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PubMed2000

The effect of a cholecystokinin agonist on masseter muscle activity in the cat.

The CCK(B) agonist, pentagastrin, has been shown to induce anxiety in human subjects. Similarly, in the cat model, pentagastrin facilitates the expression of hypothalamically activated emotional behavior. Because hypothalamically mediated emotional behavior is also accompanied by increased EMG activity in the jaw muscles, these experiments were designed to examine the combined effects of administration of pentagastrin with activation of hypothalamically mediated emotional behavior upon jaw muscle EMG activity. Electrodes were carefully lowered through previously placed guide tubes overlying the hypothalamus until a behavioral site was identified. Following the establishment of a stable threshold current for eliciting an emotional behavioral response, the skin overlying the ipsilateral masseter muscle was shaved and cleaned with alcohol, and surface electrodes were attached. The EMG was recorded, amplified, digitized, and stored in a microcomputer for analysis. Mean power frequencies (MPF) and latencies for behavior were calculated for baseline prior to infusion of all drugs. Following this, the effects of intravenous administration of pentagastrin and the CCK(B) antagonist LY288513 on the MPF were determined. The infusion of the CCK(B) agonist, pentagastrin (0.77, 1.92, and 3.84 microg/kg), decreased MPF in a time-related manner. The effects of pentagastrin 1.92 microg/kg were blocked by the CCK(B) antagonist, LY288513 (6.54 microg/kg). In addition, the infusion of LY288513 alone increased MPF. These results are surprising in that pentagastrin's anxiogenic properties would appear to make it likely to facilitate motor activity, not suppress it.

Animals↗
PubMedDate not supplied

[Electromyography recording of the silent period in masseter muscles in persons with total dental prostheses with various vertical occlusal dimensions].

Silent period is reflex pause or period suppressed activity after some kind of simulation during or after muscular contraction. In dentistry electromyographically registered silent period has important place as method of functional diagnosis. The aim of this investigation was to establish duration of silent period in both masseter muscles of persons with complete dentures in normal increased and decreased occlusal vertical dimensions. Subjects of investigation were 4 men and 4 women, average of 65 years. Occlusal vertical dimensions were established electromyographically. For every subject tree sets of complete dentures were made: with normal, increased and decreased occlusal vertical dimension for 4 mm. Silent period was registered by "Medlec" Mystro-MS 20 apparatus with intramuscular leads. The differences of silent period duration were registered among all three vertical dimensions, especially between and increased occlusal vertical dimensions.

Aged↗
PubMed1985

Influence of vertical dimension on masseter muscle electromyographic activity in patients with mandibular dysfunction.

Occlusal splints were adjusted to different vertical heights and used to single out the influence of vertical dimension of occlusion in increments on BT-EMG activity of the masseter muscle in patients with mandibular dysfunction. The vertical dimension of least EMG activity was determined for each of 60 patients, who were randomly divided into three groups according to the vertical dimension at which the occlusal splint was adjusted: group No. 1, 1 mm from occlusal vertical dimension; group No. 2, mean vertical dimension, 4.25 mm; group No. 3, mean vertical dimension, 8.25 mm. Results showed a significant reduction of masseter BT-EMG activity (series A and B) at the end of the 3-week treatment period for patients in group Nos. 2 and 3 in comparison with group No. 1. Furthermore, the short-term use of occlusal splints with a vertical height that exceeded the so-called physiologic interocclusal distance did not result in an increase in masseter BT-EMG activity. This study suggests that an increase of vertical dimension of occlusion to or near the vertical dimension of least EMG activity by means of occlusal splints can be an effective way to obtain a reduction in masseteric muscle activity.

Adolescent↗
PubMed1989

Variability in electromyographic surface recordings of the human masseter muscle.

Serial registrations of integrated unilateral surface masseter EMG were performed in eight healthy subjects in the rest position, during controlled gentle biting and during maximal clenching at five different sessions in order to analyse the variability. The recording conditions were standardised. The EMG activity for the group did not differ significantly between the sessions at any level but individual variations were great in the rest position both within and between days. Good consistency was found at controlled force levels. Temporally stable measurements of masseter activity which permit quantitative comparisons thus seem possible.

Adult↗
PubMed1990

Frequency analyses of EMG power spectra of anterior temporal and masseter muscles in children and adults.

To study the functional change of masticatory muscles during growth and development, frequency analyses of surface electromyogram (EMG) power spectra were carried out. The subjects were six children (five males and one female), aged 4.5 +/- 0.2 years, having full deciduous dentition (Hellman's dental age IIA) and six adults (four males and two females), aged 27.7 +/- 3.8 years, having full permanent dentition. EMG signals were recorded bilaterally by using bipolar silver-surface electrodes from the anterior temporal and masseter muscles while the subjects were chewing gum and while performing maximum clenching in the intercuspal position. A fast Fourier transform algorithm was used to obtain the power-spectral density function and the power spectra of the EMG signals. Since the total power value from 62.5 to 1000 Hz was 100 percent, the frequencies at 25, 50, 75, and 90 percent of the cumulative power were calculated. The results showed that the frequencies at every percent of the cumulative power were age-dependent and that the EMG power spectra patterns in adult muscles were shifted to significantly lower frequencies than those in child muscles. The shift was probably caused by differences in the proportion of fiber type and fiber size between muscles of children and adults.

Adult↗
PubMed1976

Cutaneous silent period in masseter muscles: a clinical and electrodiagnostic evaluation.

In 35 normal subjects electromyographic silent periods were constantly evoked bilaterally in the masseter muscles during maximal contraction after unilateral electrical stimulation over the infraorbital or mental nerve. Findings in this study and data obtained in 30 patients suffering from trigeminal (26) and facial (four) nerve lesions suggest that the silent period evoked according to our methods is cutaneous in origin. The trigeminal sensory root forms the afferent limb of the silent period reflex. Its central pathway is thought to pass both crossed and uncrossed through the pons. Determination of the cutaneous silent period might be of value for the demonstration of trigeminal nerve lesions and to supplement results concerning other brain-stem reflexes.

Adolescent↗
PubMed1977

Degenerative changes in masseter muscle following injection of lidocaine: a histochemical study.

Changes in succinic dehydrogenase, adenosine triphosphatase, and phosphorylase activities occurred in masseter muscle by 15 minutes following injection of 2% lidocaine. Abolishment of phosphorylase activity suggested an effect on the sarcoplasmic reticulum. Increased staining for succinic dehydrogenase and adenosine triphosphatase activities suggested damage to mitochondria and myofibrils, respectively. Leucine aminopeptidase and glucose-6-phosphate dehydrogenase activities appeared in macrophages.

Adenosine Triphosphatases↗
PubMed1976

The silent period in the masseter muscle of patients with TMJ dysfunction.

The silent period (SP) following a jaw jerk elicited during sustained contraction in the masseter muscles has been studied in two groups of subjects, one with and one without, acute and distinct symptoms of TMJ dysfunction. The subjects with acute TMJ dysfunction symptoms showed significantly shorter latency and longer duration of the silent period and the period of their depressed activity (DA) was also significantly longer than in the group without TMJ dysfunction. The duration of the SP of both muscles was symmetrical in about 60% of subjects in each group. This study validates that the duration of the silent period may be a useful diagnostic tool of clinical interest.

Action Potentials↗
PubMed1992

Bite-force development, metabolic and circulatory response to electrical stimulation in the canine and porcine masseter muscles.

The development of fatigue was investigated by electrical stimulation in 15 domestic pigs (1 yr old, 70-90 kg body weight) and seven adult dogs (3 yr old, 45 kg body weight). After anaesthesia, silver electrodes were implanted in the anterior and posterior parts of the right masseter muscles. The contralateral muscle was used as control. The bite force was measured. Muscle biopsies were obtained from the anterior, central and posterior parts, and were immediately frozen in liquid nitrogen. A fluorometrical analysis by enzymatic methods for glycogen, glucose, creatine phosphate, NAD, NADH, lactate and pyruvate was made. Blood flow was measured by 133Xe wash-out; oxygen consumption was monitored with an oxygen electrode. The porcine masseter was continuously stimulated for 60 min (100 V, 4 Hz and 2 ms). The canine masseter was intermittently stimulated (100 V, 20 Hz and 2 ms). The contraction was repeated four times, with a 10-min rest between. The porcine masseter could sustain longer endurance times than the canine masseter, which was easily fatigued. A marked substrate depletion was evident. The precontractional contents of glycogen, glucose and creatine phosphate were reduced. Lactate accumulation was evident (2-4 times more in the porcine and 4-8 times more in the canine masseter). The NADH concentration increased and the NAD content decreased. Blood-flow impairment (80% reduction in the dog, 60% in the pig) was observed. After the contraction phase, there was a hyperaemia (58% elevation of blood flow in the pig masseter, 45% in the canine). The oxygen tension followed in magnitude and time the blood-flow changes. These circulatory variables returned to normal after recovery. The high degree of substrate depletion, blood-flow impairment and a simultaneous decrease in oxygen transport to the contracted muscle, in combination with a prominent lactate accumulation, may induce a decrease in bite-force production.

Animals↗
PubMed1982

[Extraction and purification of slow myosin from the masseter muscle of Ovis aries].

Ovis aries masseter is a typical muscle consisting of slow-twitch fibres. The muscle homogeneity is well evidenced histochemically by the myosin ATPase reaction. The extraction and purification of myosin from sheep masseter is reported. After its centrifugation and dialysis followed by ion-exchange chromatography, the protein analysed on SDS polyacrylamide gels showed the usual pattern of slow myosin. The light-chain LC2 was present as a double band, a fact which has already been reported and which could be ascribed to SH group oxidation. From the present data sheep masseter can be considered a good source of slow myosin, and we have used it satisfactorily in the preparation of specific antibodies.

Adenosine Triphosphatases↗
PubMed2000

Bilateral effect of a unilateral occlusal splint on the expression of myosin heavy-chain isoforms in rat deep masseter muscle.

Many studies have shown that various myosin isoforms are involved in muscle contraction. A search for specific antibodies directed against the myosin heavy chain (MHC) resulted in the identification of at least two main classes, referred to as MHC type I and type II. In this study, immunohistology and gel electrophoresis were used to determine the proportion of MHC isoforms in rat deep masseter muscle at different times after the insertion of an unilateral occlusal splint. An increasing proportion of MHC type I isoforms was found in both deep masseters soon after splinting, and this trend continued until 7 days after splint insertion. The type I fibres were clearly distributed on either side of the central axis of the muscle. At 15 days, a significant decrease in the percentage of the type IIb MHC isoform was observed on the occlusal splint side compared to the contralateral side. After 30 days of unilateral splinting, the proportion of type IIb fibres on the splint side returned to baseline whereas on the contralateral side there was an increase in the proportion of this type. The results suggest an initial adaptation after the unilateral occlusal disturbance in which muscles of both sides react in the same way; later, the muscles of each side adapt their expression of MHC isoforms according to altered functional demand.

Adaptation, Physiological↗
PubMed1986

Changes in neuromuscular reflexes in the masseter muscles during functional jaw orthopedic treatment in children.

Masseteric reflexes following standardized taps on an upper incisor were recorded electromyographically (1) in children with Class II, Division 1 malocclusions at different times before and during the treatment with the Bionator functional appliance and (2) during an observation period in control subjects who were not being treated. In each experimental session, 72 taps were delivered during clenching at 10% of the maximal electromyographic output. Statistical criteria provided by a previously developed computer program allowed the objective determination of inhibitory and excitatory periods in the electromyographic output following the stimulus, which together constitute the poststimulus electromyographic complex (PSEC). The influence of the change in occlusal relations on the PSEC was determined in ten subjects by comparing pretreatment results with those obtained after 1, 3, and 6 months of treatment. Concurrent with an improvement of the sagittal jaw relation in the patients with a pronounced disharmony, a short latency excitatory peak appeared in their PSECs. It was demonstrated by averaging nonrectified electromyographic activity that this peak was brought about through synchronization of motor units. In the control group, however, the morphology of the PSEC was reproducible over time. Successful functional therapy is thus accompanied by specific transient changes in the reflex response of the masseter muscles to standardized tooth taps. The neural pathways contributing to these observations originate in periodontal and muscular receptors, and might provide a clue for the mechanism underlying successful functional treatment.

Activator Appliances↗
PubMed2000

Capsaicin-induced muscle hyperalgesia in the exercised and non-exercised human masseter muscle.

AIMS: Strong jaw muscle exercises such as tooth grinding in sleep bruxism are frequently believed to be a predisposing factor in myogenous types of temporomandibular disorders. However, it is not known whether tooth grinding in sleep bruxism is associated with increased sensitivity to intramuscular stimuli. This study therefore compared the hyperalgesic effects of an intramuscular injection of capsaicin into the right masseter with and without a prior experimental tooth-grinding exercise. METHODS: Ten healthy men participated in 2 randomized sessions (exercise, non-exercise session) separated by 1 week. In the exercise session, 0.1 mL capsaicin (100 micrograms/mL) was injected into the right masseter immediately after 45 minutes of experimental tooth grinding. In the non-exercise session, the exact same paradigm was used, except that the experimental tooth grinding was omitted. The perceived intensity of pain evoked by intramuscular capsaicin was scored on a 100-mm visual analog scale (VAS). Pain detection thresholds (PDTs) to pressure stimuli and maximal voluntary occlusal force (MVOF) were measured before capsaicin injection; 5, 15, and 45 minutes after the injection; and once a day for the following 3 days. RESULTS: Injections of capsaicin into an exercised or non-exercised masseter did not cause significant differences in peak pain intensity on the VAS (57 +/- 6 mm in exercised masseter vs. 53 +/- 6 mm in non-exercised masseter; P = 0.464). The PDTs in the exercised masseter were significantly decreased for up to 1 day after the capsaicin injection (P < or = 0.038), whereas PDTs in the non-exercised masseter were decreased for only 5 minutes (P = 0.017). The MVOF on the right side was decreased 5 minutes after the capsaicin injection in both sessions (P < 0.010). The MVOF on the left side was significantly reduced for up to 15 minutes after the capsaicin injection in the exercise session only (P < 0.019). CONCLUSION: Increased sensitivity to percutaneous pressure stimuli probably reflects a post-exercise muscle soreness following tooth grinding, whereas intramuscular sensitivity to noxious chemical stimuli immediately following exercise seems to be unchanged.

Adult↗
PubMed2000

Electromyography of the anterior temporalis and masseter muscles of owl monkeys (Aotus trivirgatus) and the function of the postorbital septum.

Anthropoids and tarsiers are distinguished from all other vertebrates by the possession of a postorbital septum, which is formed by the frontal, alisphenoid, and zygomatic bones. Cartmill [(1980) In: Evolutionary Biology of the New World Monkeys and Continental Drift. New York: Plenum, p 243-274] suggested that the postorbital septum evolved in the stem lineage of tarsiers and anthropoids to insulate the eye from movements arising in the temporal fossa. Ross [(1996) Am J Phys Anthropol 91:305-324] suggested that the septum insulates the orbital contents from incursions by the line of action of the anterior temporal muscles caused by the unique combination of high degrees of orbital frontation and convergence. Both of these hypotheses must explain why insulation of the orbital contents could not be achieved by decreasing the size of the anterior temporal musculature with a corresponding increase in size of the remaining jaw adductors, rather than evolving a postorbital septum. One possibility is that the anterior temporalis is an important contributor to vertically directed bite forces during all biting and chewing activities. Another possibility is that reduction in anterior temporal musculature would compromise the ability to produce powerful bite forces, either at the incisors or along the postcanine toothrow. To evaluate these hypotheses, electromyographic (EMG) recordings were made from the masseter muscle and the anterior and posterior portions of the temporalis muscles of two owl monkeys, Aotus trivirgatus. The EMG data indicate that anterior temporalis activity relative to that of the superficial masseter is lower during incision than mastication. In addition, activity of the anterior temporalis is not consistently higher than the posterior temporalis during incision. The data indicate relatively greater activity of anterior temporalis compared to other muscles during isometric biting on the postcanine toothrow. This may be due to decreased activity in superficial masseter and posterior temporalis, rather than elevated anterior temporalis activity. The anterior temporalis is not consistently less variable in activity than the superficial masseter and posterior temporalis. The EMG data gathered here indicate no reason for suggesting that the anterior temporal muscles in anthropoids are utilized especially for incisal preparation of hard fruits. Maintenance of relatively high EMG activity in anterior temporalis across a wide range of biting behaviors is to be expected in a vertically oriented and rostrally positioned muscle such as this because, compared to the posterior temporalis, superficial masseter and medial pterygoid, it can contribute relatively larger vertical components of force to bites along the postcanine toothrow. The in vivo data do not support this hypothesis, possibly because of effects of bite point and bite force orientation.

Animals↗
PubMed1978

Mast cells in masseter muscle in experimental bruxism in man.

Three human subjects performed tooth grinding for 25 min, and after 20 h biopsies of the right and left masseter muscles were examined for their contents of mast cells. In comparison with specimens from a control group of three subjects, there was an increase of degranulating mast cells in muscles that had performed bruxism.

Adult↗
PubMed1994

Reflex responses of motor units in human masseter muscle to mechanical stimulation of a tooth.

The reflex responses evoked by controlled mechanical stimulation of an upper central incisor tooth in single motor units in the human masseter muscle were examined. The stimuli were (brisk) taps and (slow) pushes of about 2 N peak force, applied orthogonally to the labial surface of the ipsilateral upper central incisor tooth. The reflex responses of the motor units were characterised by analysis of the changes in the durations of the first and second interspike intervals (ISIs) immediately following the stimulus. A significant increase in the duration of these ISIs in comparison with pre-stimulus ISIs indicated inhibition, and significant shortening indicated excitation. Twenty masseter motor units were tested with both the pushes and the taps. The brisk taps elicited a significant reflex inhibition in 16 of the 20 motor units at a latency of 13 ms and duration of 37 ms. This inhibition was followed by significant excitation in 11 of the 20 units at latencies of 71 ms, lasting for 29 ms. The short-latency response to slow pushes was significant inhibition in four units: significant excitation in one unit and no response in 15 units. The slow pushes evoked a significant long-latency excitatory reflex response in 12 of the 20 units at latencies of 77 ms and lasting for 40 ms. The shapes and amplitudes of the compound post-synaptic potentials underlying the reflex responses in the motoneurones were estimated. It is concluded that stimulation of periodontal mechanoreceptors usually activates an excitatory reflex pathway to the jaw-closing motoneurones. This probably helps to grip the food bolus between the teeth during chewing. However, when the rate of application of the stimulus is large enough, a short-latency inhibitory response is evoked which, if of sufficient duration, may over-ride the subsequent excitatory response. Inhibition of the jaw-closing muscles will tend to protect the teeth and soft tissues when one bites unexpectedly on a hard object while chewing.

Adult↗