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PubMed1991

Cortical potentials associated with voluntary biting movement in humans.

We compared the distribution of Bereitschaftspotentials (BPs) on both sides of the scalp preceding jaw biting movements in order to identify the relationship between the cortical regions and the activation of the masseter muscle in 10 healthy subjects. The BPs were recorded from the midline-central, central and temporal areas of the scalp according to the international 10-20 system, preceding self-paced biting on one side. The cortical negative potentials began 1.0 approximately 1.5 s before the EMG onset of the masseter muscle. All of these negative potentials could be considered to be BPs, and the additional negative slope component (NS) occurred 70 approximately 80 ms before the EMG onset of the masseter muscle. The BPs were detected from all the recorded regions of the scalp, while the NS was observed only from the bilateral temporal area. The amplitudes of BPs and NSs were largest in the temporal areas (T3 and T4) that were ipsilateral to the biting. The rates of occurrence of NS at T3 and T4 ipsilateral temporal areas were 80% and 60%, respectively. These results suggest that unilateral biting movements may be controlled mainly from the ipsilateral hemisphere.

Adult↗
PubMed1997

Treating the open bite.

Tongue thrust is involved in nearly all open bites. An open bite can be created by tongue thrust, tongue posture or mandibular posture. Tongue is an unusual muscle in that its contraction allows it to assume many shapes; its influence in the swallow can create an open bite in the area dictated by the contraction, thrust or rest position. Once space has been created between the upper and lower teeth by the tongue it continues to enter the space created, consequently enlarging the space. Skeletal open bites do not occur in patients whose masseter muscles are active during the swallow (an open bite can develop in these individuals due to habit or during orthodontic therapy). In these individuals the masseters fully contract during the swallow. The weaker the masseter muscles, the more likely an open bite will either be present or may develop during orthodontic treatment. Orthodontic movement will always result in occlusal interferences at some point in treatment. Occlusal interferences during orthodontic treatment make it difficult for patients to find a comfortable biting position. At this point they do not fully contract--"squeeze"--the masseters during the swallow to avoid traumatizing the teeth. Once the masseter squeeze is reduced, the tongue must contribute more to the swallow than when the masseters were more actively involved. The tongue becomes the cushion for the dentition during the swallow. The tongue now positions itself between the teeth during the swallow and the open bite during orthodontic treatment is born. Once the open bite occurs it is best to treat it immediately as the open bite thus created will only worsen with time. If the patient was originally a counterclockwise grower (brachycephalic), it is easier to correct. A clockwise grower (dolichocephalic) is hardest to correct, but can be corrected with patience, perseverance, exercise and a properly constructed tongue thrust appliance. While it is true that some skeletal configurations (i.e. clockwise growers, dolichocephalic facial types) lend themselves to the development of an open bite, the skeletal configuration itself seldom produces an open bite. The tongue is the main progenitor of open bites and it is also responsible for perpetuating the open bite. Dolichocephalic facial types lend themselves to open bite development as any orthodontic treatment which either distalizes molars or allows molars to extrude will tend to wedge the mandible and dentition open. (In this type of patient the masseter muscles develop insufficient force on closure to intrude the molars.) Once the bite opens, the tongue now enters the picture in order to complete the swallow. The open bite immediately worsens. The open bite thus created may require several months to correct. In the clockwise growth patient it is imperative that all precautions be taken during treatment to counteract open bite development. It is also imperative that an open bite, once detected, be treated immediately as the longer it persists the more difficult it becomes to treat. If left untreated, it becomes a habit and the more engrained a habit the more effort needed to change it.

Adolescent↗
PubMed2006

Expression of vesicular glutamate transporter 1 immunoreactivity in peripheral and central endings of trigeminal mesencephalic nucleus neurons in the rat.

The major neuronal components of the trigeminal mesencephalic nucleus (Vmes) are primary afferent neurons that convey proprioceptive information from the cranioorofacial regions. In the present study, we examined expression of vesicular glutamate transporters (VGLUTs), VGLUT1 and VGLUT2, in the primary afferent neurons of the Vmes (Vmes neurons) in neonatal and adult rats. VGLUT1 immunoreactivity was detected in the cell bodies of Vmes neurons in neonatal rats younger than 11 days old, but not in older rats. However, in situ hybridization signals for VGLUT1 mRNA were detected in both neonatal and adult rats. No VGLUT2 immunoreactivity was detected in Vmes neurons of neonatal or adult rats. VGLUT1 immunoreactivity was also seen in the peripheral sensory endings on the equatorial regions of intrafusal fibers of muscle spindles in the masseter muscles in both neonatal and adult rats. In adult rats injected with cholera toxin B subunit (CTb) into the masseter nerve, central axon terminals of Vmes neurons were identified on masseter motoneurons within the trigeminal motor nucleus (Vm) by transganglionically and retrogradely transported CTb. VGLUT1-immunopositive axon terminals in close apposition to CTb-labeled Vm motoneurons were also detected by dual-immunofluorescence histochemistry for VGLUT1/CTb. Electron microscopy after dual immunolabeling for VGLUT1/CTb by the VGLUT1/immunoperoxidase and CTb/immunogold-silver methods further revealed synaptic contact of VGLUT1- and CTb-immunopositive axon terminals upon CTb-labeled neuronal profiles within the Vm. These data indicate that VGLUT1 is expressed in both the central axon terminals and the peripheral sensory endings of Vmes neurons, although no VGLUT1 immunoreactivity was detectable in the cell bodies of Vmes neurons in adult rats.

Aging↗
PubMed1992

Evidence that the masticatory muscles receive a direct innervation from cell group k in the rabbit.

These experiments have shown that a group of neurons lateral to the trigeminal motor nucleus innervates the muscles of mastication. The work began to describe the location of digastric last-order interneurons, using the technique of transneuronal labeling with wheatgerm agglutinin-conjugated horseradish peroxide injected into the left digastric muscle of rabbits under general anaesthesia. Four to eight days later, the animals were killed with an overdose of anaesthetic and perfused. Coronal sections of the frozen brainstem were cut at 20 microns thickness and processed for peroxidase activity. Motoneurons in the ventral and caudal divisions of the trigeminal motor nucleus were labeled in all animals as expected. An additional population of neurons located ventrolaterally to the motor nucleus in cell group k were also found to be labeled if the survival time was five days or more. In an attempt to determine whether cell group k neurons were labeled transynaptically, two series of control experiments were carried out. In the first, crystals of fluorescein- and rhodamine-conjugated dextran amines and horseradish peroxidase were applied directly to central ends of cut digastric nerves. In the second, central ends of cut digastric nerves were enclosed in cuffs containing 40-60% horseradish peroxidase solutions. Again, neurons in both the trigeminal motor nucleus and cell group k were labeled suggesting that neurons within cell group k project to the digastric muscle. Similar experiments using dextran amines and wheatgerm peroxidase were carried out on the masseter muscle. Motoneurons in the dorsomedial and rostral half of the trigeminal motor nucleus, as well as primary afferent cell bodies in the mesencephalic nucleus of the trigeminal nerve, were labeled in all experiments. In addition, a population of neurons in cell group k, dorsal to those associated with the digastric muscle, were found to contain each one of the reaction products. Since it is thought that only the wheatgerm agglutinin-conjugated horseradish peroxidase transferred from one neuron to another, we conclude that cell group k neurons provide an additional innervation to the digastric and masseter muscles.

Animals↗
PubMed2003

Excitatory effects of hypocretin-1 (orexin-A) in the trigeminal motor nucleus are reversed by NMDA antagonism.

Hypocretin-1 and -2 (Hcrt-1 and -2, also called orexin-A and -B) are newly identified neuropeptides synthesized by hypothalamic neurons. Defects in the Hcrt system underlie the sleep disorder narcolepsy, which is characterized by sleep fragmentation and the involuntary loss of muscle tone called cataplexy. Hcrt neurons project to multiple brain regions including cranial and spinal motor nuclei. In vitro studies suggest that Hcrt application can modulate presynaptic glutamate release. Together these observations suggest that Hcrt can affect motor output and that glutamatergic processes may be involved. We addressed these issues in decerebrate cats by applying Hcrt-1 and -2 into the trigeminal motor nucleus to determine whether these ligands alter masseter muscle activity and by pretreating the trigeminal motor nucleus with a N-methyl-d-aspartate (NMDA) antagonist to determine if glutamatergic pathways are involved in the transduction of the Hcrt signal. We found that Hcrt-1 and -2 microinjections into the trigeminal motor nucleus increased ipsilateral masseter muscle tone in a dose-dependent manner. We also found that Hcrt application into the hypoglossal motor nucleus increases genioglossus muscle activity. Pretreatment with a NMDA antagonist (d-(-)-2-amino-phosphonovaleric acid) abolished the excitatory response of the masseter muscle to Hcrt-1 application; however, pretreatment with methysergide, a serotonin antagonist had no effect. These studies are the first to demonstrate that Hcrt causes the excitation of motoneurons and that functional NMDA receptors are required for this response. We suggest that Hcrt regulates motor control processes and that this regulation is mediated by glutamate release in the trigeminal motor nucleus.

2-Amino-5-phosphonovalerate↗
PubMed2006

Intramasseteric schwannoma in a child.

Schwannoma arising in muscle is rare. We treated a very unusual case of schwannoma originating in the masseter muscle in a 12-year-old boy, who presented with a 1-year history of a painless left cheek mass. CT and MRI revealed that the mass existed in the masseter muscle. It was extirpated under general anesthesia without postoperative sequelae. The whitish mass was solid and encapsulated, and pathologic examination confirmed the diagnosis of schwannoma consisting of Antoni A and Antoni B areas. Definitive diagnosis of schwannoma before surgery is usually difficult; hence, histological examination during or after surgery is, in most cases, decisive. However, schwannoma should be considered in the preoperative differential diagnosis of intramuscular tumor, despite its rare occurrence, since postoperative neurological sequelae may occur.

Child↗
PubMedDate not supplied

Changes in neck electromyography associated with meningeal noxious stimulation.

OBJECTIVE: To determine if the activity of jaw and neck muscles in a rat model is influenced by the application of small-fiber irritant mustard oil to meningeal/dural vascular tissues. DESIGN: Controlled animal experiment. SETTING: University neurophysiology laboratory. INTERVENTIONS: Applications of mineral oil (vehicle control) and mustard oil to exposed meningeal/dural vascular tissues. MAIN OUTCOME MEASURE: Electromygraphic (EMG) recordings from deep suboccipital muscles, bilaterally, and the left trapezius and left masseter muscles. RESULTS: Mineral oil evoked no EMG responses in any muscles. The incidences of mustard oil-evoked EMG increases were 100%, 100%, 89% and 78% for left deep neck, right deep neck, left trapezium and left masseter muscles, respectively. The durations of EMG responses were (mean +/- SD) 19.2 +/- 6.6 min, 17.3 +/- 7.5 min, 14.5 +/- 6.8 min and 12.7 +/- 8.5 min, respectively. CONCLUSIONS: These results document that meningeal/dural vascular irritation leads to sustained and reversible activation of neck and jaw muscles that may be related to the clinical occurrence of muscular tension and pain associated with certain types of headaches, particularly migraine.

Animals↗
PubMed2001

Specificity and reversibility of the training effects on the concentration of Na+,K+-Atpase in foal skeletal muscle.

The purpose of the present study was to determine whether training and detraining affect the Na+,K+-ATPase concentration in horse skeletal muscles, and whether these effects are specific for the muscles involved in the training programme. Twenty-four Dutch Warmblood foals age 7 days were assigned randomly to 3 groups: Box (box-rest without training), Training (box-rest with training: short-sprint) and Pasture (pasture without training). Exercise regimens were carried out for 5 months and were followed by 6 months of detraining. Five of the foals in each group were subjected to euthanasia at age 5 months and the remaining foals at 11 months. Muscle samples were collected from the deep part of the gluteus medius, semitendinosus and masseter muscles. The Na+,K+-ATPase concentration was quantified by [3H]ouabain binding. In the Training group, the concentration of Na+,K+-ATPase in gluteus medius and semitendinosus muscle, but not in masseter muscle, showed a relative increase of 20% (P<0.05) as compared to Box foals. After detraining for the subsequent 6 months, the concentration of Na+,K+-ATPase in semitendinosus muscle remained the same, while that in gluteus medius muscle was reduced by 10%. It is concluded that: 1) short-sprint training for 5 months induced an increase of the Na+,K+-ATPase concentration in gluteus medius and semitendinosus muscles of the foal. Interestingly, this effect persisted during the 6 months of the detraining period. Whether the higher Na+,K+-ATPase concentration due to training of young foals leads to a better athletic performance when they become mature still needs to be established; 2) the factors that initiate an increase in Na+,K+-ATPase concentration following training are likely to be located in the muscle itself and 3) the training effect may last for several months after returning to normal activity, especially in muscles containing a high percentage of fast-twitch fibres.

Animals↗
PubMed1987

[The influence of blood supply on craniofacial growth. 4. Reactions of the jaw musculature].

The dry weight of the chewing muscles differ distinctly between male and female. In rats aged 8 to 12 months the dry weight of the chewing muscles after ligature of the carotid artery was lower on the side of the ligature. Necrotic fibres were occasionally found in the masseter muscle on the ligature side. Morphometric investigation of the masseter muscle fibres revealed no significant differences between the 2 sides in the operated rats. Since the rats were relatively young when the commune carotid artery was ligatured unilaterally, the consequences of the initially reduced blood supply to the chewing muscles on the right side could be compensated for rather well, mainly by the enlargement of previously existing anastomoses. Our quantitative and histological studies nevertheless show that muscular dysbalance of the masticatory apparatus was severe.

Animals↗
PubMed1989

Sensory components facilitating jaw-closing muscle activities in the rabbit.

The role of oral and facial sensory receptors in the control of masticatory muscle activities was assessed from the effect of acute deafferentiation on cortically induced rhythmic jaw movements (CRJMs) in anesthetized rabbits. When a thin polyurethane-foam strip (1.5, 2.5 or 3.5 mm thick) was placed between opposing molars during CRJMs, masseteric activities were facilitated in association with an increase in the medial excursion of the mandible during the power phase. The effects varied with the pattern of CRJMs, and the rate of facilitation was greater for small circular movements than for the crescent-shaped movements. Furthermore, the response of the masseter muscle was greater in the anterior half of the muscle, where muscle spindles are most dense, than in its posterior half. It was also demonstrated that the response increased with an increase in the thickness of the test strip. In contrast, the activities of the jaw-opening muscle were not affected significantly. The duration of masseteric bursts increased during application of the test strip and the chewing rhythm tended to slow down. However, the latter effect was not significant. After locally anesthetizing the maxillary and inferior alveolar nerves, the facilitative responses of the masseter muscle to the test strip was greatly reduced but not completely abolished. Lesioning of the mesencephalic trigeminal nucleus (Mes V) where the primary ganglion cells of muscle spindle afferents from jaw-closing muscles and some periodontal afferents are located, also reduced the facilitative effects. Similar results were obtained in the animals with the kainic acid injections into the Mes V 1 week before electrical lesioning of this nucleus. In these animals the effects of electrical lesioning of the Mes V could be attributed to the loss of muscle receptor afferents since the neurons in the vicinity of the Mes V were destroyed and replaced by glial cells, whereas the Mes V neurons are resistant to kainic acid. When electrical lesioning of the Mes V and sectioning of the maxillary and inferior alveolar nerves were combined in animals with a kainic acid injection into the Mes V, the response of the masseter muscle to application of the strip was almost completely abolished. From these findings, we conclude that both periodontal receptors and muscle spindles are primarily responsible for the facilitation of jaw-closing muscle activities.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2002

Gnawing behavior of a mouse in a narrow cylinder: a simple system for the study of muscle activity, fatigue, and stress.

When a mouse is put into a cylinder too narrow for it to turn (its front end being blocked with a thin plastic strip), the mouse gnaws away the plastic to escape. Hence, the weight reduction in the plastic can be used as an index of 'gnawing activity (GA).' GA was high at first, but decreased with time. Training augmented GA, but not the activity of the histamine-forming enzyme (histidine decarboxylase [HDC]: a proposed marker of muscle fatigue) in the masseter muscle. In trained mice, GA was higher at night than in the daytime, and was decreased by starvation. In mice prevented from reaching the strip, the elevation of serum cortisol was greater than that seen in mice able to gnaw at it. As such gnawing is a form of voluntary behavior, these results suggest that our experimental system may be useful for (i) the quantitative study of voluntary muscle activity associated with physical or mental fatigue or motivation, and (ii) the study of an animal's response to stress when it has, or alternatively does not have, an apparent way of escape.

Animals↗
PubMed2004

Blockade of peripheral 5HT3 receptor attenuates the formalin-induced nocifensive behavior in persistent temporomandibular joint inflammation of rat.

The role of peripheral 5HT3 receptors in the orofacial nocifensive behavior induced by the injection of formalin into masseter muscle was evaluated. The behavioral activities evoked by the formalin injection exhibited a biphasic response in the rats with or without temporomandibular joint (TMJ) inflammation (CFA group or non-CFA group). The orofacial nocifensive behavioral activity was enhanced after TMJ inflammation. Systemic administration of tropisetron, 5HT3 receptor antagonist, reduced the nocifensive behavioral activities in the late phase of orofacial formalin test in CFA group, but not in non-CFA group. Local administration of tropisetron into the masseter muscle in CFA group, but not in non-CFA group also attenuated the behavioral activities in the late phase. Unexpectedly, low dose of local tropisetron reduced the nocifensive behavioral activities in the early phase of orofacial formalin test in CFA group. These data suggest that induction of TMJ inflammation causes the elevation of the orofacial nocifensive behavioral activities evoked by formalin injection into masseter muscle, and that peripheral 5HT3 receptors may play a critical role in nociception and the transmission of orofacial pain.

Animals↗
PubMed1999

Jaw reflexes evoked by mechanical stimulation of teeth in humans.

Jaw reflexes evoked by mechanical stimulation of teeth in humans. The reflex response of jaw muscles to mechanical stimulation of an upper incisor tooth was investigated using the surface electromyogram (SEMG) of the masseter muscle and the bite force. With a slowly rising stimulus, the reflex response obtained on the masseter SEMG showed three different patterns of reflex responses; sole excitation, sole inhibition, and inhibition followed by excitation. Simultaneously recorded bite force, however, exhibited mainly one reflex response pattern, a decrease followed by an increase in the net closing force. A rapidly rising stimulus also induced several different patterns of reflex responses in the masseter SEMG. When the simultaneously recorded bite force was analyzed, however, there was only one reflex response pattern, a decrease in the net closing force. Therefore, the reflex change in the masseter muscle is not a good representative of the net reflex response of all jaw muscles to mechanical tooth stimulation. The net response is best expressed by the averaged bite force. The averaged bite force records showed that when the stimulus force was developing rapidly, the periodontal reflex could reduce the bite force and hence protect the teeth and supporting tissues from damaging forces. It also can increase the bite force; this might help keep food between the teeth if the change in force rate is slow, especially when the initial bite force is low.

Adult↗
PubMed1991

In vivo strain in cranial sutures: the zygomatic arch.

Although cranial sutures presumably play a role in absorbing and/or transmitting loads applied to the skull, loading patterns on facial sutures are poorly understood. The zygomatic arch provides a comparatively isolated mechanical part of the skull containing a single suture, the zygomatico-squamosal. In pigs the zygomatico-squamosal suture has a short vertical segment located within the postorbital process and a longer horizontal segment which extends posteriorly. In anesthetized pigs single-element high-elongation strain gages were bonded over both segments of the suture. Strain was recorded during stimulation of the masseter muscles and while the lightly anesthetized animals masticated food pellets. The predominant strain patterns differed in the two segments of the suture. During mastication compressive strains predominated in the vertical segment, but tensile strains predominated in the horizontal segment. The same patterns were also produced by stimulation of the ipsilateral masseter muscle. Contraction of the contralateral masseter reversed the strain pattern, but strain levels were low and during mastication such reversals occurred only transiently. The two segments of the suture have contrasting morphologies. The vertical segment has broad, interdigitating contacts with fibers arranged in a compression-resisting orientation. The horizontal segment has a simple tongue and groove structure with fibers arranged to resist tension. Thus, the structure of the suture reflects the predominant strain pattern.

Animals↗
PubMed1999

The immediate effect of hard and soft splints on the EMG activity of the masseter and temporalis muscles.

The aim of this study was to compare the effects of hard and soft splints on the activity of the anterior temporalis and masseter muscles. Surface EMG recordings were made from these muscles during clenching at 10% of maximum, 50% of maximum and at maximum clench, both before and after insertion of a hard splint. This sequence was then repeated with a soft splint. The relative level of activity in the anterior temporalis and masseter muscles at all three activity levels was quantified by means of an Activity Index, which provides a measure of the balance of activity in the masseter relative to the activity in the anterior temporalis muscle. It was found that hard splints led to a decrease in EMG activity in relation to activity with no splint in both muscles at maximum clench and particularly the anterior temporalis. Soft splints produced a slight increase in activity of both muscles, but particularly the masseter muscle. The Activity Index indicated a shift in the balance of activity away from the anterior temporalis muscles with both splints, particularly at 10% of the maximum clenching level. It is possible that the decrease in activity of the temporalis muscles relative to the masseter muscles may be a factor in the therapeutic effect of both a hard and a soft splint, although the decrease is clearly greater with the hard splint.

Acrylic Resins↗
PubMed1991

Masseter inhibitory reflex in movement disorders. Huntington's chorea, Parkinson's disease, dystonia, and unilateral masticatory spasm.

Evoked by electrical stimulation of the mental nerve, the masseter inhibitory reflex consists of an early and a late silent period (SP1 and SP2), which interrupt the voluntary electromyographic (EMG) activity in the masseter muscle. We recorded the masseter inhibitory reflex and measured its latency, depth of suppression, duration and recovery cycle to paired stimuli, in patients with Huntington's chorea. Parkinson's disease, dystonia, or unilateral masticatory spasm. In patients with Huntington's chorea the reflex data and recovery cycle were normal. In patients with Parkinson's disease or dystonia, although the reflex data were normal, SP2 recovered far more rapidly than it did in control subjects. This is possibly due to hypoactivity of an inhibitory control of the polysynaptic chain of ponto-medullary interneurons that mediate SP2. In patients with unilateral masticatory spasm, both SP1 and SP2 were absent. Suppression is probably absent because this involuntary movement originates at a point along the peripheral course of the nerve.

Adolescent↗
PubMed1985

Distribution of stresses in the human skull.

A three-dimensional photoelastic model was reproduced from a human skull. The insertions of the superficial and deep portions of the masseter muscle, the temporalis muscle, the medial pterygoid muscle and the temporalis fascia were simulated with leather bonded to the appropriate areas. The following loading conditions were employed: (i) all three muscles were bilaterally loaded without occlusal loads; (ii) all three muscles were bilaterally loaded while occlusal loads were simultaneously applied on the maxillary teeth. The stress freezing technique was used to lock the resulting stress patterns into the model skull. The stress trajectories were observed and photographed in a circular polariscope. The mandibular closing muscles and the occlusal loads produced stresses which progressed through the maxilla, following a nasal, a zygomatic and a pterygoid route, while stress concentrations were seen in the frontonasal, zygomaticomaxillary and the pterygopalatine sutures. In the malar bone area the stresses were seen to branch superiorly to the frontozygomatic suture and posteriorly along the zygomatic arch to the zygomaticotemporal suture and the temporal bone. Generally, the stresses were concentrated in those areas of the skull where architectural reinforcement had been demonstrated by other methods.

Bite Force↗
PubMed1986

Utility of the group coefficient of variation in predicting speech-motor equivalence in normal and articulatory disordered speakers.

Coefficients of variation of EMG signals from the orbicularis oris superior, orbicularis oris inferior, and masseter muscles of normal 4- and 8-yr.-olds and adults and of articulatory disordered 8-yr.-olds suggests that development of speech motor equivalence is individualized, muscle-dependent, and affects all children. Age-related differences were noted. Group data did not predict individual values.

Age Factors↗