[Electromyographic study on the pattern of masticatory muscle activity following correction of reversed occlusion].
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Effect of canine guidance of maxillary occlusal splint on level of activation of masticatory muscles.
The effect of canine guidance of a full-arch maxillary flat occlusal splint on the level of activation of the anterior and posterior, temporal, masseter and suprahyoid muscles during maximal clenching, were studied in 14 subjects without craniomandibular disorders. The results revealed that, the level of electromyographic activity of anterior and posterior temporal and suprahyoid muscles during maximal clenching on the occlusal splint in habitual closure was unchanged, as compared to biting in the intercuspal position (ICP), while the activity in the masseter muscle, on average, was increased slightly (13 percent). In contrast, the level of activation of the jaw elevator muscles decreased significantly during maximal clenching on the cuspid ramp of the splint, as compared to the biting in ICP or clenching on the splint. However, the degree of reduction of activity was not symmetrical, and was most pronounced in the masseter muscle of the biting side and in the anterior and posterior temporal muscles of the non-biting side. No significant difference was observed in the activity of the suprahyoid muscles.
Adult↗
Overall activity of all masticatory muscles during lateral excursion.
Quantification of the overall activity of every masticatory muscle is requisite for the analysis of stomatognathic function, which has not been accomplished by conventional electromyography. We used positron emission tomography and 18F-fluoro-deoxy-glucose to quantify the overall activity of every masticatory muscle during lateral excursion, and to evaluate the relative contribution of each masticatory muscle to lateral excursion. The present study suggested that lateral and medial pterygoid muscles are more responsible for lateral excursion than are masseter and temporal muscles. In particular, the contralateral lateral pterygoid muscle plays a major role, followed by the contralateral medial pterygoid muscle.
Adult↗
Differentiation of histochemical properties of masticatory muscles in Bovidae and Cervidae (Artiodactyla).
We analyzed the masticatory muscles (masseter, temporal, medial pterygoid and lateral pterygoid muscles) of Bovidae and Cervidae (Artiodactyla) for the histochemical characteristics of their fiber types. Analysis of muscle fiber types in the present study was based on the staining reaction for SDH, Sudan black B, alpha-GPDH, and myosin-ATPase after alkaline preincubations. Histochemical properties were found to contribute to masticatory function, including a slow-twitch fatigue resistant activity derived from the high percentage of red fibers, in spite of the differences in the distributions of fiber types in three portions (superficial, medial and profound portions) of each masticatory muscle. These results indicate a correlation between the histochemical profiles of individual masticatory muscles in these species and their functions during jaw movements.
Animals↗
[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↗
Masticatory muscle influence on craniofacial growth.
The influence of the masticatory muscle function on craniofacial growth has been recorded in a series of animal experimental and clinical studies. The common characteristic of these investigations is that the elevator muscles of the mandible influence the transversal and the vertical dimensions of the face. The increased loading of the jaws due to masticatory muscle hyperfunction may lead to increased sutural growth and bone apposition, resulting in turn in an increased transversal growth of the maxilla and broader bone bases for the dental arches. Furthermore, an increase in the function of the masticatory muscles is associated with anterior growth rotation pattern of the mandible and with well-developed angular, coronoid, and condylar processes.
Animals↗
Temporomandibular joint and masticatory muscle involvement in myotonic dystrophy: a study by magnetic resonance imaging.
OBJECTIVE: The purpose of this study was to evaluate the masticatory muscles and the temporomandibular joint (TMJ) by magnetic resonance imaging (MRI) in myotonic dystrophy (MD) patients. STUDY DESIGN: MRI of the masticatory muscles and TMJ was performed in 15 MD patients, 11 male and 4 female, aged 16 to 53 years (mean, 31 years). Many of them had dental malocclusion, especially Angle class III and anterior open bite, and 3 complained of recurrent TMJ dislocation. TMJ and masticatory muscle pain was not observed, and joint sounds were noted in only 1 patient. RESULTS: The analysis of MRI scans showed masticatory muscle involvement in 13 patients (86.6%). In 11, the involvement was moderate to intense. The main abnormalities observed were increased intramuscular tissue signal on T1 (fatty infiltration) and volumetric reduction of muscles. Regarding the TMJ, articular disk displacement was seen in only 1 patient, but abnormalities of disk shape were common. Mild bone abnormalities were frequently observed, including changes of shape and contour of bone surface, and sclerosis of bone marrow. In 4 patients the condyle moved anterior to the eminence with the mouth opened fully (condylar hyperexcursion). CONCLUSIONS: This study shows that masticatory muscles are frequently and intensively affected in MD patients. Bone changes are the most consistent abnormalities observed in the TMJ. It is possible that remodeling is caused by biomechanical changes in the jaw as a result of masticatory muscle involvement.
Adipose Tissue↗
Distribution of the macromolecular components of masticatory muscles during differentiation of the muscle fibers in the postnatal rat.
The distribution of collagen fibers of rat masticatory muscles during the postnatal period (two weeks), was investigated by electrophoresis and immunohistochemistry. At these stages, the myosin of rat masticatory muscles displays specific electrophoretic patterns. Comparison of the myosin patterns of these muscles allows their identification. 1) Analysis by SDS-PAGE indicated that one of three weakly reactive stainable proteins with lower mobility than the heavy chain of myosin disappeared from the temporal muscle on day 13, as compared with other masticatory muscles. However, in histochemical analysis of the muscle fibers, the reaction specific for succinic dehydrogenase (SDH) activity was strong, and the fibers on day 13 could be classified into two types with respect to SDH activity. By contrast, on day 0, the fibers were classified into two types with respect to myosin ATPase activity. 2) Immunohistochemical analysis indicated that the distribution of the components of the extracellular matrix in the epimysium (type I collagen), perimysium (type I collagen, fibronectin, and laminin) and endomysium (type III collagen, fibronectin, laminin, and tenascin) was related to the metabolic capacity on days 12 to 13. The variability in the types of myosin and in proteins of the extracellular matrix might be important during the development of rat masticatory muscles.
Animals↗
Growth and allometry in primate masticatory muscles.
A study of the dry weight of primate and non-primate masticatory musculature permitted possible allometric and ontogenetic influences on this musculature to be explored. Using weight as an indicator of adult body size, all of the masticatory muscles examined (anterior temporalis, posterior temporalis, masseter, medial pterygoid, lateral pterygoid, digastrics, and total adductor mass) are isometric. This is true even when prosimians and non-primates are removed from consideration, leaving only adult anthropoid primates. Thus, size-related changes do not affect the masticatory musculature of anthropoids differently from the musculature of examined prosimians and non-primates. However, other measures of body size (skull length, head and body length) reveal a different picture. Yet, irrespective of the indicator of body size chosen, the allometric properties of the masticatory muscles appear similar and the fluctuations of the various muscle indices therefore reflect functional changes, and are not caused by allometry. Exudate-eating and frugivory are discussed in relation to body size and the development of the mandibular depressor muscles. The logs of the masticatory muscles do not show a significant correlation with age, except when species are followed across age grades. For the five anthropoid species for which this is possible, the medial and lateral pterygoid and digastric muscles are still not correlated with age. When all examined species are considered, some muscle ratios correlate significantly with age. Following anthropoid species across age grades singles out an early surge in growth of the medial pterygoid muscle over the masseter muscle, a situation which was apparent also in the general age correlation.
Age Factors↗
[Morphometric and histochemical studies of the masticatory muscles in growing white rats following ligation of the right common carotid artery].
White Wistar rats served for examinations to the masticatory muscles after ligature of the a. carotis communis dextra on the 42nd d after birth. Gravimetric determinations of the dry substance of the muscles were performed in a total of 229 animals. In 65 animals casts of the vessels in synthetic resin (Kallocryl M) were made and the inside diameters of the blood vessels of the corresponding vascular regions measured. Histological, histochemical and muscle-fibre-morphometric observations of the masticatory muscles were made in 10 animals. Due to processes of adaption the a. carotis communis sinistra with an enlarged cross-section supplied the head with an increased blood volume. However, the anatomical and physiologic conditions of the collateral blood vessels conveying blood to the right side of the head prevented the entry of same share of blood into that side. Obviously there is a causal connection between this circumstance and the reduction in the dry substance of the right-side masticatory muscles. Histologic investigations revealed an increase in the capillaries by 10 percent in the animals operated on. The reduction in the diameters of the muscle fibres on the right side of the head was accompanied by a change in the normal combination of fibre types. 2 out of 5 animals which had been operated on showed a fairly homogeneous distribution of the fibre types in the masticatory muscles. Fibres of type 2 tended to be more vulnerable than fibres of type 1. Pathogenetically, the reduction in the dry substance of muscles and the reduction in the diameters of the muscle fibres are caused by nutritive disturbances in connection with restricted circulation. The neuronal-trophic sphere and the mechanism which is responsible for the differentiation of the muscle-fibre types seem to be affected as well. The myokinetic synapses are not affected.
Aging↗
Morphological classification of the masticatory muscles in dogs based on their innervation.
The masticatory muscles and their innervations in dogs are classified, from deep to superficial layers, as follows: 1) medial pterygoid muscle and medial pterygoid nerve, 2) lateral pterygoid muscle and lateral pterygoid nerve, 3) anterior deep part of temporal muscle and anterior deep temporal nerve, 4) posterior deep part of temporal muscle and posterior deep temporal nerve, 5) superficial part of temporal muscle and superficial temporal nerve, the only branch of the temporal nerve which passes out from the infratemporal fossa, 6) zygomaticomandibular part of masseter muscle, which is thought to belong to the masseter muscle, and masseter nerve, 7) deep layer of masseter muscle and masseter nerve, 8) superficial layer of masseter muscle and masseter nerve.
Animals↗
Growth patterns of the rabbit masticatory muscles.
The post-natal growth of the masticatory muscles in the rabbit was examined. By means of anatomical dissection and measurement, total muscle length, muscle fiber length, and muscle weight were determined in animals varying in age between one week and 36 months and exhibiting a 50-fold weight increase. Growth data were fitted by linear regression models with facial skull length used as the independent variable. Many deviations occur from size-dependent isometric growth. The muscles can be divided into three groups, according to their pattern of weight increase: The jaw openers grow negatively allometrically, and their contribution to total muscle weight decreases with time; the temporal muscle grows negatively allometrically, but its relative weight proportion remains about the same; the masseter and medial pterygoid muscles have positively allometric growth, and their contribution to total muscle weight increases strongly. Generally, the length of the muscles and of their fibers increases at lower rates than does the length of the facial skull. After weaning, the rate of longitudinal growth drops steeply in some muscles. Total fiber area or physiological cross-section (PCS) of muscles is computed from weight and fiber length. It increases positively allometrically in the jaw closers and negatively allometrically in the jaw openers. In the lateral pterygoid muscle, the increase of PCS changes from negatively- to positively-allometric growth after weaning. The study demonstrates that individual oral muscles follow different patterns of longitudinal and cross-sectional growth, so that their functional capacities (force, range of contraction) and mutual functional relationships are age-dependent.
Animals↗
[Functional morphology of the maxillo-mandibular apparatus in the miniature swine MINI-LEWE. 8. The development of the intramuscular nerve ramification pattern in the masticatory muscles].
Postnatal changes in the intramuscular innervation pattern of the masticatory muscles of the miniature pig MINI-LEWE are only gradual. There are no definite relationships between the paths of nerves and the positions of the fasciae. The few anastomoses found were in the masseter muscle. The only other nerve found to be implicated in the motor innervation of the masticatory muscles was the motor root of the trigeminal nerve. Innervation studies are a good way of identifying the bounds of muscles: the masseter and zygomaticomandibularis muscles, for instance, are innervated jointly by the massetericus nerve, so that the zygomaticomandibularis muscle can be regarded as belonging to the masseter muscle.
Animals↗
A randomized clinical trial of intraoral soft splints and palliative treatment for masticatory muscle pain.
Thirty subjects seeking treatment for masticatory muscle pain at a university-based TMJ clinic were randomly assigned to soft-splint, palliative-treatment, and no-treatment groups. After 4 to 11 weeks of treatment, subjects were evaluated for changes from their baseline levels of symptoms, maximum pain-free opening, pain thresholds measured by a pressure algometer, and occlusal contacts. With the use of the multivariate analysis of variance and analysis of covariance, the results suggest that the soft-splint group had statistically significant improvement (P < .01), the palliative-treatment group had improvement that was not statistically significant, and the no-treatment group had a slight aggravation of symptoms. The soft-splint group had fewer occlusal contact changes assessed with shimstock compared to the palliative-treatment and no-treatment groups. The findings of this study suggest that the soft splint is an effective short-term treatment for reducing the signs and symptoms of masticatory muscle pain in patients, and the soft splint does not cause occlusal changes.
Adolescent↗
Experimental masticatory muscle pain.
Ten female subjects with no history of temporomandibular disorders performed five exercises designed to induce masticatory muscle pain. Three of the exercises were replications of Christensen's tooth-clenching (1970) and tooth-grinding (1971) studies and Scott and Lundeen's mandibular protrusion (1980) study. The other two exercises were designed to induce specific unilateral masticatory muscle pain. The amount of muscle pain as well as the time of onset and the duration were assessed by a clinical palpation exam and a pain questionnaire. These five pain-inducing methods did not consistently produce masticatory muscle pain in non-pain subjects. However, certain individuals appeared to be very susceptible to developing pain during or after most of the exercises. These susceptible individuals demonstrated a bilateral muscle pain pattern after the unilaterally stressful exercises. None of the five exercises produced a statistically significant amount of site-specific masticatory muscle pain as determined by either the palpation examination or the pain questionnaire, even when the exercise was intended to produce such specificity. The fact that some subjects did develop masticatory muscle pain is indicative that muscle exercise and fatigue may lead to TMD-like symptoms.
Adolescent↗
Quantitative analysis of masticatory muscles using computed tomography.
Quantitative information on the normal size range of the masticatory muscles needed for successful treatment of facial asymmetry is sparse. Our purpose in this study was to define morphological indicators for the volume of the masticatory muscles on CT. Cross-sectional areas and volumes of the masseter and medial pterygoid muscles were measured from CT scans of 65 patients. The muscles were scanned from origin to insertion and the maximum cross-sectional area (MCSA) and its location together with the total volume were determined. The mandibular foramen was used as a landmark to determine the location of MCSA. The location of MCSA of masseter muscle was centred 8 mm above the mandibular foramen, and that of medial pterygoid muscle at the foramen. The MCSA of both muscles was highly correlated with volume suggesting that this parameter might serve as an indicator of their volume. Knowledge of the location of the MCSA would facilitate its measurement and so reduce radiation exposure. There was a positive correlation between the two muscles for both volume and MCSA. This finding could be relevant for future studies of the relationship between the morphology, biomechanics and pathology of the masticatory muscles.
Adult↗
Developmental changes in enzyme activities and in structural features of rat masticatory muscle mitochondria.
The functional ability of a muscle is closely related to the activities of the mitochondria, which are energy-producing organelles in muscle cells. The development of the mammalian masticatory muscle progresses dramatically when feeding behavior changes from suckling to mastication, but it is unclear how the energy-producing systems of the mitochondria change. In this paper, the development of rat masticatory muscle mitochondria was investigated in terms of enzyme activities of the mitochondrial respiratory chain and the structural and numerical development of mitochondria, especially regarding the change in feeding behavior from suckling to mastication. Using isolated mitochondria from the masticatory muscle, we measured succinate dehydrogenase, NADH dehydrogenase, succinate-O2 oxidoreductase, and NADH-O2 oxidoreductase. These were found to be increased in the 15-day postnatal rat compared with the 0- to 10-day postnatal rat. The structural development of mitochondria was gradual in the 0- to 15-day postnatal rat. However, a notable increase was found in the cross-sectional area of mitochondria between 10 and 15 days postnatally. The number of mitochondria per muscle fiber was apparently constant during the same period. We demonstrated that the change in feeding behavior was well-correlated with an increase in mitochondrial enzyme activity, also supported by the early structural development of mitochondria.
Aging↗
Power spectral analysis of electromyographic signal of masticatory muscles at rest position and habitual clench.
Thirteen normal subjects were selected for this investigation. At the vertical dimension of rest position and habitual clench, their myoelectric activities of the masseter, anterior and posterior temporal, and digastric muscles on the left and right sides were simultaneously sampled and processed by computer, and the mean power frequency (MPF) and the mean amplitude (MA) of the myoelectric signal were calculated. At rest position, the temporal muscles were major muscles and the MPF differences of various masticatory muscles were not significant. At habitual clench, with the increase in MA, the MPF of various muscles increased. The results show that MPF may have application in describing a central tendency of myoelectrical signal frequency distribution and in evaluating recruitment of motor units. MPF and MA are the quantitative indices reflecting masticatory muscle function.
Adult↗