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PubMed1989

Electromyographic biofeedback and rest position training of masticatory muscles in myofascial pain-dysfunction patients.

Twenty-four women outpatients with myofascial pain-dysfunction were divided into three groups of eight. All received bilateral masseter electromyographic biofeedback training. One group received biofeedback only; one group received additional instructions and modeling to place their jaw in the "rest" position; and one group was given a prosthetic guide that spaced the incisors 6.8 mm apart. Two 15-minute training sessions were conducted at a 1-week interval, with posttreatment assessment 2 weeks later. The instruction and prosthesis groups obtained significantly greater electromyographic reductions in masseter activity and increases in mandibular range of motion compared with the biofeedback-only group. Subjects with pain obtained a significant reduction in therapist and self-report pain ratings. The results suggest that short-term biofeedback treatment may be meaningfully augmented by procedures that place the mandible in the rest position.

Adult↗

PubMed1997

Identification of rat brainstem multisynaptic connections to the oral motor nuclei using pseudorabies virus. I. Masticatory muscle motor systems.

Oromotor behavior results from the complex interaction between jaw, facial, and lingual muscles. The experiments in this and subsequent papers identify the sources of multisynaptic input to the trigeminal, facial, and hypoglossal motor nuclei. In the current experiments, pseudorabies virus (PRV-Ba) was injected into the jaw-opening (anterior digastric and mylohyoid) and jaw-closing muscles (masseter, medial pterygoid, and temporalis) in bilaterally sympathectomized rats. Injection volumes ranged from 2 to 21 microl with average titers of 2.8 x 10(8) pfu/ml and maximum survival times of 96 h. The labeling patterns and distributions were consistent between each of the individual muscles and muscle groups. A predictable myotopic labeling pattern was produced in the trigeminal motor nucleus (Mo 5). Transneuronally labeled neurons occurred in regions known to project directly to Mo 5 motoneurons including the principal trigeminal sensory and supratrigeminal areas, Kölliker-Fuse region, nucleus subcoeruleus, and the parvicellular reticular formation. Maximum survival times revealed polysynaptic connections from the periaqueductal gray, laterodorsal and pedunculopontine tegmental areas, and the substantia nigra in the midbrain, ventromedial pontine reticular regions including the gigantocellular region and pars alpha and ventralis in the pons and medulla, and the nucleus of the solitary tract, paratrigeminal region, and paramedian field in the medulla. Thus, the results define the structure of the multisynaptic brainstem neural circuits controlling mandibular movement in the rat.

Animals↗

PubMed1977

[EPSP's of the motor neurons of cat masticatory muscles induced by stimulation of low-threshold infraorbital nerve fibers].

The effects of the infraorbital Aalpha afferents stimulation on the masseter motoneurons were investigated in cats under chloralose-nembutal anesthesia. It is found that stimuli 1.4-2.5 times threshold (T) evoke complex EPSPs in 69% of the investigated motoneurons, their latency being 2.1 +/- 0.2 ms (1.5-3.0 ms, n = 36), amplitude up to 30 mV and duration 9-15 ms. These EPSPs consist of two simpler responses produced by activation of two separate groups of afferent fibres. The short-latent EPSPs arise after activation of the infraorbital nerve by 1.1-1.5 T stimuli and have the same latency as the complex EPSP (1.5-3.0 ms) but a smaller amplitude (up to 2.0 mV) and shorter duration (up to 6 ms). The stability of these EPSPs during high frequency stimulation (120/c) and the development of facilitation and inhibition similar to those which appear in monosynaptic EPSPs in masseter motoneurons during stimulation of the 1a muscle afferents give reason to suggest that these EPSPs are monosynaptic. The slow rising rate indicates that they appear on distal dendrites of the motoneurons. The long-latent EPSPs arise with latency of 7-9 ms after activation of the infraorbital nerve by 1.1-1.5 T stimuli. Their amplitude reaches 1.5-2.0 mV and duration 7-9 ms. The long latency of these EPSPs in combination with low ability to repeat high frequency stimulation are consistent with their polysynaptic origin. It is suggested that the excitatory input from the lowest threshold Aalpha afferents of the infraorbital nerve to masseter motoneurons creates conditions for the development of a transient jaw closing reflex in response to light tactile stimulation of the cat's perioral region.

Action Potentials↗

PubMed1999

MRI examination of the masticatory muscles in the gray wolf (Canis lupus), with special reference to the M. temporalis.

We examined the head of the gray wolf (Canis lupus) using MRI methods. Although the arising surface of the M. temporalis was not so enlarged in the frontal bone, the small frontal bone did not disturb the M. temporalis from occupying the lateral space of the frontal area in the gray wolf as in the domesticated dog. In the gray wolf, it is suggested that the M. temporalis may not be well-developed in terms of size of arising area, but in the thickness of running bundles. We suggest that the dog has changed the three-dimensional plan of the M. temporalis during the domestication and that the M. temporalis has developed a large arising surface in the frontal bone and lost the thickness of belly in the frontal area in accordance with the enlargement of the frontal bone and the increase in brain size.

Animals↗

PubMed1985

Localization and morphometric analysis of masticatory muscle afferent neurons in the nucleus of the mesencephalic root of the trigeminal nerve in the cat.

Injections of horseradish peroxidase (HRP) were made into the ipsilateral temporal muscle and contralateral masseter muscle of 10 cats in order to identify and characterize neurons in the nucleus of the mesencephalic root of the trigeminal nerve that innervate muscle receptors in the orofacial periphery. Neurons labelled by HRP injections and unlabelled cells from 5 control cats were measured with a computer-based image analyzer, and their position was mapped on a stereotaxic graph. Cells that innervate the masseter and temporal muscles were identified throughout the rostrocaudal extent of the nucleus. There was no indication of a somatotopic pattern nor of a specific segregation within the nucleus for cells innervating muscle receptors. The nucleus contained small, rounded unipolar neurons located primarily in the dorsal border of the periaqueductal gray (PAG) matter in the rostral part of the nucleus and larger oval unipolar neurons which were scattered throughout the nucleus, but were predominant in the pontine portion of the nucleus. HRP injections labelled both large and small cells, as well as occasional multipolar cells. The last-mentioned tended to be located in the lateral margins of the PAG. The mean geometric values obtained for the control group were: area 552.7 microns2 perimeter 110.3 microns; maximum diameter 36.0 microns. and diameter of an equivalent circle 26.1 microns. The mean values of the labelled neurons were: area 606.6 microns2; perimeter 100.1 microns; maximum diameter 36.0 microns, and diameter of an equivalent circle 27.2 microns.

Animals↗

PubMed1990

[Quantification of tenderness of masticatory muscle].

As more dentists diagnose and treat the patient with temporomandibular disorders, muscle palpation has been recognized as a valuable diagnostic method. But this method was depended on sensibility and experience of the operator. The purpose of this study was to establish the quantification of muscle palpation by new pressure pain threshold apparatus. Pressure pain threshold (PPT) was determined by the subject when a ramp force applied to the skin changed from "pressure" to "pain". The subjects for the experiments were 90 normal males, 100 normal females and one patient with temporomandibular disorders. Total of 12 sites, anterior temporal M., posterior temporal M., superficial portion of masseter M. and deep portion of masseter M., were measured. The results obtained were as follows: 1. The females showed lower PPT than the males. 2. No difference of PPT between right and left sides was recognized in normal subject, but the significant difference in the patient. 3. PPT of the normal subjects were significantly higher in the posterior temporal M. than the other sites and lower in the superficial portion of masseter M. than the other sites.

Facial Pain↗

PubMed2005

A change of occlusal conditions after splint therapy for bruxers with and without pain in the masticatory muscles.

Bruxism has been suggested as an initiating or perpetuating factor in a certain subgroup of temporomandibular disorders (TMD), however, the exact association between bruxism and TMD remains unclear. This study aimed to demonstrate the difference in responses between bruxism and a subgroup of TMD to a full-arch maxillary stabilization splint from the standpoint of an occlusal condition. This study was conducted to verify the null hypothesis that there were no differences between bruxer groups with and without myofascial pain (MFP) with respect to the changes in occlusal conditions after the use of a splint. Thirty bruxers with MFP and 30 without MFP participated. Occlusal conditions were examined before and after splint therapy, and occlusal changes following the use of a splint were compared between the two groups. The frequency of occlusal changes after splint therapy was significantly higher in the MFP bruxer group than the non-MFP bruxer group (p < 0.05) for the occlusal conditions investigated in the present study. However, no statistical differences were found with regard to each occlusal condition. This result may show the variety of splint effects and may demonstrate a heterogeneous aspect to bruxism and myofascial pain.

Bruxism↗

PubMed1988

Increased masticatory muscle stiffness during limb muscle flaccidity associated with succinylcholine administration.

The resistance of mouth opening to a constant force of 1.7 N was measured in 44 pediatric subjects anesthetized with enflurane and paralyzed with succinylcholine or vecuronium. Measurements were made during a deep level of anesthesia before relaxant administration, immediately after the loss of the adductor pollicis muscle twitch and 45 s later. In 22 patients receiving succinylcholine, there was a significant reduction in mean mouth opening (from 16.9 +/- 2.8 to 12.6 +/- 4.3 to 13.0 +/- 4.3 mm; P less than 0.0005) and an increase in jaw stiffness (from 102.3 +/- 21.9 to 154.5 +/- 77.4 to 150.5 +/- 77.0 Nm/degree; P less than 0.02) immediately after disappearance of the evoked thenar muscle twitch, as well as 45 s later. In six patients receiving succinylcholine, measurements were continued at 1 min intervals; mouth opening reduction and jaw stiffness increase lasted up to 10 min and extended beyond the return of visible twitch. One patient had a reduction of mouth opening from 20 to less than 1 mm; his corresponding jaw stiffness changed from 83.4 to 3335.4 Nm/degree. This patient, considered by us to have masseter spasm, required several attempts at tracheal intubation due to an increased resistance to mouth opening, as did one other patient. Patients receiving vecuronium showed a significant (P less than 0.02) increase of mouth opening 45 s following loss of twitch (from 19.8 +/- 3.6 to 20.9 +/- 4.1 mm; jaw stiffness changed from 87.0 +/- 15.3 to 83.0 +/- 17.2 Nm/degree). Anesthesia and surgery proceeded normally; in most patients, in excess of 1 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1983

Localization of neurons innervating masticatory muscle spindle and periodontal receptors in the mesencephalic trigeminal nucleus and their reflex actions.

The mesencephalic trigeminal nucleus was studied in anaesthetized and curarized rabbits by recording the unitary activity through extracellular microelectrodes and identifying the constituent cell types. Two types of units were found, namely primary afferents supplying jaw raising muscle spindles and periodontal or gingival mechanoreceptors. These two groups of neurons exhibited a rostrocaudal somatotopy: the former occupied the entire rostral portion of the nucleus (A7-P2.3; trochlear decussation being taken as an arbitrary 0 level), the latter was located caudally (P3-P4.5) while the somata of both types of afferent fibres were present between P2.2 and P3. No evidence was found for representation of both tendon organs of jaw muscles and joint receptors. Among the units innervating muscle spindles, secondary afferents were largely more numerous than the primary ones. Among periodontal and gingival mechanoreceptor afferents, incisors were the most widely represented, followed by interalveolar gingiva and molars; the axonal conduction velocity ranged between 9 and 40 m/sec and between 8 and 16 m/sec for ipsilaterally and contralaterally projecting neurons, respectively. The motor responses obtained by electrical stimulation of discrete areas of the MTN confirmed the presence of a high degree of segregation between the two different populations of neurons. In fact, jaw raising movements are obtained when stimulating the area within A7 and P2 containing the somata of spindle afferent neurons, while only jaw opening movements are elicited by stimulation of the caudal levels of the nucleus. These data also show that the periodontal neurons whose somata are located in the MTN participate in the jaw opening reflex, just as the more numerous periodontal mechanoreceptors whose somata are located in the Gasser ganglion. Soma-somatic and soma-axon hillock gap junctions were found among the neurons of the MTN, particularly in the caudal third of the nucleus.

Animals↗

PubMed1984

The influence of stimulus type and stimulus strength on the silent period in human masticatory muscles.

The silent period in the jaw-closing muscles of nine healthy subjects was investigated. The stimulus types used were the open-close-clench movement (OCC), the mechanical chin tap and electrical skin stimulation. Irrespective of the jaw-closing speed for the OCC movements only the unmeasurable and single type silent periods were observed. Increasing the chin tap strength resulted in a decreasing percentage of single type silent periods and an increasing number of depressed, double and merged silent periods. The duration of the short and combined silent period was shorter for the OCC movements than for the chin taps. For the chin taps an increasing stimulus strength resulted in longer silent periods. Only the transition from hard to painful chin tap showed a slight, but significant decrease in short silent period duration. The beginning of the late inhibitory period, which could sometimes be evoked by electrical skin stimulation, coincided with the beginning of the second inhibitory phase of the chin-tap evoked double silent period. The long silent period as shown by one of the subjects cast doubt on the validity of the relationship between silent period duration and TMJ dysfunction.

Adult↗

PubMed1989

[Study on the masticatory muscle and occlusal function of temporomandibular joint dysfunction syndrome patients in adolescence].

The aims of this study was to clarify the role of masticatory and occlusal malfunction in causing the Temporomandibular joint (TMJ) Dysfunction Syndrome in adolescents. We examined the relationships between masticatory and occlusal malfunction and signs of the TMJ dysfunction by using the number of interocclusal points, occlusal interference, the dental arch models and the electromyographs. In particular, the electromyographs was examined by comparison between with at the first examination and after the adjustment of occlusal relations. The subjects were thirty-nine out patients with the TMJ Dysfunction Syndrome. The following results were obtained: 1) The number of interocclusal points in the TMJ Dysfunction Syndrome was fewer than in the normal control group. 2) In the relationships between the occlusal interference on the non-working side and pain as signs of TMJ Dysfunction, 76.9% in all subjects had reasonable relationship which recognized a causal sequence. 3) By analysis using integrated method for electromyographs, it was found that the total electric potentials in TA after the adjustment of occlusal relations tended to decrease in comparison with at the first examination, while, the ration of M was shown to have a tendency of increasing. 4) On comparing the gum chewing patterns (duration, interval, cycle) recorded from the masseter muscle, it was found that the pattern after the adjustment of occlusal relations were more stable than at the first examination. 5) The frequency of occurrence of the silent period after the adjustment of occlusal relations was higher than at the first examination. Also relationships between the change on duration of the silent period and signs of TMJ Dysfunction were found.

Adolescent↗

PubMed1986

Electromyography and bite force studies of muscular function and dysfunction in masticatory muscles.

Electromyographic (EMG) activity versus bite force was studied during a gradually increased isometric contraction up to maximal effort for patients with painful masseter muscles and referents. The masseter muscle, the anterior temporal muscle and the descending part of the trapezius muscle were chosen for the recordings. Bite force was registered with a bite force sensor placed between the first molars. The effects of double blind intramuscular injections of lidocaine and saline in the patients' masseter muscle were evaluated by EMG versus bite force and by assessment of discomfort. EMG activity during unilateral chewing was compared in terms of relative masticatory force between referents and patients by amplitude probability distribution analysis. Regression analyses showed intra-individually steeper slopes for high force levels than for low force levels for the masseter muscle. This was not observed for the anterior temporal muscle. These differences in slopes of the EMG versus force regressions for the masseter muscle and the anterior temporal muscle could be due to differences in recruitment pattern. The same intra-individual relationship between low and high force levels was found for referents and patients. An increased activity, especially among the patients, was found for the descending part of the trapezius muscle during stronger activity of the mandibular elevators. The EMG versus force relationship for low force levels of the masseter muscle was less steep after an intramuscular injection of lidocaine but not after saline. Both solutions for injection had a positive effect on the patients' assessments of discomfort one week after the injection. Three days after injection the patients who received lidocaine experienced a reduction in muscular discomfort. This reduction was not found among patients receiving saline. The amplitude probability distribution analysis revealed that the patients used greater relative masticatory forces than the referents during the chewing of an almond for all probability levels analysed below the peak load of the masseter muscles. Rough estimates of the peak masticatory forces in Newton (N) were for chewing an almond 364 N (referents); 373 N (patients) and for gum-chewing 239 N (referents); 238 N (patients) as regards the masseter muscle. The values were similar for the anterior temporal muscle.

Bite Force↗

PubMed1982

Masticatory muscle activity before and after elimination of balancing side occlusal interference.

The activity of the masseter and anterior and posterior temporal muscles was studied by electromyography (EMG) in the thirteen subjects with unilateral balancing side interferences and in twelve control subjects without such interferences. In both groups the EMG recordings were made during postural activity and various functions of the masticatory system and in the interference group they were repeated on two occasions following occlusal adjustment. The postural muscle activity was significantly lower in the interference than in the control group while there was no difference during maximal bite. The number of chewing cycles was somewhat longer in the interference than in the control group. During swallowing of water the maximal mean voltage amplitude was smaller in the interference than in the control group. The findings are discussed in relation to previous results and the conflicting ideas concerning occlusal factors in the aetiology of mandibular dysfunction.

Adult↗

PubMed1990

[Experimental studies on the influences of physical properties of foods on the appearance of silent period in discharge of masticatory muscles].

UNLABELLED: It is considered that the appearance of Silent Period (SP) during food crushing may relieve tissue injury caused by sudden change of maxillo-mandibular impactive force. In connection with this phenomenon, the relation between changes in vertical velocity of mandibular movement and the appearance of SP during food crushing was investigated. In addition, efforts were made to clarify the influences of lack of periodontal pressoreceptive information on the appearance of SP. Subjects were ten males (aged 24 to 31) with natural dentition and no masticatory dysfunction. Electromyograms were recorded on 4 lead locations: the central parts of each masseter and the anterior bundles of each temporal muscle. A Mandibular Kinesiograph and electromyograph were used to record simultaneously mandibular movement and myoelectric discharge during food crushing for the sake of comparing changes in mandibular position, vertical velocity of mandibular movement and muscular activity. Eight kinds of foods of various textures were selected for use in the examinations: dry macaroni, rice cracker, raw carrot, pickled thistle root, pickled radish, raisin, synthetic rubber block and softened chewing gum. The food was positioned on the occlusal table of the lower first molar on the habitual masticatory side of each subject. Then the subject was required to close his mouth rapidly to crush the food at a single masticatory stroke. Two experimental conditions were established in order to clarify the significance of periodontal pressoreceptive information on the appearance of SP: (1) normalcy and (2) infiltration anesthesia of the periodontal tissues of the upper and lower first-molar region on the habitual masticatory side. Results 1. SP appeared during a single masticatory stroke in response to sudden decreases or increases of vertical velocity of mandibular movement. 2. The frequency of the appearance of SP depends on the crushing characteristics of the food which is tested. For softened chewing gum and the synthetic rubber block, only one SP occurred; two SPs occurred in the cases of pickled radish and raisin; three SPs in the cases of raw carrot and pickled thistle root; and more than four SPs in the cases of dry macaroni and rice cracker. 3. Lack of periodontal pressoreceptive information resulting from anesthesia had no effect on the appearance of SP. CONCLUSIONS: 1. Sudden changes in vertical velocity of mandibular movement may depend on the crushing characteristics of the food which is crushed.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed2002

Relationship between the number of occlusal contacts and masticatory muscle activity in healthy young adults.

The electromyographic (EMG) potentials of left and right masseter and temporalis anterior muscles were recorded in 23 healthy young adults during: 1. a 3-second maximum voluntary clench (MVC) on cotton rolls positioned on the posterior teeth (standardized recording); and 2. a 3-second MVC in intercuspal position. EMG potentials recorded in intercuspal position were standardized as a percentage of the mean potentials of the standardized recording, and the EMG muscle activity was calculated. The number of occlusal contacts in intercuspal position was assessed by using eight microm thick shim stocks. Two groups of subjects with either 1. Less than ten occlusal contacts (11 subjects with "few contacts"); or 2. At least ten occlusal contacts (12 subjects with "many contacts") were selected. The MVC muscle activity in the "few contacts" group was significantly lower than that recorded in the "many contacts" group (p<0.005). In conclusion, the number of occlusal contacts and masticatory muscular function are significantly related, at least in young adults with a sound stomatognathic apparatus.

Adult↗

PubMed1996

Craniofacial bone remodeling in growing rats fed a low-calcium and vitamin-D-deficient diet and the influence of masticatory muscle function.

Fifty-two male growing rats were randomly divided into three groups. The first group (n = 18) received a hard deficient diet, and the second (n = 18) a soft deficient diet. The control group (n = 16) was fed the normal hard diet. At the beginning and in the middle of the 28-day experimental period oxytetracycline was injected. Two representative coronal sections of the snout and the corresponding contact microradiographs were analyzed. The bone mass of the premaxillary and nasal bones seemed to be less in the two deficient diet groups than in the normal one, due to an increased endosteal bone resorption and decreased bone formation. No difference in the bone apposition rate and pattern could be seen between the deficient hard and soft diet groups, except in the dorsal part of the premaxilla, where the bone formed in the first half of the experiment was markedly more resorbed in the deficient soft diet group during the remaining period than in the deficient hard diet group. The morphology of the sutures was influenced by the altered function, since the sutural space became narrower, and premature obliterations of the internasal suture were observed in the deficient soft diet group. In conclusion, poor bone quality was observed in the skull of rats fed a low-calcium and vitamin-D-deficient diet, with less bone mass than in normal conditions. Masticatory function was a significant factor influencing bone remodeling and sutural growth even in situations in which a metabolic bone disturbance exists.

Animals↗

PubMed1977

Integrated actions of masticatory muscles: simultaneous EMG from eight intramuscular electrodes.

In 29 normal persons with complete dental arches, the muscular activity of the temporalis, masseter, medical pterygoid, anterior belly of the digastric, mylohyoid and geniohyoid muscles was studied electromyographically with bipolar fine wire electrodes during various mandibular movements--both resisted and unresisted. Action potentials were recorded on FM magnetic tape and each experiment was also videotaped. Temporalis muscle was active during centric closing of the jaw with either contact of the teeth, or against resistance; during free lateral movements to the ipsilateral side, either against resistance or occlusal contact; during incisor gum chewing, molar gum chewing on ipsilateral or contralateral sides, during normal mastication; and during forceful centric occlusion. Activity occurred in the masseter and medial pterygoid muscles during the following movements; closing the jaw slowly either without occlusal contact or with occlusal contact and against resistance; free lateral movement to contralateral side, either against resistance or with occlusal contact; protraction of the jaw either without occlusal contact or with occlusal contact; swallowing either saliva or water; incisor gum chewing with either the ipsilateral or contralateral molars; normal mastication; and during forceful centric occlusion. Activity occurred in the digastric, mylohyoid and geniohyoid muscles during the following movements; opening of the jaw either slowly or maximally against resistance; closing the jaw against resistance; free lateral movement to ipsilateral and contralateral sides, either against resistance or with occlusal contact; protraction against resistance of the jaw either without or with occlusal contact; swallowing saliva and water; and protraction of the tongue. They work in antagonism (reciprocally) during gum chewing and normal mastication.

Action Potentials↗

PubMed1992

Masticatory muscle fatigue: endurance times and spectral changes in the electromyogram during the production of sustained bite forces.

The purpose of this experiment was to determine if the characteristics of fatigue observed in the limb muscle system are also evident in the muscles of mastication, specifically, the masseter and temporalis. Surface electrodes were placed bilaterally over the masseter and temporalis muscles of 10 adults. Each subject was instructed to maintain maximal and six levels of submaximal incisal bite forces for as long as possible. The power density spectrum of the electromyographic signals for each muscle was calculated at the onset and failure of the task. The decrease in endurance time with an increase in bite force followed a pattern similar to that in limb muscles, and each muscle was characterized by a consistent reduction in the mean power frequency of the power density spectrum and a variable change in r.m.s. power. The variability of changes in r.m.s. power (which is inconsistent with changes found in the limb muscles) was explained in terms of either changes in motor-unit firing rate or the muscle's relative contribution to the generation of bite force. The analyses also demonstrated a curvilinear relationship between bite force and r.m.s. power, but no relationship between bite force and the mean power frequency of the power density spectrum.

Adult↗