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PubMed1999

Characteristics of the muscle spindle endings of the masticatory muscles in the rabbit under halothane anesthesia.

To explore the response characteristics of muscle spindle units in the masticatory muscles in the rabbit, the responses of muscle spindle units were recorded from the mesencephalic trigeminal nucleus (MesV) under halothane anesthesia during ramp-and-hold stretches. Three firing patterns, initial burst (IB) at the onset of the dynamic phase, negative adaptation (NA) at the end of the dynamic phase and firing during the release (FDR) phase, were observed during muscle stretch. IB was present at higher stretch velocities, FDR at lower stretch velocities. The velocity at which an IB or FDR was present was different from unit to unit. Because, within the range of the velocities of stretch tested, units with NA always showed NA and units without NA never did, all recorded units were divided into two groups on the basis of the existence of NA (NA(+) or NA(-) units). Response characteristics of the two groups were then compared. NA(+) units showed an IB more frequently and FDR less frequently than NA(-) units. NA(+) units had significantly higher dynamic responsiveness and discharge variability than NA(-) units. The conduction velocity of the afferents of NA(+) units was higher than that of NA(-) units. However, distributions of these measurements were not bimodal. These results suggest that NA is the useful criteria to classify the muscle spindle endings in the masticatory muscles in the rabbit under halothane anesthesia.

Anesthesia↗
PubMed1997

Distribution of macromolecular components in the muscle-bone junction of human masticatory muscles.

At the muscle-bone junction, the attachment is composed of macromolecular components that differ from those in masticatory muscles. In the temporal and lateral pterygoid muscles, numerous fine fibers form complex arrangements between collagenous bundles and the tendon-bone junctions. Collagenous bundles are directly inserted into the bone tissue at the site of the adhesive attachment. Reticular fibers are arranged irregularly and cover the collagenous bundles as a network. Numerous collagenous fibers are also tightly connected with the bundles that are found near the muscle-bone junction of the lateral pterygoid muscle. Strong or moderate staining for collagen types I, III, and V, tenascin, laminin, and fibronectin was observed in close association with the border of the bone matrix. Different distributions of these macromolecular components were found in each masticatory muscle. The results suggest that the morphological properties of the muscle-bone junction of each muscle reflect the tension or the stretch applied to a mandible bone. The distribution of macromolecular components in each muscle also reflects the form and calcification of the mandibular bone during aging.

Alveolar Process↗
PubMed1992

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↗
PubMed1980

The occurrence of muscle spindles in the masticatory muscles: a methodological study of different staining techniques.

A method, based on experiment, for more reliable and less time-consuming staining and examination of histological specimens for locating muscle spindles by light microscopy is presented. Sections from the masseter and temporal muscles of the rat were stained with different methods and studied in random order. The method giving the highest number of muscle spindles during scrutiny of the slides (Weigert's iron haematoxylin and van Gieson) is recommended for future studies on the numbers of muscle spindles in a given muscle.

Animals↗
PubMed1980

Number and distribution of muscle spindles in the masticatory muscles of the rat.

The frequency and distribution of muscle spindles in the muscles of mastication of the rat have been studied. The average number of spindles found was 110 in the masseter, 75 in the temporalis and 25 in the medial pterygoid muscle, the spindles being predominantly in the medial parts of these muscles. No muscle spindles were found in the lateral pterygoid or posterior digastric muscle, and only isolated spindles were found in a few of the anterior digastric muscles. These differences between the jaw-closing and the jaw-opening muscles are intriguing and ask for further investigation of the role of the muscle spindles in mastication.

Animals↗
PubMed1981

[Effect of head posture on muscle tonus of the masticatory muscles].

The integrated electromyographic study allows to determine action of the variation amplitudes of tonic activity of the masseter muscles, the anterior temporalis muscles and the trapezius muscles induced by angular cephalic displacements of 10 degrees in the three space planes, in sitting position (P.A) and upright position (P.D.). The direction of the variations can be simultaneously positive or negative according to the vertical reference position (P.R.) in the different muscles studied. The masseter muscles showed the largest variations of the P.A. to the P.D. Twenty per cent of the subjects can be classified in a hypertonic category.

Adult↗
PubMed2001

Morphology and physiology of masticatory muscle motor units.

Motor unit territories in masticatory muscles appear to be smaller than territories in limb muscles, and this would suggest a more localized organization of motor control in masticatory muscles. Motor unit cross-sectional areas show a wide range of values, which explains the large variability of motor unit force output. The proportion of motor unit muscle fibers containing more than one myosin heavy-chain (MHC) isoform is considerably larger in masticatory muscles than in limb and trunk muscles. This explains the continuous range of contraction speeds found in masticatory muscle motor units. Hence, in masticatory muscles, a finer gradation of force and contraction speeds is possible than in limb and in trunk muscles. The proportion of slow-type motor units is relatively large in deep and anterior masticatory muscle regions, whereas more fast-type units are more common in the superficial and posterior muscle regions. Muscle portions with a high proportion of slow-type motor units are better equipped for a finer control of muscle force and a larger resistance to fatigue during chewing and biting than muscle portions with a high proportion of fast units. For the force modulation, masticatory muscles rely mostly on recruitment gradation at low force levels and on rate gradation at high force levels. Henneman's principle of an orderly recruitment of motor units has also been reported for various masticatory muscles. The presence of localized motor unit territories and task-specific motor unit activity facilitates differential control of separate muscle portions. This gives the masticatory muscles the capacity of producing a large diversity of mechanical actions. In this review, the properties of masticatory muscle motor units are discussed.

Animals↗
PubMedDate not supplied

[Ultrastructural disorders in the muscle fiber of the masticatory muscles in mandibular fractures].

Basic impairments of the muscular fibre in fractures of the lower jaw with different localization within terms from several hours to several weeks in persons with various clinical course were studied with help of electronic microscopy. Following treatment of the injury with a "quiet" course, in the tissues studied there was activation of reparative processes up to normalization of the submicroscopic structures. Despite the given treatment, the injury accompanied with predominance of destructive changes in the muscular tissue. In the muscles, a disturbed permeability of depolarization waves was revealed, they causing contraction and relaxation of the muscles.

Biopsy↗
PubMed2002

Effects of experimental muscle pain on electromyographic activity of masticatory muscles in the rat.

The aim of the present study was to investigate the effects of noxious chemical stimulation of a jaw muscle on postural electromyographic (EMG) activity from several masticatory muscles in lightly anesthetized rats. Unilateral injection of a substance known to induce acute muscle pain (5% NaCl) or longer duration of pain with inflammation (mustard oil) was made into the masseter muscle. The changes in EMG activity following the injection were recorded from the injected and contralateral masseter muscles and the ipsilateral digastric muscle. The algesic chemicals produced a significant but transient increase in EMG activity in all three muscles. The data from the present study and similar observations from clinical and experimental human studies suggest that increased activity from muscle nociceptors is not sufficient to produce a prolonged increase in postural EMG activity. Therefore, the development and maintenance of chronic jaw muscle pain does not appear to result from a feedback cycle mechanism.

Action Potentials↗
PubMed1979

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↗
PubMed1994

Characterization of human oro-facial and masticatory muscles with respect to fibre types, myosins and capillaries. Morphological, enzyme-histochemical, immuno-histochemical and biochemical investigations.

This study provides a comparative characterization of four human oro-facial muscles, one masticatory muscle (the masseter) and two limb muscles, with respect to muscle fibre types, myosin isoforms and capillary supply. Enzyme-histochemical methods were used to evaluate the myofibrillar ATPase fibre type composition. Immuno-histochemical techniques were used to determine the expression of myosin heavy chain (MHC) isoforms in the different fibre types. The contents of MHCs and myosin light chains (MLC) in different muscles were analysed with electrophoretic methods. In addition, the capillary bed of the muscles was evaluated using both enzyme- and immuno-histochemical techniques. The fibre type compositions of the oro-facial and masseter muscles were found to be qualitatively and quantitatively different from each other and from those of limb muscles. In general, the oro-facial muscles contained a predominance of unusually high oxidative type II fibres, with a staining reaction for ATPase in between that of type IIA and type IIB fibres, termed type IIAB. In fact, one of the oro-facial muscles, the zygomatic minor, showed the highest type II fibre proportion ever reported in humans. This fibre type pattern is in contrast to that of the masseter muscle, which contains a majority of type I fibres, small diameter low oxidative type IIB fibres and a significant proportion of ATPase-intermediately stained fibres, termed IM, and IIC. Inter- and intra-muscular variability in fibre size and shape was considerable in both the oro-facial and masseter muscles. The oro-facial muscles were devoid of muscle spindles. The immuno-histochemical and biochemical analyses showed a characteristic myosin composition of each muscle. Notably, the results indicated the presence of a previously undetected fast MHC isoform in the oro-facial muscles, tentatively termed "fast F". The masseter contained unusual myosin isoforms, such as fetal and alpha-cardiac MHCs, and unique combinations of MHC isoforms which were not found in the limb or oro-facial muscles. The type IM and IIC fibres co-expressed slow and fast A MHCs in the oro-facial and limb muscles, but slow and a "fast B like" MHC in the masseter. Individual fibres in the oro-facial and limb muscles contained one or two MHC isoforms, whereas individual fibres in the masseter co-expressed up to four different MHC isoforms. On the basis of their pattern of expression of MHC isoforms, up to five fibre types could be distinguished in the oro-facial and limb muscles and eight in the masseter.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphatases↗
PubMed1987

Dental stability and maximal masticatory muscle activity.

The electromyographical (EMG) activity of masticatory muscles during full clenching in the retruded contact position (RCP) and intercuspal position (IP) with and without a posterior stabilizing splint was studied. The linear envelope EMG signal from three bilateral muscles was recorded (masseter, anterior temporal and posterior temporal). Thirty-seven subjects were evaluated. Clenching in the RCP without the splint and with the presence of an unstable occlusal contact inhibited the masseter muscle activity and reduced anterior temporal and posterior temporal muscle activity. The masticatory muscle activity returned to normal when clenching in the RCP with a splint that permitted stability in the dentition. EMG activity was the same in the IP with and without the splint. The results indicate that the determinant of maximal masseter isometric muscle contraction is the amount of stability in the dentition rather than the jaw position. If the dentition takes the major role of stabilizing the mandible, i.e., there is good intercuspation, the masseter muscle can exert maximal isometric contraction. If the stability is not provided by the dentition, i.e., there is a premature contact, the jaw muscles must contribute to the stabilization and reduce the magnitude of the maximal contraction to avoid damage to the structures involved in the compensatory stabilization.

Dental Occlusion↗
PubMed1999

[Study on masticatory muscles and tooth long axis of miniature pigs].

OBJECTIVE: The similarities of masticatory muscles and teeth orientations between miniature pigs and human beings were studied in order to evaluate the use of miniature pigs in oral biomechanics research. METHODS: By means of anatomy, the shapes, start-stop points and orientations of muscle of major masticatory muscles of miniature pigs were measured. Inclination of upper and lower teeth long axis was studied with lateral xray film of mandibles. RESULTS: The main masticatory muscles of miniature pigs include masseter muscle, temptory muscle, lateral pterygoid muscle, medial pterygoid muscle and zygomaticomandibular muscle. The angles of masticatory muscles and base plane are 63.9 degrees in massater muscle, 114.55 degrees in temple muscle, 64.4 degrees in medial pterygoidp muscle. The long axises of miniature pigs teeth are 6.1 degrees in the upper first molar, 6.5 degrees in the lower first molar, 7.3 degrees in the upper third premolar, 3.8 degrees in the lower third premolar. CONCLUSION: The masticatory muscles of miniature pigs are similar with human being in the shape, start-stop point and orientation of muscle force. The third premolar and the first molar of miniature pigs inclinate mesially, and are similar with the first premolar and the first molar of the human beings. Miniature pigs can be used as an animal models which can explain some problems of gnathostomatic system of human beings.

Animals↗
PubMed1995

Muscle fibre expression of transforming growth factor-beta 1 and latent transforming growth factor-beta binding protein in canine masticatory muscle myositis.

Masticatory muscle myositis (MMM) is presumed to be an immunologically mediated canine myopathy but is of unknown origin. Severe atrophy and degeneration of masticatory muscle fibres, infiltration of eosinophilic granulocytes, and proliferation of the fibrous interstitial tissue are the hallmarks of MMM. Transforming growth factor-beta (TGF-beta) is a multifunctional regulatory peptide controlling myogenesis, inflammation and tissue repair. We investigated immunocytochemically the expression of TGF-beta 1 and latent transforming growth factor-beta binding protein (LTBP), a TGF-beta modulator protein, in cases of MMM. The study demonstrated the presence of TGF-beta and LTBP in muscle fibres. infiltrating leucocytes and extracellular matrix in MMM, and suggested that TGF-beta and LTBP play a role in muscle tissue repair, inflammation and fibrogenesis in MMM.

Animals↗
PubMed2000

Intermuscular and intramuscular differences in myosin heavy chain composition of the human masticatory muscles.

Among and within the human masticatory muscles a large number of anatomical differences exists indicating that different muscles and muscle portions are specialized for certain functions. In the present study we investigated whether such a specialization is also reflected by intermuscular and intramuscular differences in fibre type composition and fibre cross-sectional area. Fibre type compositions and fibre cross-sectional areas of masticatory muscles were determined in eight cadavers using monoclonal antibodies against myosin heavy chain (MyHC). The temporalis, masseter and pterygoid muscles could be characterized by a relatively large number of fibres containing more than one MyHC isoform (hybrid fibres). In these muscles a large number of fibres expressed MyHC-I, MyHC-fetal and MyHC-cardiac alpha. Furthermore, in these muscles type I fibres had larger cross-sectional areas than type II fibres. In contrast, the mylohyoid, geniohyoid and digastric muscle were characterized by less hybrid fibres, and by less fibres expressing MyHC-I, MyHC-fetal, and MyHC-cardiac alpha, and by more fibres expressing MyHC-IIA; the cross-sectional areas of type I and type II fibres in these muscles did not differ significantly. Compared to the masseter and pterygoid muscles, the temporalis had significantly larger fibres and a notably different fibre type composition. The mylohyoid, geniohyoid, and digastric muscles did not differ significantly in their MyHC composition and fibre cross-sectional areas. Also intramuscular differences in fibre type composition were present, i.e., a regionally higher proportion of MyHC type I fibres was found in the anterior temporalis, the deep masseter, and the anterior medial pterygoid muscle portions; furthermore, significant differences were found between the bellies of the digastric.

Aged↗