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PubMed1989

Electromyographic activity of the human masticatory muscles during submaximal clenching in the inter-cuspal position.

The activity patterns of the masseter and the anterior temporal muscles were studied in twenty-one healthy male subjects while clenching at 10, 20, 30, 40 and 50% of the maximum clenching level. At low clenching levels the temporal muscle activity tended to dominate, at high levels the masseter muscle activity was stronger (P less than 0.001). The asymmetry in muscle activity also depended upon the clenching level (P less than 0.001), while at each level the masseter muscle asymmetry was greater than the temporal muscle asymmetry (P less than 0.05-P less than 0.025). By comparing the electromyographic activities of the left and right side within each subject it was found that the masseter muscle with the higher electromyographic activity tended to have the larger cross-sectional area (P less than 0.01) and at the 50% clenching level it tended to be on the side with the greater number of post-canine tooth contacts (P less than 0.001).

Adult↗
PubMed1981

The changes in electrical activity of the postural muscles of the mandible upon varying the vertical dimension.

The relation between BT-EMG activity and variations of VD (1 to 41 mm of interocclusal distance) was studied in the masseter, anterior temporal, and posterior temporal muscles of eight normal experimental subjects. EMG activity was recorded with surface electrodes, and the VD was measured with a specially designed device. Recordings were performed with dynamic variations (series A) and with static variations (series B) of VD. Series A shows a gradual decrease of EMG activity starting from the occlusal position, passing through a range of maximum reduction at a certain interocclusal distance, and gradually increasing to the highest values close to maximum jaw opening. Series B shows the same progression, although it points out the exact VD at which minimum basal EMG activity is observed in each muscle studied (10 mm for the masseter muscle, 13 mm for the anterior temporal muscle, and 16 mm for the posterior temporal muscle).

Adult↗
PubMed1998

[THe Laumonier wax model of the ear (Collections of the Museums of the Anatomy Laboratory of Saints Pères, Paris)].

Authentified by the name of Laumonier (fecit), written on the zygomatic process of the temporal bone, a model in wax of the medial, middle and lateral ears, belongs to the collection of the "Musées Delmas, Orfila et Rouvière" in Paris. This model presents large dimensions with a great anatomical rightness. The entire temporal bone is represented with the upper part of the endocranial petrous bone removed in order to demonstrate the main elements of the internal ear (cochlea and semi-circular canals) and of the middle ear (malleus and incus). Also were represented the temporal muscle and temporal vessels, the emergency of right cranial nerves, the superior orbital fissura and its elements; the internal carotid artery and the internal jugular vein, the upper part of the sterno-cleido-mastoidal muscle and of the styloïd muscles; the middle internal part of the basis of the cranium with the trunk of the trigeminal nerve, the Gasser's ganglion with its trifurcation, the sigmoïd sinus. The dimensions are greater than the real size: total highness: 22 cm; total length: 46.5 cm; maximal highness of the ear cartilage: 16.5 cm; hemicranium width: about 22 cm. Thus the magnification of size is 2 or 3 if calculated on the basis of the external ear and 3 or 4 with reference to the half width of the cranium. The sample is fixed by two screws on a single wood board measuring 46.5 cm on 29.2 cm with two supplementary boards of 2.4 cm width under the two extreme of width, with a thickness of 1 cm.

Ear↗
PubMed1987

The amplitude distribution of electromyographic activity in painful masseter muscles during unilateral chewing.

The aim of this study was to investigate whether the amplitude distribution of electromyographic activity (EMG) in terms of muscular load revealed any differences between patients with painful masseter muscles and referents during the chewing of an almond and of gum. The relative masticatory forces of the masseter muscle and the anterior temporal muscle during chewing were calculated by a transformation of the muscular load levels of EMG activity (microV) to load levels of relative masticatory force (%RVC). This was done by regression in reverse of an isometric reference voluntary contraction (RVC) for EMG versus bite force biting on a bite-force sensor. The maximal bite-force values for patients and referents were similar. The relative masticatory force for chewing an almond was higher than that for gum-chewing. The peaks of the relative masticatory forces were similar for both patients and referents. During the chewing of an almond the relative masticatory forces of the masseter muscle below the peak load were higher for patients than referents. During gum-chewing the patients used higher forces than referents for 70% of the total chewing time analysed. This also applied to the anterior temporal muscle when chewing an almond. Estimates of the peak masticatory forces were calculated in newtons.

Adolescent↗
PubMed1993

Patterns of jaw reflexes induced by incisal and molar pressure stimulation in relation to background levels of jaw-clenching force in humans.

Patterns of jaw reflexes induced by periodontal stimulation were examined in ten adults. Surface electromyograms (EMGs) from the masseter and anterior temporal muscles were recorded when pressure stimulation was applied to either an incisor or a molar. Reflex responses to periodontal pressure stimulation varied, depending on the background levels of jaw-clenching force that preceded stimulation (background clenching force, BCF). At low BCF, excitatory reflexes were elicited from the jaw-closing muscles and jaw-clenching force. However, the magnitude of excitatory reflexes varied with the location of the stimulated tooth along the dentition. While excitatory reflexes were induced equally in the masseter and temporal muscles during incisal stimulation, stronger excitatory reflexes were induced in the temporal muscle than in the masseter muscle during molar stimulation. At high BCF, inhibitory reflexes in the jaw-closing muscles and jaw-clenching force were elicited in eight subjects (group A) during periodontal stimulation. However, excitatory reflexes in the muscles and force were elicited in the remaining two subjects (group B). In the subjects of group A, stronger inhibitory reflexes were elicited in the temporal muscle than in the masseter muscle, and jaw-clenching force also decreased during both incisal and molar stimulation. In the subjects of group B, the magnitude of excitatory reflexes decreased with increases in BCF.

Adult↗
PubMedDate not supplied

Infantile myofibromatosis: a case with unusual features and review of the literature.

A three-month-old boy was admitted for a slowly progressing nodule in his right chin, first recognized at birth and recently accompanied by facial paralysis. It was found to be a soft tissue mass arising in subcutaneous tissue and extending deep into the temporal muscle, causing temporal bone erosion without infiltrating the dura. Initially interpreted as mesenchymal chondrosarcoma, combined chemotherapy (PULSE-VAC) was given. Eighteen months later an additional nodule developed in the paraspinal skin. Evaluation of both lesions showed vimentin and alpha-smooth-muscle-action positivity. As the final diagnosis was multicentric infantile myofibromatosis, the child was followed up without therapy. Thirty months later, multiple osteolytic lesions appeared on the skull and long bones of the extremities. Some lesions remained stable and some regressed during two years of follow-up.

Chin↗
PubMed1990

Jaw muscle activity in relation to the direction and point of application of bite force.

This study examined the way the masseter and the anterior and posterior temporal muscles of human subjects were activated when a bite force of constant magnitude was exerted at different teeth in different defined directions. Subjects were instructed to produce a bite force of a particular magnitude (250 N) and direction (vertical, anterior, lateral, posterior, or medial) using a three-component force transducer and a feedback method. Simultaneously, the EMG activity of the muscles was registered with use of surface electrodes. Unilateral bite forces were produced at the right canine, second premolar, and second molar. In addition, a bilateral vertical premolar bite was examined for comparison of activity levels of the muscles of both sides. The results showed that, on average, the activities of the right and left side muscles did not differ in a bilateral vertical bite. Moreover, in a unilateral vertical bite, there were no significant right-left differences. For all bite force directions, more muscle activity was required for production of a constant bite force at the anterior side of the dental arch than at the posterior side. An exception to this rule was the activity of the posterior temporal muscle in a posteriorly directed bite. There was a close relationship between the direction of bite force and jaw muscle activity. Variations in activity were small for the anterior temporal muscle and large for the posterior temporal and masseter muscles. All muscles that were studied were always active, even in directions in which they could be expected to act antagonistically.

Adult↗
PubMed1994

Quantitative surface EMG of pericranial muscles. Relation to age and sex in a general population.

Quantitative EMG levels in pericranial muscles were studied in 547 subjects randomly selected from the general population aged 25-64 years. Surface EMGs of the right frontal and both temporal muscles were examined during rest and maximal voluntary contraction by a blind, standardized method. The amplitude of the EMG was expressed as the root mean square and mean rectified voltage. The power spectrum was calculated and the mean and median frequencies were extracted. During rest no significant differences were found between amplitude levels of the temporal muscles, while higher frequency levels were detected on the left side. Amplitude and frequency levels were higher in the frontal than the temporal muscles during rest, but lower during maximal voluntary contraction, probably for morphological differences. In the frontal muscle, females had increased amplitudes during rest and decreased levels during maximal voluntary contraction compared to males, indicating a higher tension at rest and a reduced number and/or size of muscle fibers in females. During maximal voluntary contraction a highly significant decrease with age was seen in amplitude and frequency in the temporal muscles. The present study is the first population study of EMG levels in pericranial muscles and constitutes the necessary basis for evaluating the EMG in tension-type headache.

Adult↗
PubMed1998

Masticatory muscle responses associated with unloading of biting force during food crushing.

The aim of this study was to evaluate masticatory muscle responses during food crushing. Electromyograms were recorded simultaneously with mandibular movement and the sound of food fracture in eight healthy adult males at the superior and inferior heads of the lateral pterygoid muscles, the anterior belly of the digastric muscle, the temporal muscle, and the masseter muscle. After fracture of the food, silent periods of the elevator muscles and excitatory responses of the depressor muscles were observed. The latency and duration of the silent periods increased significantly with increasing incisal velocity after fracture. The mean latency of the excitatory responses of the depressor muscle was stable. After the application of anaesthetic into the temporomandibular joint capsule, the excitatory response disappeared, whereas the silent period was partly maintained. These findings suggest that the excitatory response of the depressor muscle occurs via a polysynaptic reflex arc, and that several reflex arcs are involved in the development of the silent period during food crushing. An important role for the temporomandibular joint receptors is implied.

Adult↗
PubMed1994

Hyperalgesic change over the craniofacial area following urate crystal injection into the rabbit's temporomandibular joint.

The aim of this investigation was to study the characteristics of hyperalgesia and inflammatory change in the craniofacial area following the production of an acute arthritis of the temporomandibular joint (TMJ) in the rabbit. Unilateral arthritis was produced by the injection of monosodium urate (MSU) into the TMJ of the rabbits. Hyperalgesia was evaluated by the reduction in the threshold of the head-withdrawal response to pressure stimulation, and inflammatory change was determined by the quantitative Evans-blue test and light-microscopic examination of histological sections. Several hours after an injection of MSU (0.15, 0.5, 1.5 mg), hyperalgesic changes were observed over not only the MSU-administered condyle, but also over the ipsilateral masseter muscle and temporal muscle in a dose dependent manner, and lasted for more than 24 h before gradual recovery. The other craniofacial region showed no significant threshold-reduction. Although a very intense inflammatory sign was found in the region of the MSU-treated TMJ, a decreased or negative sign was found in the masseter muscle with a very low threshold. Local block of the TMJ using Bupivacaine suggested that the hyperalgesic change in the masseteric region was partly due to prolonged excitation of TMJ afferents.

Analysis of Variance↗
PubMed2005

Electromyographic evaluation of neuromuscular co-ordination during chewing in a subject with organic occlusion.

The neuromuscular co-ordination of the anterior masseter and temporal muscles during chewing has been studied. The subject analysed was 24 years old female with organic occlusion, molar and canine class 1, with 2 mm overbite and overjet, frontal disocclusion and canine protection, with no cranio-mandibular disorders. Masticatory cycles and electromyographic activity were recorded with a K6 I kinesiograph (Myotronics Inc., Seattle, WA, USA). The chewing cycles were recorded with a soft bolus and a hard bolus, on 3 consecutive days. Electromyographic analysis during masticatory cycles showed that electromyographic activity was higher in the masseter muscle homolateral to the chewing side than in the contralateral muscle, whereas the anterior temporal muscles achieved similar voltages. When chewing the hard bolus, versus the soft bolus, activity in the contralateral masseter muscle increased to a greater extent than in the homolateral masseter muscle. The results were analogous at all 3 recordings. When chewing, the subject showed good muscle co-ordination, which was constant over the 3 recordings made on 3 consecutive days. Increased activity of the contralateral masseter muscle when chewing the hard versus the soft bolus indicates the stomatognathic system's capability to adapt to load and its neuromuscular equilibrium.

Adult↗
PubMed2000

Ketamine reduces muscle pain, temporal summation, and referred pain in fibromyalgia patients.

Central mechanisms related to referred muscle pain and temporal summation of muscular nociceptive activity are facilitated in fibromyalgia syndrome (FMS) patients. The present study assessed the effects of an NMDA-antagonist (ketamine) on these central mechanisms. FMS patients received either i.v. placebo or ketamine (0.3 mg/kg, Ketalar((R))50% decrease in pain intensity at rest by active drug on two consecutive VAS assessments). Fifteen out of 17 ketamine-responders were included in the second part of the study. Before and after ketamine or placebo, experimental local and referred pain was induced by intramuscular (i.m.) infusion of hypertonic saline (0.7 ml, 5%) into the tibialis anterior (TA) muscle. The saline-induced pain intensity was assessed on an electronic VAS, and the distribution of pain drawn by the subject. In addition, the pain threshold (PT) to i.m. electrical stimulation was determined for single stimulus and five repeated (2 Hz, temporal summation) stimuli. The pressure PT of the TA muscle was determined, and the pressure PT and pressure pain tolerance threshold were determined at three bilaterally located tenderpoints (knee, epicondyle, and mid upper trapezius). VAS scores of pain at rest were progressively reduced during ketamine infusion compared with placebo infusion. Pain intensity (area under the VAS curve) to the post-drug infusion of hypertonic saline was reduced by ketamine (-18. 4+/-0.3% of pre-drug VAS area) compared with placebo (29.9+/-18.8%, P<0.02). Local and referred pain areas were reduced by ketamine (-12. 0+/-14.6% of pre-drug pain areas) compared with placebo (126.3+/-83. 2%, P<0.03). Ketamine had no significant effect on the PT to single i.m. electrical stimulation. However, the span between the PT to single and repeated i.m. stimuli was significantly decreased by the ketamine (-42.3+/-15.0% of pre-drug PT) compared with placebo (50. 5+/-49.2%, P<0.03) indicating a predominant effect on temporal summation. Mean pressure pain tolerance from the three paired tenderpoints was increased by ketamine (16.6+/-6.2% of pre-drug thresholds) compared with placebo (-2.3+/-4.9%, P<0.009). The pressure PT at the TA muscle was increased after ketamine (42.4+/-9. 2% of pre-drug PT) compared with placebo (7.0+/-6.6%, P<0.011). The present study showed that mechanisms involved in referred pain, temporal summation, muscular hyperalgesia, and muscle pain at rest were attenuated by the NMDA-antagonist in FMS patients. It suggested a link between central hyperexcitability and the mechanisms for facilitated referred pain and temporal summation in a sub-group of the fibromyalgia syndrome patients. Whether this is specific for FMS patients or a general phenomena in painful musculoskeletal disorders is not known.

Adult↗
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↗
PubMed1984

Conservative treatment of mandibular dysfunction. Clinical, experimental and electromyographic studies of biofeedback and occlusal appliances.

Two modes of treatment for mandibular dysfunction, electromyographic biofeedback and occlusal appliances, were studied. Thirty patients were randomly assigned to treatment with biofeedback or splints and it was shown that both therapies reduced signs and symptoms of mandibular dysfunction in the short and long-term perspective. An analysis of potentially useful clinical predictors of the treatment outcome indicated that laboratory diurnal biofeedback may be a useful alternative to splint therapy in cases where night-time bruxing is not the dominating feature. During biofeedback training, from the masseter or frontal muscle, the EMG activity in both muscle areas in 20 patients with acute or chronic mandibular dysfunction decreased within but not between six sessions, progressively more often for the masseter area. The results were valid irrespective of feedback or symptom duration. A simplistic neuromuscular learning model could not alone explain the positive effects on symptoms. It was shown that motivation was important. The EMG activity in the masseter area was greater during experimentally induced stress than under baseline or resting conditions, and greater in the patients than in matched controls. There was no difference between the pain side and the non-pain side. After the biofeedback training, the EMG activity during stress in the patients under identical conditions was lower and at the same level as in the controls, whose responsiveness had not changed. The anxiety level, expressed in TMAS scores, was greater in patients than in controls before but not after treatment. The influence on the integrated EMG activity in the masseter and temporal muscles after night-time use of appliances with different occlusal design was studied in 17 healthy subjects. After use of stabilisation splints, the activity in the temporal muscle was lower in the rest position and lower than after use of bite plates. The activity during gentle and maximal biting had not changed. The mean activity in a control group of 8 subjects had not changed at any functional level. A positive correlation between clinical signs and level of EMG activity in the temporal muscle in the rest position was observed in 19 patients with mandibular dysfunction. The patients also had less activity in the masseter and temporal muscles during maximal biting compared to healthy subjects. No change in EMG activity could be observed after night-time use of stabilisation splints or bite plates for six weeks, although the symptoms improved.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1991

[Mastication and the electromyographic silent period in denture wearers].

The purpose of this study is to compare the masticatory efficiency and the physiological activity of masticatory muscles among patients with removable partial dentures (R.P.D.) and patients with natural dentition. The masticatory efficiency is assessed from the duration of chewing sequences for various foods, from the first masticatory cycle to the swallowing. The physiological activity is tested by the duration of the inhibition reflex called the "silent period" (S.P.) obtained upon each muscle examined: 29 subjects are examined, 24 of them had a R.P.D.; they were divided into four groups according to the extent of their edentation; 5 control subjects have full natural dentition. The study is performed using global electromyography of the two masseter muscles and the two anterior temporal muscles. The mastication of the control subjects appears to have a regular alternance of working potential and periods of rest. The duration of the chewing sequences is determined by the nature of the food, brief for soft food, long for hard food. The mastication of patients with R.P.D. appears more irregular with a lengthening of active phases. The duration of chewing sequences is significantly longer for the control subjects. The duration of the S.P. is 19-21 milliseconds for the masseter muscles of the patients with dentures and the control patients, and 20-22 milliseconds for the temporal muscles for the same individuals. The differences of the S.P. durations between control subjects and patients with R.P.D. is never significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2003

Volume and shape of masticatory muscles in patients with hemifacial microsomia.

OBJECTIVE: To test the following hypotheses in hemifacial microsomia (HFM): (1) the volumes of the masseter, lateral and medial pterygoid, and temporal muscles are reduced on the affected versus unaffected side; (2) significant differences exist between the degrees of right-left disproportion in these four masticatory muscles; (3) circumferential shapes of the masticatory muscles are more irregular on the affected versus unaffected side; and (4) the degree of masticatory muscle right-left disproportion can be judged by the degree of ear, mandibular, or dental anomalies. SUBJECTS AND METHODS: Ten preadolescent patients with HFM were studied using facial photographs, dental casts, cephalometric and panoramic radiographs, and helical computed tomography scanning and three-dimensional reconstruction technique. Volumes of masseter, lateral and medial pterygoid, and temporal muscles on both sides were measured. Muscle volume disproportion was expressed as the affected/unaffected ratio. Muscle circumferential irregularity was expressed as the ratio between the total circumferential length and corresponding cross-sectional area. RESULTS: Masticatory muscle volumes were significantly smaller on the affected versus unaffected side. No significant differences were observed between the degrees of disproportion of the four masticatory muscles examined. Circumferential shapes of masticatory muscles were significantly more irregular on the affected versus unaffected side. There were no significant relationships of the degree of ear, mandibular, or dental anomalies in relation to masticatory muscle disproportion. CONCLUSIONS: In HFM the masseter, lateral and medial pterygoid, and temporal muscles all have a significantly smaller volume on the affected versus unaffected side, and specific muscles were not severely affected in the present subjects. Furthermore, all four muscles showed a significantly more irregular shape on the affected versus unaffected side. Finally, the severity of masticatory muscle disproportion can probably not be judged by the degree of ear, mandibular, and dental anomalies in preadolescent patients with HFM.

Adolescent↗
PubMed1989

[Effect of lingual surface inclination of maxillary canine on jaw muscle activity].

The effect of lingual surface inclination of the maxillary canine on the jaw muscle activity was investigated on five subjects. Several different metal maxillary canine risers were fabricated to change the lingual inclination. The EMG activity of the masseter and posterior temporal muscle was recorded bilaterally by means of bipolar surface electrodes simultaneously with the LED mandibular tracking device. On each subject the lateral gliding movements were carried out while maintaining the occlusal contact on the canine riser. The recorded muscle activity and mandibular gliding movements were analyzed quantitatively. During the lateral gliding, the working-side posterior temporal muscle was more active than the other three muscles. Steeper canine risers caused a reduction of the muscle activity when compared with the more flat guidance. In the gliding movement from maximum intercuspation, the temporal muscle showed more activity than the masseter muscle. However the relative relationships between the individual muscles as well as the working-side muscle and nonworking-side muscle remained unchanged with all canine risers. In the gliding movement into maximum intercuspation, the difference of the canine riser showed no consistent change in the muscle activity. In each subject, it was found that the canine riser with a moderate inclination was more comfortable to move the mandible, but no relationship between the EMG activity and his or her feeling was revealed.

Aged↗