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The clinical, radiological, and electrophysiological data of a 25-year-old woman with "inverse masticatory muscle activity" due to syringobulbia is presented. This uncommon brain stem syndrome may be due to a disturbance in central programming of mastication.
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The orientation of these lines of action was estimated in 9 healthy subjects, by reconstructing the muscle shape from a series of parallel sections obtained by MRI. In order to gain insight into sources of error, the lines of action of the masseter and medial pterygoid were estimated from two mutually perpendicular series of sectional images. Average results were compared with anatomical data from the literature. The results indicated that the accuracy of the estimate was principally dependent on the reliability of the reconstructions; the average accuracy of the estimated orientations was about 5 degrees.
Rhythmic jaw movements were observed in lightly anesthetized rats when a bitable object was placed between the maxillary and mandibular incisors. To elicit the jaw movements, an initiating stimulus was required. A successful stimulus was to push on the mandible at the incisors in both opening and posterior directions. This may be a suitable movement for studying mastication because of the following properties: (i) The rhythmic jaw movements could not continue without tooth contact. (ii) The timing pattern of the electromyographic activity of the masseter and digastric muscles and the tooth contact was similar to that of human mastication. (iii) Frequency of the movements was independent of hardness of the object placed between the incisors, though oral stimulation easily stopped the movement as did a noxious stimulus applied around the oral cavity. We conclude that peripheral activation, which may be generated by tooth contact, is as essential to the rhythmic jaw movement as central activation.
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The activity of the temporal and masseter muscles and of the upper lip was examined by electromyography in five adults and in five children who had sustained uni- and bilateral fractures of the mandibular condyle. Electromyographic recordings were done in the postural position of the mandible, during maximal bite in the intercuspal and retruded mandibular positions, during chewing and swallowing of peanuts and during swallowing of water. In the children, who were examined on three occasions after the trauma, a reduced muscle activity was found shortly after the trauma, but it had normalized at follow-up examination 1 year after the injury. The adults, who were examined 4-6 years after the trauma, had, in general, normal muscle function. In subjects with a unilateral fracture, no difference in muscle activity was found between the two sides. An enlarged distance between the retruded and intercuspal positions of the mandible did not, in these subjects, seem to influence the muscle activity during the functions studied.
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Surface electromyography was used to study the function of the anterior temporal, surface masseter, deep masseter and anterior digastric muscles of 14 patients after complete rehabilitation of occlusion with fixed prostheses and/or removable partial prostheses. All patients had a balanced occlusion with protection by non-working side contacts during lateral excursion. Mean resting myoelectric activity was 2.5-3.8 microV, showing no hypertonia or muscular spasm. When patients clenched their teeth (i.e. exerted maximum voluntary occlusal force in centric occlusion), the anterior temporal muscles were the most active, followed by the surface masseters; the digastrics were significantly less active. During lateral displacements, the muscles exhibiting significantly higher potentials than the other muscles monitored were the working side anterior temporal muscle and the contralateral surface masseter. During mastication, the muscle that was most active in relation to its contralateral homologue was the working side surface masseter, the difference between the two being statistically significant.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
The purpose of this study was to analyze the control mechanism of quiet period (silent period, QP) in myoelectric signals of the masseter and the anterior part of temporalis by the measure of frequency analysis (FFT) and the power spectra, according to the bite force developement. Surface myoelectric signals of te masseter and the temporalis (both sides) of nine human subjects with normal occlusion were recorded during biting movements. Subjects were asked to increase their forces rapidly to their maximum bite force levels at the decided three rate (0.5sec, 1.0sec and 2.0sec) respectively. QPs (duration; 10 approximately 70ms) were observed (occurrence rate; 44%) almost simultaneously in four muscles at both experimental conditions of the high accelerative movements (0.5sec) and of low levels of bite force remarkably. Frequency analyses were carried out by means of Fast Fourier Transform about myoelectric signals for the period of each 50ms before and after QP occurrence. In the higher frequency bands (200 approximately 480Hz), power spectra "AFTER QP" were distributed with high energy density, whereas "BEFORE QP" were characterized in low frequency bands (20 approximately 180Hz) with low energy. By these analysis, following results were discussed such as that the recruitment of phasic motor units (high frequency bands of power spectra) appeared with fast rate coding in the EMG of QP occurrence, and it should be natural for the neural switching mechanism to be activated in QP occurrence in order to transfer from tonic units to phasic ones of EMG.
Temporomandibular disorders (TMD) are characterized by several signs and symptoms, such as pain and changes in the electrical activity of masticatory muscles. Considering that transcutaneous electrical nerve stimulation (TENS) is a resource indicated to promote analgesia, the objective of this study was to evaluate the effect of TENS on pain and electromyographic (EMG) activity of the jaw elevator muscles in TMD patients. This study evaluated 35 female volunteers: 19 TMD patients (mean age = 23.04 +/- 3.5) and 16 normal subjects (mean age = 23.3 +/- 3.0). Transcutaneous electrical nerve stimulation (conventional mode, 150 Hz) was applied once to each group for 45 minutes. Surface electromyography (gain of 100 times and 1 kHz sampling frequency) and the visual analogue scale (VAS) were applied before and immediately after TENS application. Both VAS data and root mean square (RMS) values were analyzed using Student's t-test. The TMD group, compared to the control group, showed higher EMG activity of the jaw elevator muscles at rest. No difference was observed between the groups regarding maximum voluntary clenching (MVC). In TMD patients, TENS reduced both pain and EMG activity of the anterior portion of the temporal muscle, increasing the activity of the masseter muscles during MVC. It is possible to conclude that a single TENS application is effective in pain reduction. However, it does not act homogeneously on the features of the electric activity of the muscles evaluated.
The purpose of this study was to evaluate the effect of stabilization splint therapy on occlusal force in patients with masticatory muscle disorders (MD). Six female patients with myalgia or myofascial pain participated in this study. The occlusal points and load on the dental arch in maximum clenching was measured using the computerized system with Dental Prescale(R) before and after the use of the splint. There were no significant changes in the number of occlusal points, mean occlusal pressure, and asymmetry in occlusal balance between before and after the use of the splint. However, there were significant differences in the extent of the area of occlusion and in the integrated occlusal loads. The integrated occlusal load converged to the normal level with the use of the splint. From the results of this study, it is suggested that the use of the stabilization splint has the effect of normalizing the occlusal force.
The influence of the experimental occlusal discrepancy on masticatory muscle activity was investigated on 12 subjects. Specially designed occlusal interferences were fabricated and various occlusal states were simulated with their aid. Subjects were asked to carry out eccentric clenching efforts and electromyographic activity of the masseter plus the anterior and posterior temporal muscles was measured. When compared with clenching on the unaltered natural dentition, clenching on the experimental interferences resulted in distinct patterns in the jaw elevator muscles, and the most characteristic change was observed when clenching effort was exerted on the experimental non-working side interference. Electromyographic activity in the anterior and posterior temporal muscles was decreased on the working side and increased on the non-working side and originally unilateral activity pattern with clear dominance on the working side was altered to a bilateral pattern, while that of the masseter muscles remained uninfluenced. Resultant bilateral activity in the anterior and posterior temporal muscles is thought to cause a superior movement of the working side condyle and an inferior movement of the non-working side condyle.