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At least 91 records · Page 5Linked to original sources
PubMed2006

Size and orientation of masticatory muscles in patients with mandibular laterognathism.

Size measurements of jaw muscles reflect their force capabilities and correlate with facial morphology. Using MRI, we examined the size and orientation of jaw muscles in patients with mandibular laterognathism in comparison with a control group. We hypothesized that the muscles of the deviated side would be smaller than those of the non-deviated side, and that the muscles of both sides would be smaller than in controls. In patients, a comparison of deviated and non-deviated sides showed, in orientation, differences for masseter and medial pterygoid muscles, but, in size, differences only for the masseter muscle. Nevertheless, muscle sizes in patients were much smaller than in controls. Lateral displacement of the mandible can explain the orientation differences, but not the smaller muscle size, in patients. It is possible that the laterodeviation initiates an adaptive process in the entire jaw system, resulting in extensive atrophy of the jaw muscles.

Adaptation, Physiological↗
PubMed1991

Electromyography of masticatory muscles in craniomandibular disorders.

Patients presenting to the otolaryngologist with complaints such as otalgia, dizziness, tinnitus, or fullness in the ear may be experiencing the effects of craniomandibular disorders. These disorders can involve dysfunction in the delicate interrelationship of the skull, mandible, cervical vertebrae, and neuromuscular apparatus and can present as myofacial pain. Electromyographic recordings using surface electrodes were made bilaterally on the masseter, anterior temporalis, and digastric muscles in 641 craniomandibular patients, before and after transcutaneous electrical neural stimulation, at their initial presentation and following the insertion of mandibular orthopedic appliances. In the presenting patient, muscle-resting levels significantly decreased from hyperactive levels with transcutaneous electrical neural stimulation therapy. The creation of a new occlusal position with an orthotic appliance was found to correlate with a significant reduction in otolaryngologic symptoms as well as an increase in maximum muscle activity in function and coordination of muscle groups during mandibular movement. Thus, clinical electromyographic studies are an important aid in the treatment of craniomandibular disorders.

Electromyography↗
PubMedDate not supplied

Electromyography tension and frequency spectrum analysis of some masticatory muscles at rest, isotonic and isometric contractions.

On a population of 52 subjects surface electromyographic recordings of temporals and masseters, simultaneously with mandible dynamic of closure and clenching, were performed, in order to study tension and frequency behaviour in three postural conditions: rest, isotonic and isometric contractions. Frequency was studied using the median resulting from FFT calculation, and a new computing method, which presents the proportion of frequencies making up the whole EMG signal, by steps of 50 Hz. Tension was calculated as well. The results permit us to draw the following conclusions: 1. a period of EMG silence was present in 51 of 52 subjects at mandible closure (SPA--Silent Period Area); 2. SPA onset was before teeth contact (22.5 msec., during the motion of the mandible), while its end was after closure (10.2 msec., during motionless phase of clenching). This allowed to use the SPA as a tool to clearly distinguish isotonic from isometric contraction; 3. the comparison of tension and frequency, expressed as median, showed that at rest a muscle presents low frequency and low tension. In active contraction both increase their values. Nevertheless, in active contraction, while no differences were found in frequency behaviour, tension showed a difference: although higher than at rest, isotonic contraction presented lower values than during isometric contraction; 4. the study performed by the new program showed that the low frequency at rest was due to the high proportion (30-40%) of frequencies of less than 50 Hz, while the increase at function was due to the parallel increase of frequencies comprised between 100 and 250 Hz. Because it is known that muscles are composed of fibers at low frequency and at high frequency of discharge, which play different functional roles, the last finding suggests that the mathematical analysis of the spectrum of frequencies, could provide a functional-histological image of the muscle.

Adolescent↗
PubMed1990

[Postnatal development of the masticatory muscles of the Wistar rat (Rattus norvegicus Berkenhout). A histochemical study].

Muscle biopsies of the mandible adductors of the Wistar rat (Rattus norvegicus Berkenhout) have been analyzed enzyme-histochemically for the investigation of the postnatal development (42.-126. d post partum) of their muscle fibers with special regards to the fiber types. The following methods have been used in this investigation: myofibrillar adenosine triphosphatase (ATP-ase) with different pre-incubations, Sudan black B (triglycerides), periodic acid-Schiff reagent (PAS) (glycogen), Gomori modified Trichrome staining. Quantitative analysis of muscle fibre-type composition and muscle fibre size was done from different regions of muscle sections. Estimation of the fiber size was carried out by measuring the minimum diameter of each type of muscle fibre.

Adenosine Triphosphatases↗
PubMed1989

Blood-flow and metabolic response in a contracting canine masticatory muscle.

The mechanical and metabolic characteristics of the canine masseter muscle of seven adult dogs, aged 3 years, weighing 45-55 kg, were evaluated by electrically provoked contractions. The masseter muscle was exposed by careful surgery and stimulated by two silver electrodes placed in the anterior and posterior aspects of the muscle. The bite force was measured with a force transducer. Glycogen, glucose-contents together with lactate, pyruvate, creatine phosphate, NADH and NAD were analysed fluorimetrically. Intra-muscular oxygen tension was continuously recorded by a flexible silver electrode. Blood-flow was measured by the 133Xenon clearance technique. Biopsies were taken at rest and after stimulation. The registered bite force revealed an initial peak, representing maximal force production and thereafter a rapid decline in power output. During the following stimulation events the bite force curve showed decrease in amplitude concerning maximal force as well as duration of bite force production. The blood-flow and oxygen tension were significantly reduced at the end of stimulation. However, after recovery these parameters were normalised to initial values. The glycogen and glucose were depleted after stimulation. The lactate concentration increased about three to four times. The observed changes in NAD and NADH indicate a hypoxic situation in the muscle cells. The oxygen deficit in conjunction with the intramuscular blood-flow impairment and the metabolite variations reflect the energy and redox state in the muscle and may contribute to the decline in bite force production.

Animals↗
PubMed1987

[Functional morphology of the maxillo-mandibular apparatus of the mini-Lewe minipig. 2. Structure of the masticatory muscles of adult animals].

The masseter muscle is the most powerfully developed of the jaw muscles in the miniature pig MINI-LEWE. Its internal skeleton contains 5 Sehnenspiegel. The zygomatico-mandibular muscle acts as a link between the masseter and temporal muscles. The pinnate structure of the temporal muscle results from the internal tendons, which attach to the coronoid process. The medial pterygoid muscle with its 7 Sehnenspiegel has the most complex pinnate structure. The lateral pterygoid muscle has small tendinous slips only in the regions of its origin and attachment.

Animals↗
PubMed1988

[Functional morphology of the maxillomandibular apparatus in the mini-Lewe minipig. 6. Intramuscular nerve ramifications in the masticatory muscles of adult animals].

The masseter muscle is innervated by branches of 3 nerves. The zygomaticomandibular muscle must be regarded as part of the masseter as it is supplied by 2 branches of the massetericus nerve. Two branches of the medial pterygoid nerve enter the medial pterygoid muscle medially. The lateral pterygoid muscle is supplied by the lateral pterygoid nerve, which enters the muscle dorsally perpendicular to the muscle fibres. Five branches of the profound temporal nerves enter the temporal muscle from the ventral and medial sides. The branches of all nerves proceed parallel to each other in the dorsal direction towards the origin of the muscle.

Animals↗
PubMed1980

[Role of different types of infraorbital nerve fibers in synaptic activation of masticatory muscle motoneurons].

The PSPs of the masseter and digastric motoneurons evoked by stimulation of the infraorbital nerve by stimuli from 1 to 10 thresholds were studied in cats anesthetized with chloraloze and nembutal. Masseter motoneurons were divided into two groups. The first group masseter motoneurons responded to 1-2.5 threshold infraorbital nerve stimulation by short latent EPSPs. An increase in the impulse strength to 3-9 thresholds led to appearance of IPSPs with 2.8-3.5 ms latency in these motoneurons. The second group masseter motoneurons responded to 3.9 threshold stimulation of the infraorbital nerve by IPSPs with 6.8 ms latency. The strength of stimuli below 3 thresholds evoked no PSPs in these neurons. Stimuli of 1.1-2.0 thresholds evoked EPSPs in digastric motoneurons but an increased stimulation led to generation of action potentials. It is supposed that existence of different inputs is a basis for functional diversity of jaw-closing and jaw-opening reflexes.

Animals↗