the anesthetics) and about 6.70 in the experimental groups under anesthetics regardless of the concentrations of anesthetics. The isometric tensions at higher Ca2+ concentrations were reduced by enflurane dose-dependently. They were also reduced by the low concentration of sevoflurane but increased by its high concentration. The maximum velocity of shortening was not influenced by these anesthetics (100 mg%) as far as the Ca2+ concentration was constant (pCa 6.36 or 5.94). These results suggest that in the masseter muscle, sevoflurane and enflurane alter the Ca2+ affinity in troponin C for actin filaments without changing the cross-bridge turnover rate.

Anesthetics↗
PubMed1989

Characteristics of responses in the trigeminal subnucleus caudalis and adjacent reticular formation evoked by the stimulation of the masseter muscle.

Our previous study reported that the afferents to the spinal trigeminal nucleus from the masseter muscle were predominantly of A-delta range fibers having fast conducting-low threshold and slow conducting-high threshold. In the present study, further experiment was undertaken to obtain more definite information on the central transmission of muscle pain. When the electrical stimulation was delivered to the masseter muscle of rat, the evoked potentials with a shorter latency (the S-response) or longer latency (the L-response) were recorded from the caudal part of the spinal trigeminal nucleus. In both the S- and the L-responses, the relationship between the amplitudes of the responses and the stimulus intensity almost followed the power function with the exponent of about 3.4 and 4.0, respectively. The stimulus intensity range of the S-response, in which the power function was formed, was wider than that of the L-response. The most of the S-response were recorded from the trigeminal subnucleus caudalis and adjacent reticular formation, whereas the recording sites of the L-response were located mainly in the trigeminal subnucleus caudalis. These results suggest that the trigeminal subnucleus caudalis and adjacent reticular formation are an important portion of the afferent projection areas and of the modulator system of pain sensation from the masseter muscle.

Afferent Pathways↗
PubMedDate not supplied

Magnetic resonance imaging of the masseter muscle: a preliminary genetic study in monozygotic and dizygotic twins.

Magnetic resonance images of the head were taken in five monozygotic and seven dizygotic twins in order to calculate bilaterally masseter muscle cross-sectional areas and total volume. Comparing correlation coefficients between cotwins, genetic influences could be expected for maximal cross-sectional area but not for volume measurements. Model fitting revealed that additive genetic factors explained 93.9% of the variance for the left and 82.4% for the right maximal masseter muscle cross-sections. It is anticipated that while the number of masseter muscle fibers is under strong genetic control, the length of individual fibers can be influenced by specific environmental factors. In the second part of the investigation, cephalometric measurements from lateral headplates were compared with these masseter muscle values in 10 twin pairs. Only three of the 15 angular and five (three vertical, one transversal, and one sagittal measurement) of the 20 linear measurements were significantly correlated with masseter muscle values.

Face↗
PubMed2006

Influence of intramuscular nerve growth factor injection on the response properties of rat masseter muscle afferent fibers.

AIMS: To investigate whether local administration of nerve growth factor (NGF) decreases the mechanical threshold (MT) of putative nociceptive masseter afferent fibers as part of its mechanism of mechanical sensitization. METHODS: Electrophysiologic recordings were made from masseter afferents and a randomized, blinded approach was used to test the effects of intramuscular injection of NGF (2.5 or 25 microg/mL) into the rat masseter muscle on the MT of masseter afferents (n=65) and plasma protein extravasation. RESULTS: The plasma protein extravasation data and electrophysiological recordings indicated that rat NGF injection was not inflammatory and did not evoke afferent discharge or induce mechanical sensitization (as reflected in a decreased MT) in masseter afferents in either male or female rats. To investigate whether the lack of effect of NGF injection might be due to differences between human and rat NGF, additional experiments with human NGF injection (25 microg/mL) were undertaken. Intramuscular injection of human NGF into the rat masseter muscle also failed to evoke afferent discharges; however, it did decrease the MT of masseter afferent fibers. CONCLUSION: The finding that neither rat nor human NGF excited putative nociceptive masseter afferent fibers is consistent with a previous report that intramuscular NGF injections are not acutely painful in human subjects. The ability of human NGF injection into the rat masseter muscle to induce afferent mechanical sensitization suggests that this experimental approach may be useful for the study of peripheral mechanisms of myofascial pain and tenderness associated with temporomandibular disorders.

Afferent Pathways↗
PubMed1994

Masseter muscle hyperactivity and myofascial pain dysfunction syndrome: a relationship under stress.

Myofascial pain dysfunction syndrome (MPD) of the temporomandibular joint (TMJ) is a psychophysiological disorder that develops because of hyperactive muscles of mastication. Ten women meeting criteria for MPD and 12 symptom-free women participated in the study. The rationale for this study was to observe cardiovascular and masseter muscle changes during four contiguous experimental periods: baseline/adaptation, reaction time, recovery, and relaxation. MPD patients showed less masseter muscle activity and higher heart rates at baseline than controls. Controls had significantly higher masseter EMG activity during reaction time. Both groups showed significant elevation in masseter muscle activity and heart rate over the 14-min reaction period. MPD patients' recovery from stress was equivalent to controls' for both heart rate and masseter muscle activity. MPD patients exhibited significantly slower reaction times than controls. The results suggest that masseter muscle hyperactivity may not account for the development and maintenance of MPD.

Adult↗
PubMed2002

Antero-posterior activity changes in the superficial masseter muscle after exposure to experimental pain.

The aim of this randomized, controlled, double-blind study was to examine how the activation pattern of the masseter muscle changes during natural function when experimental pain is induced in a discrete anterior area of the muscle. In 20 subjects, three bipolar surface electrodes and three intramuscular fine-wire electrodes (antero-posterior mapping) were simultaneously attached above and in the right masseter muscle to record the electromyographic (EMG) activity during unilateral chewing before and after infusion of a 0.9% isotonic and 5% hypertonic saline bolus in the anterior area of the muscle. The activity of the contralateral masseter muscle was registered by surface electrodes. In addition, the development of pain intensity was quantitatively measured with a numerical rating scale (NRS). While both saline concentrations caused pain, the hypertonic solution evoked stronger pain. The experiments also provided evidence of a significant although differential activity reduction of the ipsilateral masseter muscle in the antero-posterior direction. The activity reduction decreased with increasing distance from the location of the infusion. The results support the idea that the strategy of differential activation protects the injured muscle while simultaneously maintaining optimal function.

Adult↗
PubMed1999

The onset of neuromuscular block at the masseter muscle as a predictor of optimal intubating conditions with rocuronium.

After an intubating dose of rocuronium satisfactory intubating conditions are achieved before the onset time at the adductor pollicis. We examined the possibility that measurement of the relaxation of the masseter muscle is a more appropriate guide when determining the intubating time. Simultaneous accelerometry with a 0.1-Hz single twitch stimulation of the chin and thumb was performed in 20 patients after 0.6 mg kg-1 rocuronium. We observed a significantly more brief mean lag time and onset time at the masseter muscle (22.5 and 61 vs. 32.5 and 160 s). The corresponding mean relaxation at the onset time was also significantly more pronounced at the masseter muscle (99.6 vs. 97.6%). A mean onset time at the masseter muscle of 61 s as produced by rocuronium corresponds clinically with excellent or good intubating conditions. From these results, we suggest that measurement of the onset time of muscle relaxation at the masseter muscle appears to be a better predictor of good intubating conditions than measurements made using the adductor pollicis muscle after administration of rocuronium.

Adolescent↗
PubMed2001

Magnetic resonance spectroscopy of the masseter muscle in different facial morphological patterns.

The aims of this study were (1) to develop a reliable noninvasive method to evaluate the masseter muscle metabolism, by using (31)P-magnetic resonance spectroscopy, and (2) to evaluate the metabolic profile of the masseter muscle in subjects with various facial patterns. The maxillary-mandibular relationship, which varied from hypodivergent to hyperdivergent, was measured on lateral cephalograms of 20 adults, 22 to 35 years of age. (31)P-spectra were acquired from the masseter muscle at rest with a custom-made, single-turn, double-tuned, 3 x 5-cm oblong surface coil. The inorganic phosphate to phosphocreatine (Pi/PCr) ratios were measured and compared in relation to vertical and sagittal cephalometric measurements. A statistically significant (R(2) = 0.65, r = 0.81, P = .001) relationship was found between Pi/PCr ratio and the palatal-to-mandibular plane angle. As the maxillary-to-mandibular divergence increased, the Pi/PCr ratio decreased. This correlation suggests that muscles with a higher Pi/PCr ratio have a higher resting metabolic activity than those with a lower Pi/PCr ratio. Consequently, these muscles may keep bone under more tension and influence its growth in a more horizontal direction. Another possible explanation of the results is that the fiber type composition of the masseter muscle varies with facial morphology.

Adult↗
PubMed1984

Effects of topical cooling on isometric contractions of the human masseter muscle.

Six adult males performed tooth clenching for 10 and 80 s at maximum voluntary contraction strength (MVC). Motor activity in the right and left masseter muscles was monitored by surface electromyography. Local temperatures of both cheeks were monitored by a thermocouple. MVC activity for 80 s induced pain and fatigue in both muscles; 10 s of clenching caused no muscle discomfort. Ice, subsequently applied to the right cheek for 30 min, lowered the temperature of the cheek and masseter muscle. The isometric MVC exercises were then repeated. During 10 s of isometric contraction, MVC motor activity in the cooled masseter muscle was significantly increased by 29 per cent; that of the non-cooled contralateral muscle was insignificantly reduced by 12 per cent. During 80 s of clenching, MVC motor activity in the cooled muscle was significantly increased by 30 per cent; that of the non-cooled muscle was insignificantly reduced by 4 per cent. MVC activity for 80 s by the cooled muscle caused no pain and fatigue, but the discomforts continued in the non-cooled muscle. Increased MVC alpha motor activity in the cooled masseter muscle might have resulted from motor facilitation that was mediated by cutaneous, muscular or mucosal cold receptors, or it might have been due to the absence of pain and fatigue.

Adult↗
PubMed2003

Reliability and temporal variation of masseter muscle thickness measurements utilizing ultrasonography.

Muscle thickness may now be measured in the clinic by ultrasonography. The purpose of this study was to test (i) whether the position of the transducer on the muscle affects muscle thickness measurements and (ii) whether measurements from identical locations vary over time. Muscle thickness of one masseter muscle side was measured in each of 30 volunteers. Measurements were recorded at five different locations on the lateral surface of each muscle. Four measurement sessions were performed, and two sets of measurements were recorded at each session. Spatial position of the transducer had a clear effect on the muscle thickness measurements (P < 0.0001). Measurements made at the most upper and middle level were less and greater (P < 0.0001), respectively, than those made at the upper, lower, and most lower levels. Measurements from various positions did not differ (P > 0.05) when made at the same level. Masseter thickness measurements recorded at a given site were consistent across all of the testing sessions (P=0.575). The data suggest that reliable interpretation of longitudinal measurements of masseter thickness obtained with ultrasonography requires accurate repositioning of the transducer. Ultrasonography may be used to investigate the effect of specific treatment modalities on masseter thickness measurements.

Adult↗