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PubMed1993

The immediate effect of the variation of anteroposterior laterotrusive contacts on the elevator EMG activity.

A unilateral maxillary splint divided into three occlusal blocks was built for eight healthy young adults. The three blocks allowed the anteroposterior location of the laterotrusive contacts to vary and to distribute the occlusal force over equivalent periodontal surfaces. The ipsilateral masseteric and temporalis electromyogram (EMG) activities were recorded with surface electrodes during maximal voluntary clenching. The elevator EMG activity with the anterior occlusal block in place was significantly lower than with the intermediate or posterior blocks. The reduction for both elevators with the intermediate block in place did not show a significant variation in comparison to the posterior block of the three blocks inserted. The elevator activity with the three occlusal blocks did not differ from that recorded with the posterior block alone. Neurophysiologic and biomechanical explanations are given related to this laterotrusive elevator muscular behavior.

Adult↗
PubMed1986

Electromyographic screening of myogenous and arthrogenous TMJ dysfunction patients.

Sixty patients, clinically examined for TMJ dysfunction, were also electromyographically screened. The TMJ dysfunction pain in forty patients was evaluated to be mainly of a myogenous origin and in fourteen patients of a mainly arthrogenous origin. Due to lack of findings in the clinical examination six patients were not to be classified into either of the two groups. They were excluded from the EMG study. For the EMG examination the patients were asked to clench for 30 s in the intercuspal position at 50% of the maximum EMG activity of the masseter muscles. Surface electromyograms of the right and the left masseter and anterior part of the temporalis muscles were monitored. The amplitude of the EMG signal, the duration of the silent period and the changes in the frequency composition of the signal during the 30 s contraction were analysed. Statistically significant differences between the two patient groups were found in EMG amplitude and in silent period duration. However, the difference in silent period duration was due to the dependency of the silent period on the activation level of the muscle. No statistically significant difference in silent period was found when this dependency was corrected for in the data. The EMG parameters related to muscular fatigue phenomena did not show any difference between the two groups. The difference in EMG amplitude and consequently the difference in silent period duration support the clinically made distinction into mainly a myogenous or mainly an arthrogenous origin of TMJ dysfunction pain.

Adult↗
PubMed1987

Limited mandibular mobility and potential jaw dysfunction.

This investigation studied relationships between signs and symptoms of potential mandibular dysfunction and limitations of maximum active depression and maximum active lateral excursion of the mandible in young adult males. Mouth opening capacity was not associated with symptoms and signs thought to be clinically indicative of the status of the mandibular locomotor system. Limitations of mandibular lateral excursions, on the other hand, were associated with signs and symptoms of potential mandibular dysfunction, but not with signs and symptoms from the temporomandibular joints.

Adult↗
PubMed1989

Spectral analysis of the masseter and anterior temporalis: an assessment of reliability for use in the clinical situation.

The electromyogram (EMG) of contracting muscles can be analysed in the frequency domain by spectral analysis. However, there is a need to establish the reproducibility of spectral parameters such as mean power frequency (MPF). This study examined the variation of MPF (masseter and anterior temporalis) between and within recording sessions. The MPF was found to be significantly reliable for both muscles, but considerable within-subject variation was found despite comprehensive measures to standardize recording methods and conditions. It is concluded that MPF may have clinical application in the diagnosis and treatment of patients with facial pain arising from muscle dysfunctions, but caution should be exercised in interpreting small changes in frequency, given the inherent variability of MPF.

Adult↗
PubMed1990

An electromyographic study of aspects of 'deprogramming' of human jaw muscles.

Surface electromyograms from the right and left masseter and anterior temporalis muscles were used to detect peripheral correlates of deprogramming, also known as programming and reprogramming, of jaw elevator muscles. Putative deprogramming was attempted through the clinically recommended use of a leaf gauge, placed for 15 min between the maxillary and mandibular anterior teeth and disoccluding the posterior teeth by about 2 mm. Studied contractile activities were those of postural activity (subconscious, semi-isometric, minimal activity) and intercuspal teeth clenching (conscious, isometric, maximal activity). Use of the leaf gauge did not affect normalized postural activity (about 4%), the duration (about 900 ms) and static work efforts of clenching (about 1200 microV.s), the time to peak mean voltage of clenching (about 400 ms), and the peak mean voltage of clenching (about 300 microV). Activity and asymmetry indices showed that the studied motor innervation patterns were not changed by the leaf gauge.

Adult↗
PubMed1991

Observations on the motor control of brief teeth clenching in man.

Without artificial feedback control, maximum voluntary isometric contractions were performed for about 1 s by six subjects. Randomly selected surface electromyograms of the anterior temporalis and masseter muscles suggested that, in some cases, the motor control of the entire isometric contraction might have been preprogrammed through the phenomenon of anticipation. In the majority of cases, the control of the initial contraction phase might have been preprogrammed, followed by a phase of servo-controlled motor activity. As a functional basis for the servo-control of isometric force generation, it was suggested that compartmentalized 'extrafusal and intrafusal motor units' were recruited and decruited in an orderly manner, and periods of alpha-motor inhibition were interpreted as signs of switching from one control scheme to another, possibly via a transcortical loop.

Adult↗
PubMed1992

Exteroceptive suppression of temporalis muscle activity in various types of headache.

Exteroceptive suppression (ES) of temporalis muscle activity, particularly the multisynaptic ES2, has been reported to be significantly reduced in tension type headache, but not in migraine. We re-evaluated the methods of optimally analysing the single shock technique and its intra- and inter-individual variability in 26 normal subjects. These data were compared with the results in patients with migraine, post-lumbar puncture headache, headache due to meningitis, tension-type headaches in HIV infection and patients with symptomatic headache of various etiologies. ES2 was absent in about 50% of tension-type headache patients, but only in one normal subject. With the methods used here and when patients with absent ES2 were excluded, mean duration of ES2 was not significantly different between the various groups. It seems therefore necessary, in spite of increased discomfort for patients, to use complementary methods, such as averaging 16-32 responses and applying various stimulation sets, if one wants to increase the potency of temporalis ES2 as a diagnostic and pathophysiologic tool in headache.

Adult↗
PubMed1992

Occlusal control of mandibular elevator muscles.

Occlusal stability and mandibular elevator muscle function was studied in 25 women (20-30 yr of age). They had 27-32 fully erupted teeth with few treated occlusal surfaces, and craniomandibular function including mandibular mobility was normal. The aim was to analyze the influence of natural patterns of occlusal contact on electromyographic activity, unaffected by pain and functional disorders. Occlusal stability was assessed in the intercuspal and in lateral contact positions as the number of teeth with physical contact and the number of opposing pairs of teeth in contact. Electromyographic activity was recorded by surface electrodes over anterior and posterior temporalis and masseter muscles. In general, positive correlations were found between occlusal stability in intercuspal position and moderate to strong static and dynamic contractions, most significant in masseter muscles, indicating that forceful contraction of these muscles implies stable occlusion. Systematically, the duration of activity during chewing was negatively correlated with occlusal stability in the intercuspal position, most pronounced in working-side muscles. This pointed to shorter contractions with stable occlusion and is interpreted as the result of less need for stabilizing activity. It is concluded, that the correlations between occlusal stability and elevator muscle function are probably based on feedback mechanisms from periodontal pressoreceptors.

Adult↗
PubMed1981

Jaw-muscle activity during speech with the mandible fixed.

Electromyographic recordings were made from the anterior temporalis, masseter, medial pterygoid, and lateral pterygoid muscles in four normal adult subjects. Discrete bursts of activity occurred in these muscles even during speech with the jaw prevented from moving by placement of a bite block between upper and lower molars. The bursts of muscle activity with the bite block were similar in frequency of occurrence, time of peak activity, and magnitude to the activity observed with the jaw free to move. A motor control system that employs a central simulation process to coordinate the lips and tongue with the jaw is not necessarily consistent with this finding. An efficient central simulation process might be expected to eliminate the discrete jaw-muscle activity with the jaw fixed as well as producing correct responses in the lips and tongue. These data are more consistent with a motor control system employing lower-level neural mechanisms to coordinate articulatory movements.

Action Potentials↗
PubMed1994

Pathophysiology of hemimasticatory spasm.

Two patients aged 21 and 50 years presented with facial hemiatrophy and unilateral spasms of the masticatory muscles. Masticatory muscle biopsy showed normal findings in both patients and facial skin biopsy specimens only showed atrophy, although morphoea (localised facial scleroderma) had been diagnosed nine years previously in the second patient. The involuntary movements consisted of brief twitches and prolonged contractions clinically and electromyographically similar to those of hemifacial spasm and cramps. The jaw jerk and the silent periods were absent in the affected muscles. Direct stimulation of the muscle nerve and transcranial stimulation of the trigeminal root demonstrated slowing of conduction and after-activity due to autoexcitation. Observations in other reported cases and these two patients suggest that hemimasticatory spasm is produced by ectopic activity secondary to focal demyelination of the trigeminal motor nerve fibres. The proposed cause of the neuropathy is focal damage to the masticatory nerves caused by compression, possibly resulting from the deep tissue changes that occur in facial hemiatrophy.

Adolescent↗
PubMed1984

Relationships between masticatory muscle cross-section and skull shape.

Cross-sectional areas of the masseter, temporalis and medial, and lateral pterygoid muscles were determined in 16 subjects by means of computer tomography. In each subject three scans were made, intersecting the thickest part of the muscles at right angles to the fiber direction. The masseter and medial pterygoid muscles are large in persons with brachycephalic skulls, short faces, and a small jaw angle. The cross-sectional areas of the temporalis and lateral pterygoid muscles showed no correlation with facial dimensions.

Adult↗
PubMed1989

Jaw pain and stiffness levels after repeated maximum voluntary clenching.

Ten normal male volunteers performed six maximum voluntary isometric jaw-closing muscle contractions within an 80-minute experimental period. Each individual contraction was sustained until maximum pain tolerance was reached. Before and one, two, three, and seven days after the experiment, the following measures were made: (1) superficial masseter and anterior temporalis muscle tenderness (pain threshold), (2) jaw movement (opening and lateral excursion), and (3) current pain level for the right and left sides of the jaw. In this study, measures of current jaw pain, muscle pain threshold, maximum active opening, and maximum lateral excursions showed no significant post-experimental changes. These results challenge the idea that sustained isometric clenching in healthy male subjects could be used as a model for chronic or even subacute muscle pain, as has been suggested by previous investigators.

Adult↗
PubMed1993

Co-activation of sternocleidomastoid muscles during maximum clenching.

In an attempt to determine the degree of co-activation present in selected cervical muscles during clenching, we instructed 12 male subjects to produce four brief maximum voluntary contraction (MVC) efforts (clenching) in a position of maximum intercuspation. Surface EMG activity was recorded bilaterally from the masseter and sternocleidomastoid (SCM) muscles. The contraction level for the SCM during clenching was reported as a percentage of the SCM's maximum activity achieved during maximum neck flexion against resistance. All EMG signals for the masseter and SCM were converted to a true RMS voltage signal and digitized at a 100-Hz sampling rate. Mean peak EMG voltage levels were determined for the activity recorded during each brief MVC task. All subjects demonstrated co-activation of the SCM during strong abrupt clenching efforts. The mean levels (+/- S.D.) of SCM activity were 11.8 +/- 9.6% (right) and 14.2 +/- 9.4% (left) of the MVC capacity. Fifty percent of masseter activity was required to achieve 5% activity of the SCM bilaterally, and there was a progressive development of the SCM co-activation which paralleled the masseter activation.

Adult↗