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PubMed1998

Short-term reproducibility of pressure pain thresholds in masticatory muscles measured with a new algometer.

The purpose of this project was to test the within-day and between-days reproducibility of a new and inexpensive algometer. Twelve symptom-free men and nine women participated. Pressure pain thresholds (PPTs) of the bilateral masseter and temporalis muscles were assessed during four sessions (mornings and afternoons of days 1 and 3). During each session, each palpation point of the masticatory muscles was measured four times. There was an interval of only a few seconds between measurements 1 and 2, and between measurements 3 and 4, respectively, while at least 5 minutes of rest were allowed between measurements 2 and 3. The PPT values between the morning and afternoon sessions and between days 1 and 3 were not significantly different. When the within-session reproducibility for all muscles was considered, only the PPT values between measurements 2 and 4 were not significantly different. Analysis of variance showed that the interindividual variability of PPT was 1.4 to 6.8 times higher than the variability observed within or between sessions and days. No gender difference was found.

Adult↗
PubMed2006

An impact of masticatory muscle function on IL-1beta and SOX9 expression in condyle.

The importance of masticatory muscle function on the growth and differentiation of condyle was examined. The aim of this study was to investigate how reduced masticatory muscle function influences intrinsic regulatory factors which govern growth and differentiation of condylar cartilage. Masseter muscles of 3-week-old Wistar rats were resected bilaterally. Masseteric resected animals and corresponding control animals were sacrificed at 3, 6, 12 and 21 days post-resection. The condyles were then processed for histological and immunohistochemical analysis. The expression patterns of an inhibitory regulator (IL-1beta) and a master regulator (Sox9) of chondrogenesis in condylar cartilage of growing rats were investigated. Quantitative analysis shows that masseteric resection significantly increased the number of IL-1beta positive cells in proliferative layer. In contrast, the number of Sox9 positive cells was significantly decreased compared to the control animals. It can be concluded that the reduced articular function due to masseteric resection decreased condylar cartilage cell differentiation which led to the decrease in the thickness of condylar cartilage.

Animals↗
PubMed2005

MRS assessment of glutamate clearance in a novel masticatory muscle pain model.

The injection of 1.0 M glutamate into the masseter (jaw-closer) muscle results in a short period of muscle pain (5-10 min) and a prolonged period of mechanical sensitization (> 30 min). It is unclear, however, whether there is a temporal relationship between intramuscular glutamate concentration and either muscle pain or mechanical sensitization. In the present study, (1)H MRS and electrophysiological recording of masticatory muscle nerve fibers were performed in order to monitor glutamate clearance and nerve fiber activity, respectively, after injection of glutamate into rat masticatory muscles. Glutamate signal amplitude was found to decay rapidly (half-life t 1/2 = 108 +/- 42 s), and became indistinguishable from the baseline 10 min after the injection. Glutamate-evoked nerve fiber activity was also found to decay rapidly (t 1/2 = 76 +/- 28 s). These results suggest that glutamate clearance correlates well with the time course of glutamate-evoked muscle pain fiber discharge.

Animals↗
PubMed1997

Dynamics of the human masticatory muscles during a jaw open-close movement.

The movements of the human jaw are controlled by the forces produced by the masticatory muscles. As the jaw moves, these muscles change in length and their force producing units, the sarcomeres, change in length simultaneously. The lengths and length changes of the sarcomeres are determinants for the forces they are able to produce. Hence, masticatory muscle force and jaw movement influence each other which makes it difficult to study their mutual relationship. In this paper, lengths and contraction velocities of the sarcomeres of the human jaw-opening and jaw-closing muscles are presented as well as the consequences for force production during jaw open-close movements simulated with a biomechanical model. Jaw-opening muscles acted almost synchronic in terms of sarcomere length, contraction velocity and force production. They were able to produce the largest isometric forces at relatively small jaw openings at the cost of reduced force production capabilities in wide open positions. In contrast, the jaw-closing muscles acted more differently. They were able to sustain active muscle force throughout a large range of the closing movement. Within this group the masseter and medial pterygoid contracted excentrically during a short time. The lateral pterygoid muscle portions behaved differently with respect to both groups. The jaw-opening muscles produced negligible passive forces during jaw closing. The passive forces of the jaw-closing muscles, however, contributed significantly to a limitation of the jaw-opening movement.

Humans↗
PubMed2002

[Influence of the relaxation splint and stabilization splint on the EMG parameters of the masticatory muscles].

OBJECTIVE: To explore the influence of the type of occlusal splint on the masticatory muscles (TA,MM). METHODS: TA and MM EMG during ICP maximal clenching were recorded in 20 dentate normal subjects, when they weared no occlusal splint, relaxation splint and mandibular stabilization splint. RESULT: With the insertion of relaxation splint and mandibular stabilization splint, the EMG parameters of TA and MM during ICP maximal clenching was dramatically reduced (P<0.05). CONCLUSION: The relaxation splint and mandibular stabilization splint can relax the masticatory muscles.

English Abstract↗
PubMed2003

Quantification of masticatory muscle atrophy after high-dose radiotherapy.

PURPOSE: To determine the rate of change in the cross-sectional area of the masticatory muscles after radiotherapy. METHODS AND MATERIALS: Eligible patients had undergone unilateral radiotherapy between 1993 and 2000 and had a baseline CT scan, a comparable follow-up CT scan a minimum of 1 year later, and no recurrence of cancer. Fourteen patients had their CT series scanned into digital image files. Two anatomically selected CT slices were bisected by the midline sagittal plane and stored under randomly assigned file names. Three observers measured the masseter and medial pterygoid areas on two occasions. RESULTS: The intraobserver reliability of the muscle area measurements was 96.3% for the masseter and 97.1% for the medial pterygoid. The interobserver reliability of the muscle area measurements was 96.7% for the masseter and 96.3% for the medial pterygoid. On the treated side, the muscles received a median dose of 56 Gy (range 47-63) in 2.0-0.4-Gy fractions. With a median follow-up of 2.9 years (range 1-7.6), mixed-effects regression analysis demonstrated a significant area of reduction of -0.17 cm(2)/y (p = 0.0001) for the masseter and -0.13 cm(2)/y (p = 0.001) for the medial pterygoid. The controlled rate of muscle atrophy was 3.9%/y (95% confidence interval 1.4-6.4) for the masseter and 2.3%/y (95% confidence interval -0.6 to 5.1) for the medial pterygoid. CONCLUSION: Standard therapeutic radiation doses appear to cause significant masticatory muscle atrophy.

Adult↗
PubMed1991

Stretch-based relaxation and the reduction of EMG activity among masticatory muscle pain patients.

This study explored the efficacy of stretch-based relaxation procedures for the reduction of muscle activity in the masseter regions of subjects diagnosed with masticatory muscle pain disorders. Thirty-four subjects with elevated masseter activity were assigned randomly to either a postural relaxation/rest experimental group or a stretch-based relaxation experimental group. Following a psychosocial stressor and application of the relaxation procedure, persons in the stretch-based group showed greater reductions in EMG activity than did those in the postural group for the right masseter region (t = 1.94, P less than .04) and the left masseter region (t = 2.07, P less than .03). The results are discussed in terms of the implications of these findings for further research concerning the etiology and treatment of masticatory muscle pain.

Adult↗
PubMed2004

Efficacy of stabilization splints for the management of patients with masticatory muscle pain: a qualitative systematic review.

This study aimed at providing an answer to two clinical questions related to patients with masticatory muscle pain: 1) Does the use of a full-coverage hard acrylic occlusal appliance (stabilization splint) lead to a significant decrease of symptoms? and 2) Is the treatment success achieved with a stabilization splint more pronounced than the success attained with other forms of treatment (including placebo treatment) or no treatment? A systematic search was carried out in different electronic databases, supplemented by handsearch in four selected dental journals and by examination of the bibliographies of the retrieved articles. Thirteen publications, representing nine controlled clinical studies, could be identified. Reporting quality of most studies as assessed with the Jadad score ranged from 1 to 5. Based on the currently best available evidence it appears that most patients with masticatory muscle pain are helped by the incorporation of a stabilization splint. Nevertheless, evidence is equivocal if improvement of pain symptoms after incorporation of the intraoral appliance is caused by a specific effect of the appliance. A stabilization splint does not appear to yield a better clinical outcome than a soft splint, a non-occluding palatal splint, physical therapy, or body acupuncture. The scarcity of current external evidence emphasizes the need for more and better clinical research.

Clinical Trials as Topic↗
PubMed2005

Influence of functional appliances on masticatory muscle activity.

The purpose of the present study was to investigate the influence of an activator appliance and a spring active appliance on masticatory muscle activity by means of electromyography (EMG). Twelve adult males with good general health were recruited as subjects. Three functional appliances were used in each subject for long-period EMG recording during daytime and sleep and short-time EMG recording during voluntary biting. Following findings were obtained. (1) The activity of all muscles was greater during biting than during daytime and sleep, (2) the muscle activities tended to increase in the digastric muscle and to decrease in the temporal muscle with activators under all conditions, and (3) the temporalis-masseter ratios became lower with the biting use of appliances. Therefore, this study suggests that functional appliances should be used during sleep and during the day in combination with voluntary biting to achieve adaptation and development of the masticatory muscles.

Adaptation, Physiological↗
PubMed2002

Influence of masticatory muscle function on transverse skull dimensions in the growing rat.

AIM: The aim of this study was to elucidate the influence of reduced masticatory muscle function on the transversal dimensions of the premaxilla, maxilla (including the dental arch) and the calvaria in the growing rat. MATERIAL AND METHODS: 38 growing male albino rats were used. 14 animals were killed at the beginning of the experiment to provide baseline values (Young Group). The remaining animals were randomly divided into two equal groups; one received the ordinary diet in hard pellet form (Hard Diet Group), and the other a soft diet (Soft Diet Group). The experimental period started when the rats were 28 days old and had a duration of 28 days. 3D measurements of the dentofacial skeleton were performed on dry skulls with a Reflex microscope. RESULTS: No inter-group differences were found in mean body weight and overall length of the cranium. The dental arch was found to be narrower in the third molar region in the Soft Diet Group, possibly due to less growth in the midpalatal suture and/or to reduced occlusal loading. This may be due to the first and second molars having been in occlusion at the beginning of the experimental period, while the third molars were not. Furthermore, the premaxilla and the frontal bones at the most lateral part of the temporal crest were narrower in the Soft Diet Group, these regions being areas of masticatory muscle attachment.

Animals↗
PubMed1988

Quantitative electromyography of the masticatory muscles of Pteropus giganteus (Megachiroptera).

Mastication has been studied by cinematography and quantitative electromyography while flying foxes, Pteropus giganteus, were freely feeding on standardized pieces of apple, soaked raisin, and banana. The primarily orthal mandibular movements are caused by mainly bilaterally symmetrical firing of all the masticatory muscles. Asymmetric activity in the superficial and deep masseter and medial pterygoid causes slight protrusion early in opening. Slight lateral deviations at the end of opening and at the start of closing are caused by asymmetric and asynchronous activity in the pterygoids and digastrics, and by asynchronous firing of the deep temporalis and zygomaticomandibularis. Food consistency affects movement characteristics as well as characteristics of muscular activity. In this study electromyograms were digitized and the number of spikes and mean amplitude per interval (set by the filming rate) recorded. Although a significant correlation exists between descriptors, the product thereof appears to be the best predictor of certain kinematic variables (cycle length and maximum excursion of the mandible). On the other hand, the changes in magnitude of muscular activity as a function of the position of a cycle in the reduction sequence and as a function of food consistency are more translated in a variation of the mean amplitude than in a variation of the number of spikes per interval. Observed variation differs among muscles studied. It is most apparent in the superficial and deep masseter and least in the temporalis and zygomaticomandibularis. Late cycles of apple and raisin mastication are long and exhibit large gapes but almost no anterior movement. The adductor activity frequently shows a synchronized, pulsatile pattern leading to an unfused tetanus.

Animals↗
PubMed1990

[The influences of habitual side chewing and the character of food on the masticatory muscle activity in children].

The purpose of this study was to investigate the influences of habitual side chewing and the characteristics of food on the masticatory muscle function in children. A total of thirty persons were subjected to the study; 10 with deciduous dentition (designated as G1), 10 with mixed dentition (as G2), 10 with permanent dentition (as G3), none of whom had any gnatho-facial dysfunction. EMGs were recorded from the temporal anterior muscles and masseter muscles on both sides, and the mandibular movement on the frontal plane was recorded during chewing of boiled fish cake paste, chewing-gum and chewing of dried cuttlefish on both the habitual side and the non-habitual side. EMG activities obtained and periods of closed phase, occlusal phase and open phase in the pathway of the mandibular movement were measured with a personal computer system. The relationship between the total muscle activities at clenching in the intercuspal position and the total muscle activities at chewing were also evaluated. The results obtained in the present study were as follows: 1) Influence of habitual side chewing on the rhythm of the mandibular movement during chewing of chewing-gum was not found in all groups. Influence on EMG activities was not found in G1 and G2, but were presented in G3. 2) Influence of the character of food on rhythm of mandibular movement was not clear in G1, but as found in the other groups, while EMG activities were influenced by the character of food in all groups. 3) The MA Index (the ratio of total muscle activities while chewing to total muscle activities at clenching) showed a decrease with age. As far as the results of the present study is concerned, it could be suggested that the proficiency of the chewing ability is dependent on the dentitional growth. Furthermore, the MA Index was considered to be appropriate for evaluating the masticatory muscle function in children.

Child↗
PubMed1994

[Effects of occlusal position on masticatory muscle activity].

The effects of different occlusal position on the masticatory muscle function were investigated on 5 subjects. Two types of maxillary stabilization splints were fabricated in order to change the occlusal position. One type of the splints was to increase the occlusal height and the other was to shift the occlusal position laterally. The EMG activities of the masseter (M) and the anterior and posterior temporal muscles (AT, PT) were measured in various occlusal positions at 50% of maximal voluntary activity of the M and AT. The results were as follows: 1. When the occlusal height was increased. 1) The activity of the PT decreased in most subjects. 2) Asymmetry index (AI) of each tested muscle did not always indicate a similar value. 2. When the occlusal position was shifted laterally, 1) The activities of the ipsilateral AT and PT were higher than those of the contralateral side. 2) The AI of the AT and the PT changed gradually when the occlusal height was large while they changed greatly near the intercuspal position (IP) when the occlusal height was smaller. Therefore, the symmetry of the temporal muscle activity was thought to be influenced sensitively by the lateral shift of jaw position near the IP.

Adult↗
PubMed2001

Rhythmic masticatory muscle activity during sleep in humans.

Rhythmic Masticatory Muscle Activity (RMMA) is frequently observed during sleep in normal subjects and sleep bruxers. We hypothesized that some normal subjects exhibit RMMA at a lower frequency than sleep bruxers. Polysomnographic data from 82 normal subjects were compared with data from 33 sleep bruxers. RMMA episodes were defined as three or more consecutive bursts of masseter EMG activity, with or without tooth-grinding. Such episodes were observed in nearly 60% of normal subjects. A lower frequency of episodes was noted in normal subjects than in bruxers. Sleep organization was similar between groups. Bruxers had twice as many masseter muscle bursts per episode and episodes of higher amplitude compared with controls with RMMA. The high prevalence of RMMA observed in normal subjects suggests that this activity is related to certain sleep-related physiological functions, including autonomic activation.

Adolescent↗
PubMed1999

Electromyography of the perioral and masticatory muscles in orthodontic patients with atypical swallowing.

Subjects with an open bite and an atypical swallowing pattern before (n = 20) and after (n = 10) orthodontic treatment and subjects with a normal swallowing pattern (n = 15) were examined. The electromyographic (EMG) activity of the upper and lower lips in the region of the modiolus and of the mentalis, masseter and temporal muscles was evaluated during the swallowing of saliva and of water and after the chewing of peanuts as well as during maximal biting in intercuspal position. During swallowing the atypical swallowers exhibited larger EMG activities of the perioral muscles and smaller EMG activities of the masticatory muscles than the control subjects. During maximal biting in intercuspal position, major EMG activity of the masseter and temporal muscles and minor EMG activity of the perioral muscles were recorded in both groups. No normalization of the electromyographic swallowing pattern could be observed during orthodontic treatment (closure of the open bite).

Adolescent↗
PubMed1997

Serotonergic neurons in the caudal raphe nuclei discharge in association with activity of masticatory muscles.

There is a dense serotonergic projection from nucleus raphe pallidus and nucleus raphe obscurus to the trigeminal motors nucleus and serotonin exerts a strong facilitatory action on the trigeminal motoneurons. Some serotonergic neurons in these caudal raphe nuclei increase their discharged during feeding. The objective of the present study was to investigate the possibility that the activity of these serotonergic neurons is related to activity of masticatory muscles. Cats were implanted with microelectrodes and gross electrodes. Caudal raphe single neuron activity, electrocorticographic activity, and splenius, digastric and masseter electromyographic activities were recorded during active behaviors (feeding and grooming), during quiet waking and during sleep. Seven presumed serotonergic neurons were identified. These neurons showed a long duration action potential (> 2.0 msec) and discharged slowly (2-7 Hz) and very regularly (interspike interval coefficient of variation < 0.3) during quiet waking. The activity of these neurons decreased remarkably during fast wave sleep (78-100%). Six of these neurons showed tonic changes in their activity positively related to digastric and/or masseter muscles activity but not to splenius muscle activity during waking. These data are consistent with the hypothesis that serotonergic neurons in the caudal raphe nuclei play an important role in the control of jaw movements.

Animals↗
PubMed1989

[A clinical study on the relationship between chewing movements and masticatory muscle activities].

Chewing movement is one of the most important functional and physiological jaw movements, and it is coordinated by the three elements of the functional occlusion system (teeth, TMJs and masticatory muscles). However, the relationship between chewing movement and these elements has not been clarified. The purpose of this study was to investigate the relationship between chewing movement and the activity of the masticatory muscles which directly control jaw movements. 25 subjects with normal stomatognathic function, 5 patients with MPD syndrome (muscle dysfunction group) and 5 patients with unilateral TMJ internal derangement (TMJ dysfunction group) were selected. 6 gums with different hardness were used as the test bolus. Sirognathograph Electromyograph Analysing System was used to simultaneously record chewing movements and electromyograms of the right and left masseter, anterior temporal, posterior temporal and anterior belly of digastric muscles. Using the analysing software which was developed for this study, chewing movements and muscle activities were analysed. The results were as follow; A. In normal subjects 1. Gum hardness influenced durations of the closing and occluding phases, maximum opening and closing speed, opening degree and deviation of opening and closing path. 2. Gum hardness influenced muscle activities except of the time factors of digastric bursts. 3. Durations of the closing and occluding phases were found to be related with the elevator muscle activities. Maximum closing speed was related with the masseter and anterior temporal muscle activities. Deviation of closing path was related with the anterior and posterior temporal muscle activities. B. In abnormal subjects 1. The changes mainly observed in the muscle activities were found to be significantly different between the muscle dysfunction group and normal group. Similarly, the changes mainly observed in the chewing movements were different between the TMJ dysfunction group and normal group. 2. When compared with the relationships in normal subjects, changes were observed in the relationships for closing movement in the muscle dysfunction group. In contrast, changes were observed in the relationships for opening movement in the TMJ dysfunction group. From the results, close relationships were found between chewing movements and muscle activities, and were characteristically influenced by stomatognathic dysfunction.

Adolescent↗