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PubMed1982

EMG activities of masticatory muscles during licking in rats.

EMG activities of the jaw closers and the jaw opener were recorded during licking of water and varying taste solutions in rats. The rats showed a continuous and rhythmic licking pattern (about 7 Hz) when they took water, 0.5 M sucrose and 0.1 M NaCl. A clear reciprocal relation of the jaw closers and opener was recognized during licking. The digastric muscle (jaw opener) started to work about 60 msec before the contact of the tongue with the liquid and ceased its activity at the moment of the contact, while the temporalis and masseter muscles (jaw closers) started to work about 50 msec after the contact. On the other hand, the rats rejected 1 M NaCl and 5 X 10(-4) M quinine-HCl, and stopped licking within a few seconds. However, EMG activities of the masticatory muscles continued more than 20 sec after cessation of licking. A characteristic jaw opening (gaping) was observed after licking quinine or after an oral infusion of 0.3 M CaCl2. To presentations of 0.03 M HCl and 0.3 M NaCl, the licking pattern was the intermediate between the above-mentioned licking patterns shown by acceptable and rejective taste stimuli, i.e., the rats tended to show intermittent lickings to these HCl and NaCl solutions and the interlick interval varied greatly. The present results suggested that licking patterns and EMG activities of the masticatory muscles were characterized by the hedonic aspect or palatability of taste (acceptance-rejection dichotomy) rather than the taste quality (whether a taste is sugar, salt, acid, etc.).

Animals↗
PubMed2004

Characteristics of the sarcoplasmic reticulum Ca2+-dependent ATPase from masticatory muscles.

We compared the sarcoplasmic reticulum (SR) Ca-ATPase from masseter (M) and medial pterygoid (MP) muscles with that from fast muscles (FM) to examine whether its calcium transport capability and enzymatic activity are different. SR vesicles from FM, M, and MP muscles were obtained according to Champeil et al.(1985). Assays for characterization of the enzyme properties were performed. The results showed similar optimal conditions for the Ca-ATPase activity and calcium transport in M, MP, and FM. However, the maximal values of calcium transport, Ca-ATPase activity, and K(i) for thapsigargin were significantly lower in the masticatory muscles. These findings are likely related to different Ca-ATPase isoforms. Since the local anesthetics used in dentistry inhibit Ca-ATPase and calcium transport in FM, it will be important for the effects of these drugs on the Ca-ATPase of masticatory muscles to be assessed.

Animals↗
PubMed1983

Masticatory muscle transposition in primates: effects on craniofacial growth.

The effects of early transposition of the masticatory muscles on the craniofacial growth and development of infant primates are documented with the aid of serial cephalometry, EMG's, and dry-skull preparations. The bilateral posterior transposition of the insertion of the masseter and temporalis muscles was followed by a significant superior and anterior rotation of the midfacial growth pattern as well as by marked skeletal morphological changes. The study documents the ability to change skeletal craniofacial growth patterns by altering muscle attachments.

Animals↗
PubMed2005

Activity patterns of the masticatory muscles during feedback-controlled simulated clenching activities.

In 10 normal subjects, the electromyographic (EMG) activities of the masseter, anterior and posterior temporalis, medial pterygoid, inferior lateral pterygoid, as well as the anterior digastric, were bilaterally recorded during clenching with various resulting force vectors. The intraoral force transfer was achieved with a three-component force transducer. The direction and magnitude of the force vectors were controlled by visual feedback. The goal of the study was to investigate how various clenching directions at constant magnitude of force influence the EMG activity in the masticatory muscles during gradual increase of the horizontal force component. Depending on the force direction and the individual muscle, an increase or decrease of activity was observed during clenching with increasing horizontal force components at constant magnitude of force. The inferior lateral pterygoid exhibited the highest activation (about 80% of maximal voluntary clenching) of all masticatory muscles. The medial pterygoid showed the greatest range of variation in activation behavior, and it was the most active muscle in relation to all clenching directions. In conclusion, the results show that with growing horizontal force components at constant magnitude of force, all muscles demonstrated an increase or decrease of activity in several clenching directions.

Adult↗
PubMed2001

Masticatory muscle activity assessment and reliability of a portable electromyographic instrument.

STATEMENT OF PROBLEM: Masticatory muscle hyperactivity is thought to produce muscle pain and tension headaches and can cause excessive wear or breakage of restorative dental materials used in the treatment of prosthodontic patients. The quantification and identification of this type of activity is an important consideration in the preoperative diagnosis and treatment planning phase of prosthodontic care. PURPOSE: This study investigated the quantification process in complete denture/overdenture patients with natural mandibular tooth abutments and explored the reliability of instrumentation used to assess this parafunctional activity. MATERIAL AND METHODS: The nocturnal EMG activity in asymptomatic complete denture/overdenture subjects was assessed with and without prostheses worn during sleep. Because of the large variance within and between subjects, the investigators evaluated the reliability of the 3 instruments used to test nocturnal EMG activity in the sample. RESULTS: Electromyographic activity data of denture/overdenture subjects revealed no differences between prostheses worn versus not worn during sleep but demonstrated a very large variance factor. Further investigation of the instrumentation demonstrated a consistent in vitro as well as in vivo reliability in controlled laboratory studies. CONCLUSION: The portable EMG instrumentation used in this study revealed a large, uncontrollable variance factor within and between subjects that greatly complicated the diagnosis of parafunctional activity in prosthodontic patients.

Analysis of Variance↗
PubMed2004

MR features of masticatory muscles in adenoid cystic carcinoma involving the masticator space.

Adenoid cystic carcinoma (ACC) is known for its slow-growing but severely infiltrative nature with little tissue reaction. Although the masticatory muscles are often involved, their imaging features have not been well elucidated. We hereby report three patients with widespread ACC, which initially appeared with trismus and/or temporomandibular symptoms and involved the masticator space. Possible features of masticator space involvement are presented on magnetic resonance (MR) images. Masticatory muscle changes on MR images consisted of two aspects, namely, denervation changes and direct tumour invasion.

Adult↗
PubMed1993

Comparison of psychologic and physiologic functioning between patients with masticatory muscle pain and matched controls.

This study explored the physiologic and psychologic distinctions between masticatory muscle pain patients and age and sex-matched normal controls. Subjects completed several standardized psychologic tests. They then underwent a laboratory stress profile evaluation to obtain physiologic measures (EMG, heart rate, systolic and diastolic blood pressure) under conditions of rest, mental stress, and relaxation. The pain patients reported greater anxiety, especially cognitive symptoms, and feelings of muscle tension than did the controls. Under stress, pain patients had higher heart rates and systolic blood pressure than the controls. Electromyogram activity in the masseter regions was not significantly different between the pain and control group. The results are discussed in terms of the likely mechanisms that might account for the observed differences between masticatory pain patients and normal subjects.

Adult↗
PubMed1990

Mandibular movement trajectories and masticatory muscle activities in the rabbit in the sleep and wake states.

Jaw movements and masticatory muscle activities were recorded in freely moving rabbits. During 5 hours of continuous recording, three states were recognized, namely, sleep, rhythmical jaw movements, and wake without any major jaw movements. The rhythmical jaw movements included chewing, drinking, and grooming and were similar in characteristics to those recorded in immobilized animals. During sleep, two kinds of masseter muscle behaviors with jaw movement features were recorded: one characterized by a short EMG bursts and a pause in jaw movements, considered similar to clenching, and the other characterized by cyclic bursts and lateral jaw excursion, a grinding-like movement. The latter was correlated with light sleep, thus suggesting a resemblance between the grinding-like behavior and bruxism.

Animals↗
PubMed2004

Variation in daily masticatory muscle activity in the rabbit.

The daily use of masticatory muscles remains largely unclear, since continuous recordings were limited in space and time. This study's purpose was to use radio-telemetry to examine daily muscle use and its inter- and intra-individual variations. A telemetric device was implanted into the rabbit masseter, and the transmitted signals were digitally stored for 7 days. Muscle use was analyzed by calculation of the total time each muscle was activated above 5, 20, and 50% of the day's peak activity. Rabbits (n = 6) spent only 2% of the time chewing. Muscles were activated up to 20% of the total time at levels exceeding 5% of peak activity, and only about 0.5% of the time in forceful behaviors utilizing 50% of maximum contraction. It can be concluded that daily muscle use remained constant during succeeding days, but differed significantly among muscle regions and individuals.

Analysis of Variance↗
PubMed1989

[Influence of occlusal contact on jaw movement and masticatory muscle activity].

Jaw movement in six degree-of-freedom and 8 ch EMG of masticatory muscles were studied in 9 subjects to investigate the influence of occlusal contact on jaw function. The results are as follows. 1. The border jaw movement and the chewing movement changed according to the change of occlusal contact. 2. The tooth contact on balancing side is not good for jaw function because of two following reasons. First, tooth contact on balancing side limited the border jaw movement. Second, tooth contact on balancing side decreased jaw closing muscle activities of non-chewing side. 3. Existence of craniomandibular control system that controls jaw function under the influence of central nervous system and peripheral system was suggested.

Adult↗
PubMed1978

Correlative study of pain perception and masticatory muscle reflexes in man.

An attempt was made to explore the possibility of using the masticatory muscle reflexes as pain indices in human subjects. It was found that the digastric reflex, so readily evoked by electrodental stimulation in experimental animals, could not be consistently elicited in man. The reflex silent period of the masseteric muscles, on the other hand, may be used as a pain index for evaluating dental analgesia, provided that analgesic interference is anticipated at points along the reflex arc.

Adult↗
PubMed2004

Influence of masticatory muscle pain on electromyographic activities of cervical muscles in patients with myogenous temporomandibular disorders.

The present study tested the hypothesis that the resting electromyographic (EMG) activities of sternocleidomastoid and trapezius muscles of myogenous temporomandibular disorder (TMD) patients would be significantly greater than healthy individuals. Eight masticatory muscle pain patients without disc interference disorders (DID) and 30 patients with DID along with 41 matched control subjects were included in the study. The resting EMG activities of sternocleidomastoid and trapezius muscles were recorded with a portable EMG machine. Pain intensities described over the muscles were recorded with a 100 mm visual analogue scale. The two groups of patients had significantly higher resting activities compared with control subjects. Patients (in both groups) who had pain in sternocleidomastoid and trapezius muscles reported significantly higher resting activities in the respective muscles than patients who were free of pain and the controls. The presence of pain over the examined muscles showed significant association with the myogenous TMDs without DID. The observed association of the cervical muscles with myogenous TMDs is expected to be a result of functional link between masticatory and cervical muscles. The present findings suggest that the myogenous TMDs without DID could be a distinct sub-group that can be a part of broader regional or generalized diseased entity.

Adult↗
PubMed1996

Effects of masticatory muscle function on bone mass in the mandible of the growing rat.

The effect of altered masticatory muscle function on bone mass at different sites in the rat mandible was studied using aluminium as a reference substance in computer-assisted image analysis. Forty-two growing male rats were divided into three groups, of which one group was killed at the beginning of the experiment to provide baseline values. Of the remaining two, one received a hard diet (control group) and the other a soft diet. After 28 days the rats were killed and the mandibles were excised. Lateral radiographs were taken of the mandible halves together with an aluminium stepwedge and then analysed by an image analysis system. Radiographic bone mass was measured in the transverse plane as "aluminium-equivalent thickness' in millimetres. Standardized areas were chosen to investigate regions with different functional demands. Significant differences were found between the groups in the alveolar bone of the molars and the incisor, as well as in the condylar costa and the condylar process. Significant differences were also found in some areas related to muscle insertion, such as the anterior lower border of the ramus, whereas no statistically significant differences could be found in others, such as the posterior lower border of the angular process. In conclusion, altered masticatory function influences the amount of bone mass in certain parts of mandible, where changes in applied bending forces have possibly altered the bone strain.

Animals↗
PubMed2006

Organisation of common inputs to motoneuron pools of human masticatory muscles.

OBJECTIVE: To determine the pattern of organization of common inputs to the motoneuron pools of individual muscles in the masticatory system. METHODS: Six subjects bit on a rubber-coated wooden splint placed between the upper and lower incisor teeth. We recorded the surface electromyogram (EMG) of co-contracting masseter, temporalis and digastric muscles bilaterally during isometric jaw closing at 5%, 10%, 20% and 40% of maximal voluntary masseter EMG. RESULTS: The cross-correlograms of the EMGs of homologous muscle pairs indicate that there are common synaptic inputs to the motoneuron pools of the left and right masseter, and left and right digastric muscles, but not to left and right temporalis. The amplitude of the central peak in masseter and digastric correlograms increased with bite force. When the activity of ipsilateral muscle pairs was cross-correlated, central peaks were prominent for masseter-digastric and masseter-temporalis muscle pairs, and the peak amplitudes increased significantly with bite force. In contrast, no significant central peak was observed for temporalis-digastric muscle pairs at any level of voluntary biting. CONCLUSIONS: We conclude that there is synchronous modulation of input bilaterally to the masseter muscles and to the digastric muscles but not to the temporalis muscles. There is synchronous modulation of input to ipsilateral masseter-digastric and masseter-temporalis muscle pairs but not to temporalis and digastric muscles. SIGNIFICANCE: The extent of common input to motoneuron pools of muscles acting around a common joint varies for different muscle pairs, and is not simply a function of whether the muscles of the pair are synergists or antagonists.

Adult↗