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At least 19 recordsLinked to original sources
PubMed1989

[Electromyographic (EMG) electrode impedance and EMG activity from anterior temporal muscle and masseter muscle].

The value and change with time of the impedance of surface EMG electrodes and the effects of their difference between the bipolar electrodes on the electromyographic activity from the anterior temporal muscle and the masseter muscle in six adult male subjects with normal occlusion were studied. The results were as follows: 1. In the anterior temporal muscle, if the impedance of the electrode was under 20 k omega it was stable from just after the electrode disc was applied to the skin. In the masseter muscle, if the impedance was under 30 k omega it became stable within two minutes after the electrode was applied. 2. The difference of impedance between the bipolar EMG electrodes did not correlate with EMG activity.

Adult↗
PubMed1990

An animal model for human masseter muscle: histochemical characterization of mouse, rat, rabbit, cat, dog, pig, and cow masseter muscle.

The masseter muscle of several animal species was investigated by use of a histochemical method for the demonstration of acid-stable and alkali-stable myosin adenosine triphosphatase (ATPase). The following subdivisions of fiber types were used: Type I fibers show weak ATPase activity at pH 9.4, type IM fibers react moderately, and type II fibers react strongly. Rat and mouse masseter muscles contained type II fibers only, as did some rabbit masseter muscles, whereas other rabbit masseter muscles possessed equal amounts of type I and II fibers. Cat and dog masseter muscles possessed both type II and I fibers, with type II predominating. Cow masseter muscle consisted mainly of type I fibers, although some cow masseter muscles contained a very small number of type II fibers. Pig masseter muscle had both type I, II, and IM fibers. One of the characteristics of human masseter muscle is type IM fibers, which are rarely seen in muscles other than the masticatory muscles. Therefore, pig masseter muscle might be a suitable animal model for experimental studies, such as an investigation of the distribution and diameter of fiber types in the masticatory muscles before and after orthognathic surgery.

Adenosine Triphosphatases↗
PubMed1989

Prolonged degeneration of muscle spindles in the masseter muscle after treatment of developing mice with the local anesthetic lidocaine hydrochloride.

The effect of lidocaine-HCl on muscle spindles in the masseter muscle of developing mice was investigated. Repeated injections of mice with anesthetic in the short term decreased the diameters of primary endings, intrafusal muscle fibers and outer capsules in the equatorial regions of muscle spindles, and caused a drop in the succinic dehydrogenase activity in intrafusal muscle fibers of the muscle spindles. In addition, the diameters did not recover to the control value even after about 10 weeks following cessation of anesthetic treatment. Thus, the present results suggest that repeated use of lidocaine-HCl in developing animals may cause dysfunction of the skeletal muscles.

Animals↗
PubMed1992

Fine structure of nerve processes containing basic fibroblast growth factor in muscle spindles of the rat masseter muscle.

An antiserum against basic fibroblast growth factor (bFGF) was characterized by immunoblot analysis and used to investigate the fine structure of bFGF-containing processes in muscle spindles of the rat masseter muscle. The bFGF antiserum recognized purified bFGF and bFGF-like materials with the same molecular weight as bFGF in crude homogenate of the brainstem from which bFGF fibers in the masseter muscle spindles presumably originate. Immunoelectron micrographs demonstrated that both proprioceptive and motor nerve endings in contact with intrafusal fibers contain bFGF. These findings suggest that bFGF of central (possibly trigeminal mesencephalic and motor nucleus) origin is transported into the muscle spindles subserving mechanoreception.

Animals↗
PubMed1989

The lamination of the masseter muscle in the Japanese serow (Capricornis crispus).

The lamination of the masseter muscle in 21 Japanese serows of different sexes and ages was studied by the method of Yoshikawa et al. who proposed a lamination theory for this muscle. The masseter muscle in the Japanese serow was found to be composed of I) the proper masseter muscle which included 1) the first superficial, 2) the second superficial, 3) the intermediate and 4) the deep masseter muscles, in which the deep masseter muscle could be subdivided into a pars anterior and pars posterior and II) the improper masseter muscle which included 5) the maxillomandibular and 6) the zygomaticomandibular muscles, in which the maxillomandibular muscle was further divided into first and second layers. These findings indicate that the lamination of the masseter muscle in the Japanese serow is the same as that in the goat and sheep.

Animals↗
PubMed1989

Long-term observations of the masseter muscle following single or repeated injections of lidocaine hydrochloride into developing mice.

Effects of lidocaine-HCl on extrafusal muscle fibers in the masseter muscle of developing mice were studied histologically and morphometrically. In the affected region, many extrafusal muscle fibers were circular and smaller in diameter than unaffected extrafusal muscle fibers, and the SDH activity of the affected fibers was very irregular. In lidocaine-HCl injected groups, the ratios of extrafusal muscle fibers with central nuclei to total extrafusal muscle fibers were higher than those in the saline solution-injected groups. The diameters of extrafusal muscle fibers in the masseter muscle treated with lidocaine-HCl were smaller than those in the saline solution-injected groups. These changes in the muscle with lidocaine-HCl continued for 45 days after a single injection. Five injections of lidocaine-HCl into developing mice caused long-term degeneration of the masseter muscle. Thus, the present study suggests that a local anesthetic agent caused degeneration of immature muscle fibers of the masseter muscle in developing mice and may result in long-term decrease of masticatory capacity. Therefore, lidocaine-HCl may inhibit the synchronized development of masticatory organs in developing animals.

Animals↗
PubMed1991

Measurement of muscle fiber conduction velocity in the human masseter muscle using the surface EMG cross-correlation technique.

During sustained isometric contraction of the jaw muscles, the surface electromyography (EMG) power spectrum compresses into lower frequencies. This compression has been mainly attributed to the change of the conduction velocity of the action potentials along the muscle fibers. In this study, the muscle fiber conduction velocity of the masseter muscle was measured by using the surface electrode array and the cross-correlation technique. The conduction velocity of the masseter muscle varied from 6.83 to 18.01 m/s among the eight subjects, and slightly increased with the contraction level.

Adult↗
PubMed1991

[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↗
PubMed1991

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↗
PubMed1989

[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↗
PubMed1990

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↗
PubMed1989

[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↗
PubMed1991

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↗
PubMed1979

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↗
PubMed1989

Experimental studies on masseter muscle grafts in rats: comparison of donor muscles.

Experimental studies were performed in rats to explore the feasibility of using limb muscles to replace masticatory masseter muscles. The results showed that if several small fusiform muscles such as the extensor digitorum longus (EDL), soleus (SOL) and plantaris (PLT) were used for the grafting, the graft regenerated and matured fully in the masseter bed, although the weights were lower than those of contralateral control masseter muscles. If a multipennate muscle such as the gastrocnemius was used for the grafting, the graft also regenerated but later degenerated due to the lack of innervation. This is probably due to the excessive amount of connective tissue in the multipennate muscle. The connective tissue proliferates faster than the regeneration of muscle fibres and, thus, renders the innervation of muscle fibres difficult. Other factors pertinent to the possible clinical application of muscle transplantation in oral region are discussed.

Animals↗
PubMed1991

[Anatomo-topographic characteristics of the masseter muscle].

The musculus masseter, ensuring movements of the mandible, displace the osseous pieces at its fracture up/down in the lateral and medial sides. Morphometrical investigation of the musculi depressores++ mandibulae has been performed. As a whole 33 corpses (29-78 years of age) of normosthenic++ complexion have been studied. The measurements have been performed by means of a special compasses and a ruler with an approximation to 1 mm and 1 degree. The length of the digastric muscle belly is 55.3 +/- 1.1 mm. The length of the geniohyoid muscle is 44.5 +/- 0.9 mm. The distance between the centers, where the digastric muscle are fixed on the hypoglossal bone is 46.1 +/- 1.1 mm, and on the mandible--25 +/- 9 mm. The width of fixation of the musculus mylohyoideus on the mandible is 52.6 +/- 1.2 mm. The angles between the masseter muscles, the mandibular body and the occlusive plane have also been determined.

Adult↗
PubMed1992

Observation of proportionality of myoelectrical activity of anterior temporalis to masseter muscle during clenching at varied jaw positions.

Twelve healthy subjects with an intact permanent dentition and normal occlusion were selected for sampling of myoelectrical activity of their left and right anterior temporal and masseter muscles during habitual clenching level in varied positions. The proportionality of normalized myoelectrical potentials of anterior temporal muscle to masseter muscle at ICP and RCP was greater than one, while the proportionality at PP was less than one. In the lateral position, the proportionality on the working side was approximately equal to that at RCP, while the proportionality on the non-working side was similar to that at PP. These results suggest that temporal muscle contraction can bring the mandible upward and backward whilst the masseter muscle can elevate the mandible upward and forward.

Action Potentials↗