[Behaviour study on masticatory muscles by electromyography--Muscular fatigue and chewing rhythm of masticatory muscles (author's transl)].
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Electromyography↗
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Analysis of the tendinous structure in human masticatory muscles.
In the masticatory muscles, the development of bundles of the tendon was examined: they were composed of many collagen fibers and a few elastic fibers. In the masseter muscle, the property of the tendon differs in the distribution and size of collagen fibers and elastic fibers in comparison with those of other masticatory muscles. This difference is concerned with the kinetic force for the stress or the stretch of each tendon and muscle during jaw movement.
Aged↗
Muscle spindle supply to the masticatory muscles in the Japane ermine (Carnivora).
Histological examination of the jaw muscles of the Japanese ermine showed that 4 jaw-closing muscles have 13 muscle spindles on one side of the face. The temporal muscle has 99 muscle spindles, 68 being in the anterior vertical and 31 in the posterior horizontal belly. The masseter muscle has 33 muscle spindles, 23 being in the profound and 10 in the superficial belly. The medial pterygoid muscle has 7 muscle spindles and the zygomaticomandibular muscle contains 4 muscle spindles. The lateral pterygoid and the jaw-opening muscles have no spindles.
Animals↗
Myosin isoform transitions during development of extra-ocular and masticatory muscles in the fetal rat.
The late fetal development of rat extra-ocular and masticatory muscles was examined by myosin immunohistochemistry. The pattern of slow and neonatal myosin isoform expression in primary and secondary myotubes in these muscles was generally similar to that seen by others in limb muscles. We observed a consistent difference between the Sprague-Dawley and Wistar rats in the degree of maturity reached by all muscles studied at a particular age. In both strains, extra-ocular muscles were also about one day in advance of the masticatory muscles. Thus, secondary myotubes were first seen at E17 in Wistar extraocular muscles, at E18 in Sprague-Dawley extra-ocular muscles and Wistar masticatory muscles, and at E19 in Sprague-Dawley masticatory muscles. There was a strikingly early and complete type differentiation of primary myotubes in extraocular muscles, and tonic myosin first appeared before birth in presumptive extrafusal tonic fibres in the orbital layer of the oculorotatory muscles. Throughout the late fetal period, retractor bulbi was composed of fast myotubes only, but these myotubes were not arranged in classical clusters. In the masticatory muscles at E17/E18 some slow primary myotubes started to express tonic myosin, and these presumptive spindle bag2 fibres were located only in regions of the muscles known to contain spindles in the adult. Presumptive bag1 fibres appeared about a day later (initially without tonic myosin), and in the region of the spindle cluster in anterior deep masseter extrafusal secondary myotube production appeared to be suppressed.
Animals↗
[Evaluation of a histochemical method specific for myosin ATPase activity in the masticatory muscles of the rat].
A biological study of masticatory muscle behaviour (Divry and Westphal, 1991) suggested the analysis of physiologic correlates (biologic parameters related to a behavioural event) such as histochemical reactions of muscular fibres studied by M-ATPase and SDH activities. For such investigations, routine methods are needed. In the present study, a modification of the original method of Tunell and Hart (1977) was used, in which three features of the original alkaline preincubation method (composition, incubation time and pH) were modified. These allowed a single step differentiation of the various fibre types found in rat masticatory muscles, for which the classical technics gave only a weak contrast, not suitable for image analysis. Acid preincubation was also tested but failed to give new information. By combining this modified technic with SDH staining (Nachlas, 1957) a classification of fibres into 12 theoretical types was proposed.
Alkalies↗
Evidence that the masticatory muscles receive a direct innervation from cell group k in the rabbit.
These experiments have shown that a group of neurons lateral to the trigeminal motor nucleus innervates the muscles of mastication. The work began to describe the location of digastric last-order interneurons, using the technique of transneuronal labeling with wheatgerm agglutinin-conjugated horseradish peroxide injected into the left digastric muscle of rabbits under general anaesthesia. Four to eight days later, the animals were killed with an overdose of anaesthetic and perfused. Coronal sections of the frozen brainstem were cut at 20 microns thickness and processed for peroxidase activity. Motoneurons in the ventral and caudal divisions of the trigeminal motor nucleus were labeled in all animals as expected. An additional population of neurons located ventrolaterally to the motor nucleus in cell group k were also found to be labeled if the survival time was five days or more. In an attempt to determine whether cell group k neurons were labeled transynaptically, two series of control experiments were carried out. In the first, crystals of fluorescein- and rhodamine-conjugated dextran amines and horseradish peroxidase were applied directly to central ends of cut digastric nerves. In the second, central ends of cut digastric nerves were enclosed in cuffs containing 40-60% horseradish peroxidase solutions. Again, neurons in both the trigeminal motor nucleus and cell group k were labeled suggesting that neurons within cell group k project to the digastric muscle. Similar experiments using dextran amines and wheatgerm peroxidase were carried out on the masseter muscle. Motoneurons in the dorsomedial and rostral half of the trigeminal motor nucleus, as well as primary afferent cell bodies in the mesencephalic nucleus of the trigeminal nerve, were labeled in all experiments. In addition, a population of neurons in cell group k, dorsal to those associated with the digastric muscle, were found to contain each one of the reaction products. Since it is thought that only the wheatgerm agglutinin-conjugated horseradish peroxidase transferred from one neuron to another, we conclude that cell group k neurons provide an additional innervation to the digastric and masseter muscles.
Animals↗
[Structural analysis of the masticatory muscles].
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Fascia↗
[Role of functional interaction between the facial and masticatory muscles in the genesis of synkineses in patients with neuritis of the facial nerve].
The electromyogram of orbicular muscles of the eye and masticatory muscles was studied in 19 patients with facial nerve neuritis and 11 normals. In a maximum contraction of the masticatory muscles, the orbicular muscles of the eye showed an activity equal to about 9% of the maximum amplitude of the orbicular muscles. Similar activity in the paretic muscles was not decreased. The development of secondary synkinesia is postulated.
Adolescent↗
Dental treatment of temporomandibular disorders and masticatory muscle pain.
The treatment of masticatory muscle and temporomandibular joint pain constitutes an important area in dentistry. Current information supports the use of reversible treatments for these disorders. Several recent references are discussed in relation to reversible treatment, the role of occlusion, and appliance therapy for internal derangement.
Facial Pain↗
Demonstration of 'cardiac-specific' myosin heavy chain in masticatory muscles of human and rabbit.
Human and rabbit masticatory muscles were analyzed immuno- and enzyme-histochemically using antibodies specific to 'cardiac' alpha, slow and fast myosin heavy chain isoforms. In human masseter, temporalis, and lateral pterygoid muscle 'cardiac' alpha myosin heavy chain is found in fibres that contain either fast, or fast and slow myosin heavy chain. In rabbit masseter, temporalis and digastric muscles, fibres are present that express 'cardiac' alpha myosin heavy chain either exclusively, or concomitantly with slow myosin heavy chain or fast myosin heavy chain. Our results demonstrate a much broader distribution of 'cardiac' alpha myosin heavy chain than hitherto recognized and these might explain in part the specific characteristics of masticatory muscles. The 'cardiac' alpha myosin heavy chain is only found in skeletal muscles originating from the cranial part of the embryo (including the heart muscle), suggesting that its expression might be determined by the developmental history of these muscles.
Adult↗
[A functional assessment of the masticatory muscles in mammals and humans].
We have amended and added to Fabian's tables giving a functional assessment of individual masticatory muscles. The data in our tables refer only to the temporalis, masseter, pterygoideus medialis, pterygoideus lateralis and digastricus muscles. The weights of these muscles were determined in three fixed human cadavers and the mean values compared with those of apes, carnivores, herbivores and rodents. In humans, the most powerful masticatory muscle is the M. temporalis, followed by the M. massater, as in apes and carnivores. The M. pterygoideus is also one of the most important. This is remarkable, since in the other groups this muscle occupies the last place. This relative strengthening of the M. pterygoideus lateralis is an important characteristic of the human masticatory apparatus. In humans, the difference between the relative weights of the individual masticatory muscles is not nearly so great as in other mammalian groups. The M. pterygoideus lateralis does lie close behind the other two big adductors (Mm temporalis and masseter) but, as regards power and weight, it hardly differs from the M. pterygoideus medialis and the M. digastricus. In humans the strengthening affects not only the M. pterygoideus lateralis but also the M. digastricus. It would seem that these two masticatory muscles could become the key to the understanding of the specific changes in human mastication.
Animals↗
Craniomandibular disorders and masticatory muscle function.
The heading craniomandibular disorders covers a wide range of abnormal and pathologic conditions accompanied by orofacial pain and impaired mandibular function, the masticatory muscles and the temporomandibular joints being the structures most frequently involved. Prevalences of severe craniomandibular disorders accompanied by headache and facial pain urgently in need of treatment are 1-2% in children, about 5% in adolescents, and 5-15% in adults, with higher values in women than in men. With respect to physiology and ergonomics, masticatory muscles are comparable to other human skeletal muscles, e.g. of shoulder, neck and lower back. Therefore these muscles share pathogenesis, symptoms and signs of muscular disorders caused by prolonged, low-level static contractions or intermittent isometric contractions at higher levels. Since the same elements of performance in the masticatory muscles are influenced by occlusal factors, they link the development of muscular fatigue, discomfort and pain to the dental occlusion. Furthermore, changes of the occlusal surfaces, e.g. due to dental treatment, may influence the performance of the masticatory muscles, and consequently interfere with local muscular function.
Adolescent↗
Proprioceptive innervation of the masticatory muscles in Pinché.
This study of the masticatory muscles of the primate showed that the temporal muscle contained 107 muscle spindles, 45 in the horizontal portion and 62 in the vertical portion; the masseter muscle contained 70, 58 in the profundus portion and 12 in the superficial portion; the medial pterygoid muscle contained 15; the lateral pterygoid muscle contained 6; and the zygomaticomandibular muscle contained 9. The muscle spindles were located around the coronoid process and mandibular ramus.
Animals↗
Motor nuclear representation of masticatory muscles in the rat.
Representation of the masticatory muscles within the motor trigeminal nucleus was studied in rats by the horseradish peroxidase (HRP) method and the antidromic field potential method. The motor trigeminal nucleus of the rat could be divided cytoarchitecturally into a dorsolateral and a ventromedial division. Within the dorsolateral division, the temporal muscle was represented dorsomedially, the masseter muscle dorsolaterally and laterally, and the lateral and medial pterygoid muscles ventrolaterally. Within the ventromedial division, the anterior digastric muscle was represented dorsomedially and the mylohyoid muscle ventrolaterally. Distribution of antidromic field potentials evoked by stimulation of the mylohyoid and masseteric nerves coincided with the results from the HRP investigation.
Animals↗
[A method for performing stimulation electromyography of the masticatory muscles in man].
A principal block scheme of an apparatus complex is suggested and a method for examination of masticatory muscle function is described. The method is based on electrostimulation of masticatory nerve followed by registration and analysis of the masticatory muscle action evoked potentials. The block scheme of the apparatus complex includes a universal electrostimulator ESU-2. Examinations of 30 healthy volunteers and 30 patients with unilateral fractures of the mandible helped define the major parameters of stimulation electromyography. The patients were treated by splints applied on the teeth with fixation on both jaws. By day 28 of the investigation the M-response amplitude dropped more than twofold and its length by 1.5 times as against the mean parameters in health.
Action Potentials↗
Malocclusion and masticatory muscle activity: a comparison of four types of malocclusion.
Electromyographic activities of the temporalis and masseter muscles during mastication were measured in patients who visited this clinic for orthodontic treatment of progenia. The results obtained were compared with those previously obtained in patients with other types of malocclusion and relationships between types of malocclusion and activities of the masticatory muscles were examined. Several interesting results were obtained, including: 1) the muscle activities were significantly higher in patients with deep bite than in patients with any other types of malocclusion and 2) inefficient mastication patterns, evidenced by higher temporalis muscle activities on the balancing side than on the working side, were most frequently observed in patients with edge bite. These results indicate that the clinical evaluation of masticatory muscle activities may be useful in improving orthodontic treatment and in determining a proper retention period after the treatment. The results also suggest that orthodontic treatment should include some type of dynamic myofunctional therapy in addition to the correction of static structural abnormalities.
Child↗
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↗
Horseradish peroxidase localization of masticatory muscle motoneurons in cat.
Horseradish peroxidase has been injected into individual masticatory muscles in young and adult cats in order to determine the topography of the corresponding groups of motoneurons in the motor nucleus of the Vth nerve. The results obtained show a clear dorsoventral somatotopic distribution; the superior muscles have their motoneurons located dorsally in the nucleus and the inferior muscles ventrally; the two main jaw closers, temporalis and masseter, are represented in the dorsal and central parts of the nucleus; located more ventrally are the motoneurons for the pterygoideus medialis and lateralis, the jaw closers and abductor muscles; finally motoneurons for the jaw openers, and the anterior belly of the digastricus and mylohyoideus, occupy the ventromedial part of the nucleus. All muscles have been found to be represented along the entire length of the nucleus, with the same dorsoventral layering.
Animals↗