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PubMed1988

Computed tomographic evaluation of the density of the temporomandibular joint meniscus.

Pathologic alteration of the articular disk, including moderate calcification within the meniscus proper, has been reported to occur in many cases of TMJ dysfunction with chronic anterior meniscal displacement. The purpose of this investigation was to measure, by means of direct sagittal computed tomographic scanning technology, the density (x-ray attenuation) of the meniscus. Fifty-two joints, shown to have meniscus displacement with or without reduction (MD/MDR), and 24 symptomatic joints with normal tomograms were evaluated with the use of a GE 8800 CT scanner. Mean attenuation values were extrapolated with the use of a symmetrical (1 to 9 pixels) region-of-interest (ROI) cursor. Density gradients of the masseter muscle, lateral pterygoid fat pad, and lateral pterygoid muscle were also obtained. The results of this study showed that the mean meniscal density values were 116.7 +/- 4.2 Hounsfield units (HU) for MD subjects, 111.3 +/- 4.6 HU for MDR subjects, and 82.4 +/- 2.9 HU for subjects with symptoms. The MD and MDR density group means were significantly different (p less than 0.001) from the normal group means. A relative comparison of the meniscus density with that of the lateral pterygoid muscle, its fat pad, and the masseter muscle showed a consistent mean difference when the paired t test was used. Meniscal displacement was found to be associated with an increase in density gradient, which suggests histologic alteration.

Adult↗
PubMed1981

[Effect of head posture on muscle tonus of the masticatory muscles].

The integrated electromyographic study allows to determine action of the variation amplitudes of tonic activity of the masseter muscles, the anterior temporalis muscles and the trapezius muscles induced by angular cephalic displacements of 10 degrees in the three space planes, in sitting position (P.A) and upright position (P.D.). The direction of the variations can be simultaneously positive or negative according to the vertical reference position (P.R.) in the different muscles studied. The masseter muscles showed the largest variations of the P.A. to the P.D. Twenty per cent of the subjects can be classified in a hypertonic category.

Adult↗
PubMed1981

Distribution of stress patterns in the human zygomatic arch and bone.

A three-dimensional photoelastic model was reproduced from a human skull. The insertions of the superficial and deep portions of the masseter muscle and the temporalis fascia were simulated with leather bonded to the appropriate areas. The following loading conditions were employed: (1) bilateral loading of the masseter muscle; and (2) bilateral loading of the masseter muscle together with a bilateral occlusal load. Ther 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 results suggest that the major stress trajectories to the zygomatic bone and arch follow an alveolo-maxillary-zygomatic-temporal direction. Stresses were highly concentrated in the zygomatic process of the temporal bone. Generally, the stresses were concentrated in those areas of the bone where architectural reinforcement had been demonstrated by other methods.

Dental Occlusion↗
PubMed1987

[The influence of the masticatory muscles on craniofacial growth. A microsurgical study in the rat].

Possible influence of masticatory muscles on facial growth was investigated in the rat by the formation of several experimental groups: excision of right masseter muscle of right temporal muscle, of both masseter muscles, of both temporal muscles and of both masseter and temporal muscles, section of inferior maxillary nerve and masseter transplantation. Results demonstrated that overall masticatory muscles provided equilibrium of masticatory function, any rupture of this equilibrium producing effects on mandibular growth and that of the facial mass.

Aging↗
PubMed1981

An electromyographic and cephalometric study on facial pains and facial morphology in children.

Twelve children, five girls and seven boys with a mean age of 12 years, exercised maximal voluntary tooth clenching until intolerable pains and total subjective exhaustion of at least the right masseter muscle forced the children to stop the isometric muscle exercise; that is, the pain tolerance, or the isometric endurance time, of at least the right masseter muscle was determined in seconds, and it amounted to an average of 100 s. Concomitantly, the electrical activity in the right masseter muscle was recorded by bipolar surface electrodes and integrated, and it showed a significant decrease of 32% during the endurance test, probably as an expression of progressive physiological muscle fatigue. A large ANB angle was associated with relatively little decline of the contractile activity and a trend not to endure pains, possibly because isometric tension was generated predominantly by muscle fibres with a high anaerobic capacity.

Cephalometry↗
PubMed1982

The 'late' reflex responses to muscle stretch: the 'resonance hypothesis' versus the 'long-loop hypothesis'.

1. Experiments were performed to check the validity of previous claims concerning the ;long-loop' aetiology of ;late' reflex electromyogram (e.m.g.) responses to muscle stretch in man. The primary aim was to investigate whether observations previously presented in favour of the ;long-loop hypothesis' are explicable also in terms of the ;resonance hypothesis', according to which the ;late' reflex components represent spinal, short-latency responses to intramuscular oscillations initiated by the impact.2. The contracting wrist flexors of healthy subjects were exposed to trains of recurrent 25-50 Hz stretch stimuli (wrist torque pulses). Each of the initial two or three pulses in the train was followed by e.m.g. peaks with a latency of 20-25 msec. The e.m.g. peaks driven in this way had the following characteristics in common with the successive two or three e.m.g. peaks which were induced by single ramp stretches or tendon taps. (a) Changes in stimulus parameters which altered the strength of the initial e.m.g. peak often had an opposite effect on the strength of the succeeding peak(s). Muscle vibration which attenuated the initial peak often enchanced the succeeding one(s). (b) The initial e.m.g. peak was less affected than the succeeding peak(s) by the subjects' attempts to respond with rapid ;resist' or ;let go' reactions.3. Intramuscular oscillations (monitored by a needle accelerometer) and e.m.g. responses evoked by single ramp stretches and/or tendon taps were also studied in the long thumb flexor, the calf muscles and the masseter muscle. In the thumb flexor, the initial accelerometer deflexion was only rarely succeeded by a short latency e.m.g. peak, but the succeeding wave in the needle accelerogram was followed by such a peak, appearing about 40 msec after stimulus application. By contrast, the calf muscles and the jaw elevators exhibited a high amplitude, short-latency e.m.g. response to the first but only rarely to the second intramuscular oscillation wave.4. The interval between initial and second e.m.g. peaks following tendon taps was longer for calf muscles than for wrist flexors and longer for wrist flexors than for jaw elevators. Similar differences were observed with respect to the intervals between the damped intramuscular oscillations initiated by the impacts.5. Without denying the existence of ;long-loop reflexes' it is concluded that the characteristics of the ;late' reflex responses to muscle stretch in man are explicable also in terms of the ;resonance hypothesis'.

Adult↗
PubMed1997

Muscle activity during mandibular movements in normal and mandibular retrognathic subjects.

PURPOSE: The masticatory muscles function as a unit during precise mandibular positioning movements that occur during such activities as speech, singing, or playing musical instruments. This investigation was designed to assess jaw muscle recruitment patterns during controlled mandibular movement in normal subjects and in patients with mandibular retrognathism. PATIENTS AND METHODS: A computer-integrated electromyography (EMG) and movement monitoring (Selspot) system was used to collect data over 7 seconds of a sagittal border movement (Posselt envelope) of the mandible and 4 seconds each of rest position, light tooth contact, and maximum clench. Fine wire bipolar electrodes were placed into the inferior belly of the lateral pterygoid muscles bilaterally and surface electrodes were placed bilaterally over the anterior belly of the temporalis muscles and the masseter muscles. Ten subjects with Class I occlusion, normal cephalometric values, and an absence of temporomandibular joint (TMJ) dysfunction were compared with 12 patients with mandibular retrognathism, Class II malocclusion, and an absence of clinical signs of TMJ internal derangement before and after a bilateral sagittal split and advancement of the mandible. RESULTS: There was a wide variation in standard deviations of EMG activity for the lateral pterygoid muscles in the retrognathic patients compared with normal controls before surgery (P < .05). In light tooth contact, temporalis muscle activity increased after surgery with respect to both control and the presurgical levels (P < .05, P < .005, respectively). In maximum clench, activity in all muscle groups in the retrognathic patients, both before and after surgery, were below that of control subjects (P < .005). The lateral pterygoid muscles showed late recruitment, with low EMG activity levels during the forward movement phase of the envelope, before surgery compared with controls (P < .001). After surgery, the lateral pterygoid muscle showed early recruitment in the forward movement similar to control levels. CONCLUSION: The masticatory muscles function as a unit during mandibular positioning movements. Patients with mandibular retrognathism have different muscle recruitment patterns from those of normal subjects with the mandible at rest and during mandibular movement. After orthognathic surgery, adaptation occurs in the phasic timing of jaw muscle activity.

Adaptation, Physiological↗
PubMed1987

[Functional morphology of the maxillo-mandibular apparatus of the mini-Lewe minipig. 2. Structure of the masticatory muscles of adult animals].

The masseter muscle is the most powerfully developed of the jaw muscles in the miniature pig MINI-LEWE. Its internal skeleton contains 5 Sehnenspiegel. The zygomatico-mandibular muscle acts as a link between the masseter and temporal muscles. The pinnate structure of the temporal muscle results from the internal tendons, which attach to the coronoid process. The medial pterygoid muscle with its 7 Sehnenspiegel has the most complex pinnate structure. The lateral pterygoid muscle has small tendinous slips only in the regions of its origin and attachment.

Animals↗
PubMed2001

Effects of masticatory muscle function and bite-raising on mandibular morphology in the growing rat.

The aim of this series of investigations was to study the effect of masticatory muscle function on the growth pattern and on the internal structure of the mandible during growth. The muscular and dentoskeletal growth adaptation to prolonged bite-raising and the role of the functional state of the masticatory muscles in this adaptation were also to be elucidated. Differences in masticatory muscle function were induced in young rats by altering the consistency of the diet. Bite-raising was produced by the insertion of posterior bite blocks. Morphometric analysis of the internal bone structures of the mandible was performed on microradiographs, and videodensitometric analysis was performed on lateral radiographs and microradiographs. The effect of muscle function and bite-raising on mandibular growth was studied on a series of lateral cephalograms, superimposed on bone markers. Muscle belly, sarcomere and aponeurosis length adaptation to bite-raising was studied in situ with a digital caliper and under a microscope after fluorescent vital staining of the deep masseter muscle. A soft diet altered the pattern of growth of the mandible and reduced bone growth in the angular region. Transversal dimensions and cross-sectional area of the dentoalveolar process were smaller. Bone mass in areas possibly subjected to direct loads or bending forces was smaller. This was due to either less trabecular bone or thinner cortical bone. Only a few sites showed lower bone density. Posterior bite-blocks affected the size of the mandible as well as its growth pattern, and intruded lower molars. The soft diet influenced the effect of bite-blocks and caused less intrusion of upper molars and less inhibition of bone growth at the angular process. The deep masseter muscle adapted to bite-raising by elongation of the aponeurosis, but less in rats on a soft diet. Changes in masticatory muscle function affected the growth of the mandible in both the sagittal and transversal plane. Reduced loads on molars and condyle and smaller bending forces in other regions of the mandible possibly reduced the levels of stimulation of the osteocyte network and osteoblasts, thus inducing less trabecular bone and cortical bone formation in specific areas. In rats fed the soft diet, smaller increase in bone density represented an adaptation process in areas characterised by a lower bone apposition rate. The forces produced by the passive stretching of the masseter muscle affected the skeletal growth pattern and dental eruption. Weaker forces possibly produced by passive stretching of hypofunctional muscles resulted in more eruption of the upper molars and less inhibition of periosteal bone apposition in the angular region. Length adaptation in the masseter muscle through lengthening of the aponeurosis and dentofacial growth adaptation possibly decreased passive forces applied to teeth and skeletal structures, particularly in rats with higher functional demands. This may have caused a gradually decreasing effect of the appliance.

Adaptation, Physiological↗
PubMed1989

Distribution of movement-related cortical potential upon jaw-biting in humans.

We examined the cerebral location of the readiness potential (hereinafter referred to as "RP") upon activation of the masseter muscle by voluntary and unilateral jaw-biting movement. Four normal adults served as subjects. Five scalp electrodes were placed according to the international 10-20 method at CZ, C3, C4, T3 and T4. In addition, in one of the subjects, RPs were recorded by 12 scalp electrodes in order to study changes occurring in the distribution of RPs with time. The maximum amplitude of the RP was located at T4 in the temporal area, which was involved in the biting movement as a negative slow potential occurring 1.4-0.8 s before the beginning of the discharge to the masseter muscle. The maximum amplitude of the RP on the contralateral side was located at T3. This meant that the amplitude of the RP tended to be higher on the same side as the biting movement than on the contralateral side in all subjects. From scalp topography, the maximum amplitude of the RP was shown to be confined to T4, and was especially marked immediately before the beginning of discharge to the masseter muscle. From these results it is thought that in the case of voluntary biting movement, the RP reflects activities of the pyramidal cells in the masticatory area of the cortex, and that strong descending impulses from both sides then reach the masseter muscles.

Action Potentials↗
PubMed1989

Incidence of centrally positioned nuclei in mouse masticatory muscle fibers.

Cross-sections of normal digastric, temporalis and masseter muscles from 7- and 30-week-old mice were studied for centrally positioned nuclei. Such nuclei were inhomogeneously distributed throughout each muscle and varied markedly between specimens. The incidence of centrally positioned nuclei in the digastric muscle (mean +/- SD: 0.029 +/- 0.015, n = 25) was significantly higher (p less than 0.001) than that in the temporalis (mean +/- SD: 0.011 +/- 0.010, n = 25) and masseter muscles (mean +/- SD: 0.005 +/- 0.007, n = 9), but did not differ between the two latter muscles (p = 0.41). Furthermore, the frequency in a given muscle was apparently age-independent. A connection between fiber type and centrally positioned nuclei is suggested.

Animals↗
PubMed1979

Possible role of thiamine in neuromuscular transmission.

Pyrithiamine (50 mg/kg), a thiamine antagonist, decreased the muscle twitches of the rat masseter muscle at stimulation frequencies above 1 Hz 40--80 min after an i.v. injection. The post-tetanic potentiation (PTP) induced by nerve stimulation of the masseter muscle was abolished by pyrithiamine. Administration of thiamine restored the muscle twitches at stimulation frequencies above 1 Hz and the PTP. The muscle twitches elicited by direct muscle stimulation were not affected by pyrithiamine treatment. The abolishment of the PTP was accompanied by a decrease in thiamine and thiamine-diphosphate. The pyruvate level in the blood was unchanged after pyrithiamine treatment. Oxythiamine, on the other hand, had no effect on the PTP but increased the pyruvate level in the blood. Fern extract which contains thiaminase I also abolished the PTP--an effect reversible by the addition of thiamine. The frequency-induced depression of the muscle twitches induced by pyrithiamine was similar to the effect of low doses of d-tubocurarine (8 microgram/kg). The results support the hypothesis that thiamine may play a role in neuromuscular transmission.

Action Potentials↗
PubMed1989

Experimental teeth clenching in man.

The thesis develops an electromyographic (EMG) method to quantify maximum voluntary teeth clenching (MVC), studies the onset and endurance of jaw muscle fatigue and pain from MVC, and explores the prevention of the discomforts through pharmacological and physical means. MVC, or maximum voluntary static work efforts by the elevator muscles of the mandible, was quantified by continuous (integral) functions of variations in both time and recruitment/rate coding of motor units in the masseter muscle. Fatigue was felt in the masseter muscle after about 30 seconds of MVC; differential calculus suggested that the appearance and disappearance of fatigue was associated with primarily recruitment and decruitment of masseteric motor units, respectively. About 60 seconds of MVC elicited a mild pain in the masseter and temporalis muscles; about 120 seconds of MVC induced a moderate pain and complete exhaustion of the isometrically contracting muscles. Although pain releasing maximum static work efforts are stable variables they cannot predict the pain magnitude of brief and prolonged MVC, probably because of modulations (recruitment/decruitment/rate coding) of masseteric motor units. It is suggested that the modulations begin with the onset of fatigue, are practically complete with the onset of pain, and are absent or negligible with an experience of exhaustion. A single oral dose of 1000 mg of ibuprofen did not affect the onset, endurance, and magnitude of pain from MVC. By contrast, 30 minutes of cooling (ice) of the masseter muscle effectively prevented the onset of pain; it also increased the masseteric EMG, credibly because of modulations of myoelectrical signals and, possibly, increased MVC efforts in the absence of pain.

Cryotherapy↗
PubMed1990

[The study of the relationships between the masticatory muscles activity and the craniofacial morphology in mandibular prognathism].

Facial asymmetry is usually manifested in mandibular prognathism. This is probably because of the intervention of masticatory muscles in some way or another. Functional factors of masticatory muscles are also believed to be responsible for the relapse of facial disharmony even after surgical orthodontic treatment. In the present study, cephalometric analysis was made on a total of 43 patients with mandibular prognathism. The functional activity of their masticatory muscles was measured quantitatively by using electromyography. The data thus obtained were analyzed with respect to their bearings on the morphological points of reference given on posteroanterior cephalogram. Our findings are as follows: 1) At the time of maximal clenching with a bite splint, differences in the activity of left and right masseter muscles had a significantly positive correlation with the deviations from the point Menton on the frontal image, and a significantly negative correlation with the angles of the mandibular ramus to the median line on the frontal view. However, no relation was established between the activity of the masseter muscles and that of the temporal muscles on either side. 2) At the time of maximal clenching in central occlusion, differences in the activities of the masseter muscles on both sides were significantly and positively correlated with the deviations from the point Menton on the frontal image, and significantly and negatively correlated with the angles of the mandibular ramus to the median line. Also a negative correlation was noted between the differences in the activity of temporal muscles on both sides and the deviations from the point Menton. 3) These results suggest that the larger the deflection of the mandible, the larger the activity of the masseter muscle on the deflective side.

Cephalometry↗
PubMed1985

Trigeminal mesencephalic neurons innervating functionally identified muscle spindles and involved in the monosynaptic stretch reflex of the lateral pterygoid muscle of the guinea pig.

Location of the neurons in the trigeminal mesencephalic nucleus innervating stretch receptors of the lateral pterygoid muscle and the mode of their synaptic connection on the lateral pterygoid motoneurons of the guinea pig were studied physiologically as well as morphologically, in comparison with the trigeminal mesencephalic neurons innervating muscle spindles in the superficial masseter muscle, with the following results: stimulation of the caudal half of the trigeminal mesencephalic nucleus evoked monosynaptic excitatory postsynaptic potentials in the ipsilateral lateral pterygoid motoneurons. Stimulation of the lateral pterygoid nerve directly evoked spike potentials in the neurons located in the caudal half of the ipsilateral trigeminal mesencephalic nucleus, which responded with increased firing to stretch, and with silent period to twitch, of the ipsilateral lateral pterygoid muscle. Averaging of intracellular potentials of the lateral pterygoid motoneurons with extracellular spike potentials of these trigeminal mesencephalic neurons revealed excitatory postsynaptic potentials after a monosynaptic latency, but no inhibitory postsynaptic potentials. Injection of horseradish peroxidase into the lateral pterygoid muscle labeled 15-20 cells in the caudal half of the ipsilateral trigeminal mesencephalic nucleus, while 174-228 cells retrogradely labeled by horseradish peroxidase were found throughout the whole rostrocaudal extent of the ipsilateral trigeminal mesencephalic nucleus following injection of horseradish peroxidase into the masseter muscle. It was concluded that neurons in the caudal half of the trigeminal mesencephalic nucleus send their peripheral processes to stretch receptors, presumably muscle spindles, in the ipsilateral lateral pterygoid muscle and that their central processes have excitatory synapses on ipsilateral lateral pterygoid motoneurons, thus comprising the afferent limb of a monosynaptic stretch reflex arc of the lateral pterygoid muscle of the guinea pig.

Animals↗
PubMed2004

Use of Theraflex-TMJ topical cream for the treatment of temporomandibular joint and muscle pain.

This randomized, double-blind study was designed to evaluate the effectiveness of the topical cream Theraflex-TMJ (NaBob/Rx, San Mateo, CA) in patients with masseter muscle pain and temporomandibular joint (TMJ) pain. Fifty-two subjects (5 males and 47 females) were instructed to apply a cream over the afflicted masseter muscle(s) or over the jaw joint(s) twice daily for two weeks. Theraflex-TMJ cream was used by the experimental group, while a placebo cream was used by the control group. The means of pain ratings were calculated prior to the application of the cream (baseline), after ten days of tx (period 1), and 15 days of tx (period 2) days of treatment and five days after stopping the treatment (follow-up). There was a significant decrease in reported pain levels from baseline in the experimental group for period 1 (p < 0.01), period 2 (p < 0.001), and follow-up (p < 0.01). For the control group, no significant differences were found between the different time periods (p > 0.05). There was evidence of minor side effects such as skin irritation and/or burning on the site of the application in two subjects in the experimental as well as two subjects in the control groups. The data strongly suggest that Theraflex-TMJ topical cream is safe and effective for reducing pain in the masseter muscle and the temporomandibular joint.

Adult↗
PubMed1989

Short-term effect of a stabilization splint on the asymmetry of submaximal masticatory muscle activity.

Ten healthy subjects continuously wore equilibrated maxillary full-arch stabilization splints in the retruded position for 7 days. The muscular activity balance of the masseter muscles during submaximal isometric clenching at 10% and 50% of the maximum voluntary contraction (MVC) did not change immediately on insertion of the splint, but was improved at the 50% level after 7 days (P less than 0.05). While the muscular balance of the anterior temporal muscles was not affected, either immediately on splint insertion, or after wearing it for 7 days, temporal muscle activity at 10% of the MVC was greater on the side to which the mandible moved from the retruded contact position (RCP) to the inter-cuspal position (ICP), both before (P less than 0.025) and after (P less than 0.01) wearing the splint. Splint removal after 7 days resulted in increased awareness of interferences in the ICP and increases in masseter muscle asymmetry (10%, P less than 0.025; 50%, P less than 0.05) when the electromyograms in the ICP after splint removal were compared with those on the stabilization splint before removal. After wearing the splint, the masseter muscle activity at the 10% level was greater on the side where premature contacts were present in the RCP (P less than 0.01). The use of masticatory muscle asymmetry indices in the evaluation of splint treatment for craniomandibular dysfunction is indicated since submaximal masticatory muscle activity is related to occlusal stability, premature contacts in the RCP and the direction of lateral slides from the RCP to the ICP.

Adaptation, Physiological↗
PubMed1991

Management of otolaryngic patients susceptible to malignant hyperthermia without dantrolene.

Malignant hyperthermia (MH) is an adverse reaction most frequently associated with the administration of halogenated inhalational anesthetic agents and the depolarizing muscle relaxant succinylcholine. Characteristic findings are a hypermetabolic state accompanied by extreme hyperpyrexia, acidosis, rhabdomyolysis, and generalized muscle rigidity, often involving the masseter muscles. Dantrolene sodium, which was approved in 1979 by the FDA for use in the prevention of MH in high-risk patients, has neurologic and gastrointestinal side effects. At the Children's National Medical Center (CNMC), 24 children identified as being at risk for the development of a MH reaction were anesthetized for otolaryngic procedures by using "non-triggering" anesthetics and without use of dantrolene sodium. These patients represent 56% of all patients at risk for MH or masseter muscle rigidity (MMR) reactions during an 8-year period at the CNMC. There were no complications. Concomitant muscle biopsies were performed, and caffeine/halothane contracture studies were completed in 18 of these patients, demonstrating 11 susceptible or equivocal responses. The data suggest that children undergoing common otolaryngic procedures who are at risk for development of MH may be safely anesthetized without the use of prophylactic dantrolene sodium.

Anesthesia↗