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At least 19 recordsLinked to original sources
PubMed1988

An experimental orthopedic treatment of the rat mandible using a functional appliance alters the fibre and myosin types in masticatory muscles.

Masticatory muscles mediate the action of functional orthopedic appliances on mandible growth. When young rats were treated for four weeks with a postural hyperpropulsor of the mandible, an appliance designed to increase condylar cartilage growth rate, the proportion of fast non-fatigable fibres in the lateral pterygoid muscle increased significantly. Concomitantly, the amount of slow-myosin light chains increased in fibre extracts. This slow myosin originated from IIA fibres. By functional orthopedic treatment, the lateral pterygoid muscle was enriched in less fatigable fibres; the changes observed in the lateral pterygoid muscle were close to changes observed in other muscles after training.

Adenosine Triphosphatases↗
PubMed1998

[Masticatory muscles. Part IX. Pain in the jaw muscles].

Masticatory muscle pain is considered as a local expression of myofascial pain. The relationship with Myofascial Pain Syndrome and Fibromyalgia is not well understood. Muscle pain is generated through nociceptors served by small-diameter fibres, where processes of sensitization and neurogenic inflammation are important. In contrast to the 'vicious circle' concept, limitation of movement and loss of muscular power seem to be the result of the pain (pain-adaptation model). The diagnosis of muscle pain is made by algometry, while treatment should be simple, reversible and non-invasive.

Diagnosis, Differential↗
PubMed1985

[Animal experiment studies on the effect of unilateral tooth extraction on the growth of the skull and masticatory muscles. III. The masticatory muscles].

All continuous teeth were unilaterally extracted on the right side of the upper and lower jaws of 57 male and female Vietnamese belly pig. The animals were slaughtered 6, 7, 8, 9, 10, 11 and 12 after the extraction. Our investigations into quantitative changes in the masticatory musculature after unilateral extraction showed the dry weight of the musculature on the extraction side was reduced. This reduction was greatest in the case of the M. temporalis. The findings relating to the muscles are consistent with the results of the skull evaluations reported in the first 2 publications, with indicated that tooth extraction leads to only local changes in the jaw during postnatal development. The findings published in the 3 publications of this series relating to the bones and muscles are discussed.

Animals↗
PubMed1998

[Masticatory muscles. Part VII. Masticatory muscles and mastication. How do we get small pieces of food?].

One of the functions of the masticatory system is to prepare food for swallowing by crushing it into small pieces to be moistened with saliva. The degree of fragmentation of the food particles depends on factors like the chewing force generated by the closer muscles, the jaw movement, and the morphological aspects of the teeth. The jaw movement is the result of a precise neuromuscular control of the various chewing muscles. Experimental research showed that the muscle activity needed to crush the food particles exists of two components: an anticipating component and a component evoked by the food resistance. The anticipating muscle activity is observed only if food resistance is expected. The muscle activity evoked by the food starts on average 25 ms after food contact. The amount of peripherally induced muscle activity linearly increases as a function of the food resistance. This part of the muscle activity is controlled by sensory information of the masticatory system.

Bite Force↗
PubMed1997

[Masticatory muscles. Part VI. Masticatory muscles and movement of the lower jaw].

The movement paths of the kinematic center of the temporomandibular joint were recorded by means of a jaw movement recording system (OKAS-3D) under 3 conditions: 1. free open and close movements; 2. free opening and loaded closing movements (subjects closed against a small, manually applied, downward directed force on the chin); and 3. during chewing of chewing gum. During free jaw movements, the opening path of the kinematic center lies above the closing path. During loaded closing movements, the opening and closing paths coincide. This indicates that during opening and loaded closing, the condyle-disc complex is slightly pressed against the articular eminence. However, during free closing, there is more space between the articulating surfaces. During gum chewing, the opening and closing paths of the condyle coincide on the balancing side, on the working side they don't. Thus, the joint on the balancing side is loaded and the joint on the working side is not.

Biomechanical Phenomena↗
PubMed1997

[Masticatory muscles. Part IV. The masticatory muscles do not work homogeneously].

The temporalis and masseter muscles have a complex architectural design with large attachment areas. As a consequence, each of these muscles is capable of producing a large number of mechanical effects. In addition, within each muscle the muscle fibres and sarcomeres undergo different excursions during jaw movements. This leads to intramuscular differences in the possible excursion range and the capacity to produce force. Depending on the desired motor task, the nervous system is able to vary both the magnitude and direction of muscle force by selective activation of specific muscle portions. The anterior temporalis and the superficial and deep masseter are capable of generating large forces, e.g. during biting and chewing. The posterior temporalis and the anterior and posterior deep masseter are suited to establish a precise adjustment of forces and movements during laterotrusion and protrusion/retrusion.

Biomechanical Phenomena↗
PubMed1997

[Masticatory muscles. Part III. Biomechanics of the masticatory muscles].

The masticatory muscles are able to produce forces. These forces may cause movements of the lower jaw. Furthermore, they can be applied by the teeth for the generation of bite or chewing forces. During these kind of processes the temporomandibular joints will be loaded also. The interaction between forces and movements in the masticatory system is complex but obeys the relatively simple laws of mechanics. By application of these laws the development of joint loading, force patterns and movements during masticatory function and dysfunction can be understood. This is illustrated by a few examples of both statical and dynamical masticatory performance.

Biomechanical Phenomena↗
PubMed1996

Effects of NK433, a new centrally acting muscle relaxant, on masticatory muscle reflexes in rats.

The effects of (-)-(R)-2-methyl-3-(1-pyrrolidinyl)-4'- trifluoromethylpropiophenone monohydrochloride (NK433), a novel centrally acting muscle relaxant, on masticatory muscle reflexes were investigated in rats. NK433 inhibited the monosynaptic tonic vibration reflex of the masseter muscle and the polysynaptic tonic periodontal masseteric reflex. These reflexes are increased by gamma-motor activity. NK433 had a weak inhibitory effect on the polysynaptic jaw opening reflex evoked by electrical stimulation of the tooth pulp, which is little related with gamma-motor activity. Eperisone-HCl depressed the three types of masticatory muscle reflexes. When intravenously administered, eperisone-HCl was equipotent to NK433, but the effect of eperisone-HCl was shorter-lasting than that of NK433. The effect of intragastrically administered NK433 on the periodontal masseteric reflex was about three times stronger than that of eperisone-HCl. These results suggest that NK433 inhibits masticatory muscle reflexes controlled by the gamma-motor system and thus may ameliorate the temporomandibular joint syndrome in man.

Animals↗
PubMed1997

[Masticatory muscles. Part II. Functional properties of the masticatory muscle fibers].

The masticatory muscles in human beings and in other mammals show a number of specific adaptations. Their muscle fibres contain at least four different isoforms of myosin heavy chain (MHC) and many fibres express more than one kind simultaneously. This implicates a continuous range of fibre contraction speeds for these muscles. Most or all fibres have a high oxidative capacity and consequently are very resistant against fatigue. The fast muscle fibres of the masticatory muscles appear to have smaller calibers than the slow ones. This condition is particular and points to mild atrophy. The motor units of the jaw muscles are characterised by large fibre numbers per unit, but concentrated into small subvolumes of muscle. Because of the anatomical heterogeneity of the muscles, motor units are capable of generating quite a variety of force directions. The fibres of jaw muscle motor units often belong to different fibre types, as far as their MHC-composition is concerned. For this reason, the units cannot be subdivided into clear-cut types, but show a continuous range of contraction times.

Bite Force↗
PubMed1997

[Masticatory muscles. Part V. Geometry of the masticatory muscles and cranial morphology].

Studies focussed on the interactions between masticatory function and the variation in craniofacial height have received an important impulse by the availability of non-invasive imaging techniques like CT and MRI. These techniques allow for in vivo determination of the cross-sectional area and spatial orientation of the human jaw muscles. In recent MRI studies it has been established that the jaw muscles of long-face subjects are up to 30% smaller than those of normal individuals, while the position of the muscles was fairly comparable in both groups. The maximum bite force of long-face subjects is roughly half that of normals. The observed variation of the in vivo data of normal and long-face jaw muscle geometry does explain only half of the difference in their average maximum bite force. The jaw muscles of long-face and normal subjects are presumably different with respect to their force generating capacity per unit of cross-sectional area, which may be attributed to a different muscle fiber type composition.

Bite Force↗
PubMed1983

Programming of antagonist muscle stiffness during masticatory muscle unloading in man.

The activity of the masseter and digastric muscles was monitored carrying out a controlled, isometric biting task. In 7 out of 10 subjects, the level of activity in the digastric muscle, during the phase of isometric biting, was greater when the subjects expected the resistance between their teeth to yield suddenly than when they were confident that the resistance would not yield. It is therefore concluded that the co-activation of the digastric muscle which occurs during forceful isometric bites can be modified in accordance with the subject's expectation of the outcome of the bite.

Adolescent↗
PubMed2002

A case of atrophy of the masticatory muscles due to a masticatory habit.

We present a case of atrophy of the masticatory muscles due to a masticatory habit. The patient has had only left side molars for about 40 years. The atrophy of the masticatory muscles was detected incidentally when a brain radiological examination was performed. The patient had no subjective complaints on mastication.

Aged↗
PubMed1988

[Osteotomy healing of the lower jaw and the adaptation of the masticatory muscles after miniplate osteosynthesis in rabbits. II. Response pattern of the masticatory muscles (M. masseter)].

16 operated 4 control animals of both sexes were included in the study following osteotomy of the lower jaw and subsequent miniplate osteosynthesis. In addition, muscle tissue excised from 8 rabbits was evaluated at the time of the operation as additional normal material. The study was conducted over 4, 8, 12 and 24 weeks, after which periods the animals were killed and their left and right masseters examined and compared in histological, histochemical and morphometric terms. The masticatory muscles of the control rabbits displayed a marked sex dimorphism. The males had strikingly large, predominantly type-2 fibres, whereas the fibre diameters in the females were found to differ less clearly, with type-1 fibres being predominant. In terms of muscle regeneration, it was found that following soft-part trauma small localized defects (biopsy) had healed completely after 12 weeks. In the residual parenchyma, signs of adaptation to a changed mastication as a result of the experimental operation (osteotomy of the lower jaw, miniplate osteosynthesis, muscle biopsy) could be identified. Atrophy as a result of non-use was found to occur to a limited extent, whereas the number of type-2C fibres and fibre type transformations were raised significantly. After the surgery, the organization of the impaired muscle fibres was aided by a stabilization and rest positioning of the parts concerned. The muscle fibres reinnervation that followed was supported by functional exercise and nerve impulses.

Animals↗
PubMed1997

[Masticatory muscles. Part I. Functional anatomy of the masticatory muscles].

The anatomical design of the jaw-closing and jaw-opening muscles is of importance for their capability to produce forces and displacements. The length of the sarcomeres is a major determinant for both force and shortening range. The maximal work, force and shortening range each muscle is capable of producing, are proportional to the architectural parameters volume, physiological cross-sectional area and fiber length, respectively. Compared to the jaw openers, the jaw closers are characterized by shorter sarcomeres at the closed jaw, larger masses of contractile and tendinous tissue, larger physiological cross-sectional areas, shorter fibers and shorter moment arms. In addition, architectural features vary across the muscles of the same functional group and in some muscles significant intramuscular differences are found. In general, the jaw closing-muscles have architectural features that suit them for force production, whereas the jaw-opening muscles are better designed to produce velocity and displacement.

Bite Force↗
PubMed1990

[Electronic measurements of the masticatory muscles. 2: Interpretation of activity changes in the masticatory muscles].

In part II, a method is described which reduced the variations of the three determinants of the voltage/tension curves to the fluctuation of only one three dimensional variable. A way to estimate three dimensional regions for the fluctuations is shown. For a given level of significance, limits can be calculated that allow us to decide whether differences between post- and pre-treatment measurements are random or due to treatment.

Electromyography↗