[EFFECT OF SOME CHOLINESTERASE-REACTIVATORS ON THE ACTIVITY OF STRIATED MUSCLES IN VIVO (THE MASSETER MUSCLE IN THE RAT)].
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Cholinesterase Reactivators↗
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Response characteristics an classification of muscle spindles of the masseter muscle in the cat.
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Afferent Pathways↗
[Examination of coordination of masseter muscle activity].
The coordination of masseter muscle contraction is inseparably wrapped up in the occlusal elements. This study measured bilaterally the masseter muscle activity of 22 subjects without temporomandibular joint disease. The EMG recordings of the left and the right masseter muscles were repeated 20 times to test symmetry, reproducibility and appearance of silent periods. In 6 subjects the beginning of the muscle contraction showed laterality characteristics depending on handedness. The complex processes of recorded mandibular movements showed more biological variations than the recording patterns of occlusal indicator foils may disclose. That indicates the possibility of pseudocontact markings. The occluding surfaces therefore should allow free mandibular movements.
Adult↗
Influence of an occlusal splint on integrated electromyography of the masseter muscles.
In order to examine the effect of an occlusal splint on the integrated electromyography (EMG) of the masticatory muscles, EMG of bilateral masseter muscles of 23 patients with temporomandibular joint disturbance syndrome (TMJDS), with and without an occlusal splint, was measured and integrated on line during maximum clenching. It was found that the integrated myoelectrical value of the masseter muscle on the involved and non-involved side was reduced with the occlusal splint. The absolute difference between integrated myoelectrical values in the left and right masseter muscles was reduced with an occlusal splint, but the relative difference remained virtually unchanged. These results indicate that the occlusal splint can decrease masseter muscle activity and thus exert a therapeutic effect.
Adult↗
Growth of the masseter muscle in rhesus monkeys (Macaca mulatta).
The growth of the masseter muscle in eight infant, juvenile, and adolescent female rhesus monkeys (M. mulatta) was examined over a 2.5 year period using serial radiographic cephalometric techniques with the aid of radiopaque muscle markers. The radiopaque markers, which are composed of small pieces of root canal broach inserted into the muscle belly, make it possible to determine longitudinal masseter muscle growth as well as migration of the masseter muscle relative to the mandible. It was found that the masseter muscle increased in length by 64% during the total growth period, most of which occurred between 6 and 18 months of age. Relative to the cranium, the masseter muscle grew markedly inferiorly and only slightly posteriorly. Relative to the mandible, the masseter migrated in a posterior and slightly superior direction, keeping pace with the ramus and condyle as they grew posteriorly and posterosuperiorly throughout the study period. It was concluded that: 1) radiopaque muscle markers are a valuable tool for analysis of muscle growth and alteration of muscle location; 2) the masseter muscle in the rhesus monkey undergoes elongation, probably due to addition of sarcomeres at the fiber-tendon junctions; and 3) posterior migration of the masseter muscle relative to the corpus of the mandible, probably due to the nature of its periosteal attachment, results in a stability of the anteroposterior position of the masseter muscle despite the anterior displacement of the mandible.
Aging↗
[Arterial supply to the masseter muscle in the rat].
Eighteen rats (thirty-six sides) were injected with red latex into the peripheral arteries through the left ventricle in the heart and fixed in 10% formalin to demonstrate the arterial architecture. According to the method of Yoshikawa et al. who proposed the lamination theory of this muscle, the latex injected specimens were dissected under a stereoscopic microscope. The masseter muscle in the rat was distributed by the masseteric branches of the facial, external carotid and dorsal branch of the infraorbital arteries as well as the transverse facial, masseteric and buccal arteries. This finding was essentially the same as observed on other species which included the dog, cat, crab-eating monkey, rabbit, cow and horse. However, the origin, course and distribution of the posterior deep temporal and masseteric arteries in the rat were considerably different from those of other species. Furthermore, since the way of development of the arteries and the subdivided muscles of the masseter muscle varies among species, the relationships between these arteries and the subdivided muscles seem to differ to some extent from species to species. Outline of the arterial system of the lateral aspect in the rat's head was shown in Fig. 1. The arteries and masseteric branches which were distributed to the subdivided muscles of the masseter muscle in the rat were as follows. 1) The first and second superficial and intermediate masseter muscles were distributed by the masseteric branches of the facial and external carotid arteries as well as the transverse facial, buccal and masseteric arteries. 2) The anterior portion of the deep masseter muscle was supplied by the masseteric branch of the facial, the masseteric and the buccal arteries. 3) The posterior portion of the deep masseter muscle received only the masseteric artery. 4) The maxillomandibular muscle was vascularized by the masseteric branch of the dorsal branch of the infraorbital and the buccal arteries. 5) the zygomaticomandibular muscle included only the masseteric artery.
Animals↗
Effect of maturation on 31P magnetic resonance spectroscopy of the rabbit masseter muscle.
This work studies the dynamic metabolic changes of the rabbit masseter muscle during post-natal development. The composition and proportion of oxidative and glycolytic muscle fibers alter during maturation. The masseter muscle, as most muscles of the craniofacial region, exhibits unusual development in composition of isoforms of myosin. The effect of this unusual composition on the dynamic metabolic properties of the masseter muscle have not been assessed. The metabolism of the rabbit masseter muscle was studied by means of 31P-nuclear magnetic resonance (NMR) spectroscopy. Contraction was elicited by electrical stimulation of the muscle in the anesthetized animal. Five animals were studied at 8 weeks and 24 weeks so that both the juvenile and adult stages could be evaluated. The dynamic biochemical changes in the masseter muscle were studied by the analysis of NMR spectra. A single-turn surface coil (copper) was used, and the original signal was treated with Fourier transforms to obtain 31P spectra. The low signal-to-noise ratio required averaging 16 acquisitions (acquisition time = 400 msec, repetition rate = 1.8 sec) in 30 sec and then obtaining continuous spectra for 27 min. Each averaged spectrum demonstrated five peaks: inorganic phosphate (Pi), creatine phosphate (PCr), and three peaks related to adenosine triphosphate (ATP). The protocol involved recording an initial three-minute rest period, stimulating the muscle at 5 Hz for 3 min twice, separated by three-minute rest periods, and stimulating the muscle at 50 Hz twice for 3 min separated by rest periods. The Pi/PCr ratio increased significantly in the adult masseter during both 5-Hz stimulations, evoking twitching, and the first 50-Hz stimulation, evoking tetany (repeated ANOVA, P < 0.05). The resting pH (6.96 +/- 0.13) was significantly lowered during both twitching (6.85 +/- 0.10; P < 0.0038) and tetany (6.55 +/- 0.13; P < 0.0001), but only in the adult masseter muscle. These finding suggest that the adult masseter muscle possesses more glycolytic fibers as it modifies its metabolism during postnatal development.
Adenosine Triphosphate↗
Adaptation of the lateral pterygoid and superficial masseter muscles to mandibular protrusion in the rat.
It has been suggested that protrusion of the mandible results in an alteration of the functional activity of the lateral pterygoid muscle. If this is true, however, it is unclear whether this altered muscle function is a transient phenomenon with no long-term effect or whether it results in structural and functional adaptation of the involved musculature. The purpose of this study was to determine whether or not physiologic and metabolic changes take place within two jaw-protruder muscles--the lateral pterygoid muscle and the superficial masseter muscle--in rats after treatment with a protrusive appliance. Thirty 45-day-old male Sprague-Dawley rats were divided equally into experimental and control groups. The experimental animals wore bonded protrusive-type appliances for 2 weeks. Histochemical analysis of muscle fiber types and in vivo whole-muscle contractile-property analysis were used to evaluate structural and functional muscle adaptations. Mandibular length was slightly but significantly greater in the experimental group, indicating that the protrusive appliance had the expected positive effect on mandibular growth. Histochemically, the lateral pterygoid muscle in the experimental group exhibited a significantly greater area occupied by type I fibers at the expense of type IIb fibers. The superficial masseter muscle exhibited a significantly greater percentage of areas for both type IIa and type IIb fibers in the experimental group. Contraction time (TPT) increased in both muscles; that is, the muscles became slower. The histochemical and contractile-properties data indicate that the protrusive appliance caused the lateral pterygoid muscle to become more active with respect to tonic (postural) activity, whereas the superficial masseter muscle became more active phasically.
Adaptation, Physiological↗
Masseter muscle hypertrophy. Aetiology and therapy.
Masseter muscle hypertrophy (MMH) is most probably a congenital, genetically determined anomaly. Thus we should refer to it as hyperplasia rather than hypertrophy of the masseteric muscle. Excision of the internal layer of the masseter muscle and reduction of the thickened bone in the region of the mandibular angle, via an intraoral approach, is the treatment of choice. Immediately after surgery it is necessary to apply a fixed compression bandage to the masseteric region in order to obliterate dead space which would otherwise be filled by a haematoma which in turn leads to prolonged postoperative trismus. After removal of the bandage it is necessary to institute mouth opening exercises. Very good esthetic and functional results were achieved.
Adult↗
[Muscle action potential and masticatory rhythm of anterior temporal and masseter muscles in children and adults].
For the investigation of the functional change of the masticatory muscles along with growth and development, electromyographic evaluation was carried out. The subjects were 6 children (5 males and 1 female) with full deciduous dentition (Hellman's dental age IIA) aged 4.5 +/- 0.2 years and 6 adults (4 males and 2 females) with full permanent dentition aged 27.7 +/- 3.8 years. EMG signals were recorded bilaterally by means of bipolar silver surface electrodes from the anterior temporal and masseter muscles when the subjects were chewing chewing gum or performing maximum clenches in intercuspal position. The cumulative power values from 62.5 to 1000 Hz in the EMG power spectrum during chewing or clenching were calculated as the muscle action potential. The ratio of the action potential of each muscle to the total action potential of four muscles were analyzed. Masticatory rhythm during chewing was analyzed by means of the time parameter (duration, interval and cycle) and their coefficients of variation. The results were as follows: 1. In children the temporal muscles predominated in chewing and clenching, whereas in adults there were three types with Temporal muscles predominating, Masseter muscles predominating and both muscles sharing equally. 2. No statistically significant differences between children and adults were observed in the duration, interval and cycle. 3. In adults the coefficients of variation of the duration, interval and cycle were smaller and the masticatory rhythm was more stable than in children.
Action Potentials↗
Masseter muscles electromyography study of individuals with and without malocclusion during dental clenching.
The present study had as an objective to verify the electromyographic activity of the masseter muscles during intercuspal maximal clenching in individuals with and without malocclusion. For such purpose, 37 individuals participated, constituting three distinct groups according to the classification of the occlusion: 9 individuals with clinically normal occlusion (G1), 17 individuals with Angle Class I malocclusion (G2) and 11 individuals with Angle Class II division 1 malocclusion (G3). Allparticipants were female, between the ages of 20 years, 7 months to 30 years, 8 months, with permanent natural teeth. The selection of the individuals was made with the application of a specific protocol, being complemented with an oral clinical myofunctional exam. The activity of the bilateral muscle masseter was investigated, in its superficial portion, by means of electromyographic evaluation with surface electrodes. Three consecutive intercuspal maximal clenching were recorded. The results showed that there was not significant statistical difference from the eletromyographic activity between the three groups. The conclusion was that the malocclusion did not interfere in the eletromyographic activity of the masseter muscles.
Adult↗
Magnetic motor evoked potentials (MEPs) in masseter muscles.
Electromyographic responses of the masseter muscles and orbicularis oris muscles following transcranial magnetic stimulations were recorded with surface and needle electrodes. MEPs in masseter muscles (latency 6.9 +/- 0.71 ms, mean +/- SD) due to activation of controlateral cortico-nuclear connections were evoked by magnetic stimulations at 4 cm laterally to the vertex on the biauricular line. These MEPs were followed bilaterally by a silent period lasting about 20 ms and, less constantly, by a later silent period lasting up to 80 ms. The ipsilateral responses to the same stimuli presented shorter latencies and higher amplitudes and they were ascribed to direct stimulation of the trigeminal nerve, probably its intracisternal portion. Ipsilateral masseter "cortical" MEPs could be elicited only by a lower output setting (70% of the maximum output) of the stimulator. Orbicularis oris MEPs were polyphasic and dispersed with latencies ranging from 7 to 11 ms. In patients with hemispheric or capsular ischemic lesions "cortical" MEPs were absent when stimulating the affected hemisphere and present when stimulating the unaffected one. We suggest that the direct corticomotoneuronal projections for the masseter are mainly crossed.
Adult↗
Unilateral enlargement of the masseter muscle.
Benign hypertrophy of the masseter muscle is a relatively uncommon condition which may occur unilaterally or bilaterally. The etiology of the ailment is unclear in the majority of cases, and the histopathological features are usually those of normal muscle. A case of unilateral masseter muscle enlargement is described in a 19-year-old Arab male. The histopathological findings were compatible with a mild myopathic disorder. The characteristics, differential diagnosis, etiology, treatment and histopathological features of masserteric hypertrophy are discussed.
Adult↗
Effect on prostaglandin E2 and leukotriene B4 levels by local administration of glucocorticoid in human masseter muscle myalgia.
Our aim was to determine whether masseter muscle (M) and plasma (P) levels of prostaglandin E2 (PGE2) or leukotriene B4 (LTB4) are influenced by local glucocorticoid administration and whether such changes would be associated with corresponding changes in local pain or hyperalgesia. Eighteen patients with fibromyalgia and 15 with local masseter myalgia were examined immediately before and 2 weeks after intramuscular administration of glucocorticoid with regard to masseter muscle resting pain and tenderness to palpation, pressure pain threshold, maximum voluntary mouth opening (MVM), and pain on maximum voluntary mouth opening. The primary criteria for inclusion were presence of pain for a period of at least 3 months and tenderness to digital palpation in the masseter muscle region. At both visits microdialysis samples were obtained from the masseter muscle, and venous blood was collected for analysis of PGE2 and LTB4. Dialysate levels of M-PGE2 did not change significantly after glucocorticoid administration, but reduction of masseter resting pain and increase of MVM were associated with decrease of M-PGE2 in the patients with fibromyalgia. Dialysate levels of M-LTB4 increased in both groups. In the patients with local myalgia the plasma level of LTB4 also increased, and this increase was associated with a decrease of pain and masseter tenderness. In conclusion, this study shows that reduction of masseter level of PGE2 after intramuscular glucocorticoid administration is associated with a decrease of resting pain in patients with fibromyalgia. In addition, the masseter muscle level of LTB4 increases in patients with fibromyalgia and local myalgia.
Adult↗
Histochemical fibre-type profile in the human masseter muscle.
A histochemical characterization of the masseter muscle was performed on biopsy samples of dentate subjects with normal occlusion. There was a continuum of ranges of oxidative and glycolytic capacities of the masseter muscle fibres. Besides the lightly-stained type I and the darkly-stained type II fibres, fibres with intermediate staining reactions for standard ATPase at pH 9.4, IM fibres, were seen in all biopsy samples. IM fibres had some staining characteristics in common with type I, i.e. the reaction for NADH-TR and for ATPase after preincubation at pH 4.6 and 4.2. Like type II fibres they showed strong reaction for menadione-linked alpha-glycerophosphate dehydrogenase and for phosphorylase. The ATPase reaction after preincubation at pH 4.6 did not generally reveal subtypes of type II. It is concluded that the masseter muscle in normal human subjects has a very special fibre composition, with ATPase-IM fibres being a part of the normal fibre population.
Adenosine Triphosphatases↗
Electromyographic heterogeneity in the human temporalis and masseter muscles during static biting, open/close excursions, and chewing.
The human temporalis and masseter muscles are not activated homogeneously during static bite force tasks. In this study, we studied the possible existence of regional differences in these muscles under dynamic conditions. Electromyographic (EMG) activity was recorded by means of bipolar fine-wire electrodes. Six electrodes were inserted into the temporalis muscle and three into the masseter muscle. Recordings were made during maximal effort intercuspal and incisal static clenches, open/close excursions from both the intercuspal and incisal positions, and unilateral gum and licorice chewing on right and left sides. The EMG peak amplitudes and the peak occurrences were compared. During the static clenches and the open/close excursions, no differences could be demonstrated between the regions of the temporalis muscle. However, during the chewing tasks, the anterior and posterior regions behaved differently. Throughout almost all tasks, both superficial and deep parts could be distinguished in the masseter muscle. A further division of the deep masseter was task-dependent. In both the temporalis and masseter muscles, maximal activity (100%) was reached during intercuspal clenches. The average activity declined to 35% of the maximal activity in the temporalis muscle, to 47% in the deep, and to 86% in the superficial masseter during incisal clenches. During all chewing tasks, the EMG peak activity of the anterior temporalis and the superficial masseter muscles was higher in the working than in the balancing condition. The general finding was that different regions were preferentially activated, according to task. The detailed regional specialization previously observed during static bite force tasks could not be demonstrated in the present study.
Adult↗
Effects of two different units of botulinum toxin type a evaluated by computed tomography and electromyographic measurements of human masseter muscle.
BACKGROUND: Masseteric hypertrophy is recognized as an asymptomatic enlargement of one or both masseter muscles. Botulinum toxin type A injection into the masseter muscle can be alternatively used as a noninvasive treatment for masseteric hypertrophy. The aim of this study was to evaluate the effects of two different quantities of botulinum toxin type A on the thickness and cross-sectional area and electromyographic changes in the masseter muscle using computed tomography and electromyographic measurement. METHODS: Thirty-two Korean subjects were enrolled in this study. Twenty-five units of botulinum toxin type A was injected bilaterally in the masseter muscle of 16 subjects, and 35 U was injected bilaterally in the remaining 16. The thickness and cross-sectional area of the masseter muscle were measured at three positions before and 12 weeks after injection using computed tomography. The electromyographic changes in the masseter muscle during maximum voluntary clenching were also evaluated before and 2, 4, 12, and 24 weeks after injection. The difference in the results was statistically analyzed. RESULTS: Statistically significant differences before and after injection were observed when the dimensions and electromyographic values of the masseter muscle were evaluated. However, there was no significant difference between the 25-U and 35-U injections of botulinum toxin type A. The least reduction of muscle thickness was found at the site farthest from the injection point. Several mild side effects were reported, all of which were temporary and localized. CONCLUSIONS: Botulinum toxin type A is effective in treating hypertrophy of the masseter muscle, but the dose of the toxin is not associated with its effectiveness within the limits of this study.
Adult↗
The contribution of the deep fibers of the masseter muscle to selected tooth-clenching and chewing tasks.
Anatomically, the human masseter muscle consists of at least two portions (pars superficialis, pars profunda) with distinctly different fiber directions. The purpose of this study was to describe functional behavior in the deep fibers of the masseter muscle and to define any differences in its behavior from that of the superficial fibers. In 20 subjects, EMG activity of the superficial and the deep portions of the masseter muscle was recorded during specific parafunctional (intercuspal and eccentric tooth clenching) and functional (unilateral chewing) tests. Superficial and deep activity was measured with bipolar surface electrodes and intramuscular fine-wire electrodes. Simultaneously, displacement of a lower incisor point was recorded in three dimensions. The data were collected and stored for analysis by a disk-based computer system. The results indicated that changes in the direction of effort, in mandibular position, and in the side used for chewing all influenced activity in both parts of the muscle to different extents. The most distinct separation of activity occurred when intercuspal clenching was directed retrusively; the deep fibers of the masseter muscle response reduced to 47.5% of its maximum value while that of the superficial fibers of the masseter muscle fell to 5.5%. During chewing, activity in the deep fibers of masseter muscle was distributed evenly bilaterally, whereas that in the superficial fibers of the masseter muscle was biased significantly toward the chewing side. Differentiation of activity within the masseter muscle may be relevant to the distribution of regional tenderness in the muscle when it is involved in parafunctional activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗