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PubMed1983

Muscle spindle supply in the pig masticatory muscles.

This histological study was designed to define the anatomical background of the neuromuscular control mechanism involved in the non-ruminant omnivorous mastication, focusing on the muscle spindle supply to each muscle belly of the jaw muscles of 3 pig fetuses (near term). The jaw-closing muscle averaged 427 muscle spindles, 566 spindles, 703 spindles on one side of the face respectively: 160, 203, 240 in the temporalis, 122, 160, 248 in the masseter, 128, 154, 193 in the medial pterygoid, and 16, 49, 21 in the zygomaticomandibularis. No spindles were in the lateral pterygoid and the jaw-opening muscles.

Animals↗
PubMed2003

Effects of activator on masticatory muscle activity during daytime and sleep.

The purpose of this study was to investigate masticatory muscle activity with and without the use of an activator during daytime and sleep, and further to focus on the changes in muscle activity produced by the daytime use. The subjects in this study were 10 healthy males (mean age: 27.6 years). A portable electromyogram (EMG) recording device was used to record the activity from the right temporal, masseter and digastric muscles. After recording, the integrated EMG values (microV s) were measured. The muscle activity was lower during sleep than during daytime, irrespective of the use of the activator. In sleep-time, temporal and digastric muscle activity was significantly decreased, although masseter muscle activity presented no significant differences. With the activator in use, the digastric muscle activity tended to increase in comparison with the elevator muscles during daytime and sleep. Although the activity of both elevator muscles was diminished by use of the activator during sleep in all subjects, some subjects showed an increase during daytime. These results suggested that the activator should be used, if possible, not only during sleep, but also during daytime and clenched on consciously to obtain the adaptation and development of the masticatory muscles for the 're-training of the muscles' at a new favourable mandibular position.

Adult↗
PubMed1991

[Masticatory muscles of domestic sheep and swine in ontogenesis].

Age changes of morphometrical parameters of the masticatory muscles have been analyzed in domestic sheep and pigs of white large breed in the following age groups: 2-, 3-, 4-month-old fetuses, newborns, 4-month-old lambs, 10-month-old pigs, 18-month-old lambs, mature she-sheep and brood-sows. Uneven weight growth of the masticatory muscles in the sheep and pigs during the prenatal ontogenesis should be considered as a consequence of recapitulation of their phylogenesis, and in the postnatal ontogenesis it depends on changes in life conditions, type of nutrition, character of food and type of life. In newborn sheep the digastric, lateral, pterygoid and temporal muscles grow intensively, and in pigs--medial pterygoid and temporal ones. When they pass to roughage, in the former the mass of the musculus masseter major and medial pterygoid muscle increases, and in the latter--that of the musculus masseter major and temporal one. The masticatory muscles of the species studied increase in their mass especially intensively during the middle of the prenatal ontogenesis and during suckling period of their development. This should be taken into consideration in stock-breeding practice. In domestic pigs there is only one muscular belly in the digastric muscle. In sheep there are two bellies, separated one from another by means of a tendinous intersection, owing to crossing of the latter by the stylohyoid muscle.

Age Factors↗
PubMed2001

Effects of masticatory muscle function and bite-raising on mandibular morphology in the growing rat.

The aim of this series of investigations was to study the effect of masticatory muscle function on the growth pattern and on the internal structure of the mandible during growth. The muscular and dentoskeletal growth adaptation to prolonged bite-raising and the role of the functional state of the masticatory muscles in this adaptation were also to be elucidated. Differences in masticatory muscle function were induced in young rats by altering the consistency of the diet. Bite-raising was produced by the insertion of posterior bite blocks. Morphometric analysis of the internal bone structures of the mandible was performed on microradiographs, and videodensitometric analysis was performed on lateral radiographs and microradiographs. The effect of muscle function and bite-raising on mandibular growth was studied on a series of lateral cephalograms, superimposed on bone markers. Muscle belly, sarcomere and aponeurosis length adaptation to bite-raising was studied in situ with a digital caliper and under a microscope after fluorescent vital staining of the deep masseter muscle. A soft diet altered the pattern of growth of the mandible and reduced bone growth in the angular region. Transversal dimensions and cross-sectional area of the dentoalveolar process were smaller. Bone mass in areas possibly subjected to direct loads or bending forces was smaller. This was due to either less trabecular bone or thinner cortical bone. Only a few sites showed lower bone density. Posterior bite-blocks affected the size of the mandible as well as its growth pattern, and intruded lower molars. The soft diet influenced the effect of bite-blocks and caused less intrusion of upper molars and less inhibition of bone growth at the angular process. The deep masseter muscle adapted to bite-raising by elongation of the aponeurosis, but less in rats on a soft diet. Changes in masticatory muscle function affected the growth of the mandible in both the sagittal and transversal plane. Reduced loads on molars and condyle and smaller bending forces in other regions of the mandible possibly reduced the levels of stimulation of the osteocyte network and osteoblasts, thus inducing less trabecular bone and cortical bone formation in specific areas. In rats fed the soft diet, smaller increase in bone density represented an adaptation process in areas characterised by a lower bone apposition rate. The forces produced by the passive stretching of the masseter muscle affected the skeletal growth pattern and dental eruption. Weaker forces possibly produced by passive stretching of hypofunctional muscles resulted in more eruption of the upper molars and less inhibition of periosteal bone apposition in the angular region. Length adaptation in the masseter muscle through lengthening of the aponeurosis and dentofacial growth adaptation possibly decreased passive forces applied to teeth and skeletal structures, particularly in rats with higher functional demands. This may have caused a gradually decreasing effect of the appliance.

Adaptation, Physiological↗
PubMed1980

Further histochemical studies on masticatory muscles.

This paper describes a histochemical and histographic analysis of the masticatory muscles obtained from 78 early autopsy samples from subjects from 4 days to 87 years old. Five groups of muscles have been stuied: the temporalis, the medial and lateral pterygoid, the superficial bundle of the masseter and the mylohyoideus. All adult muscles have consistently shown a markedly increased number oftype II fibres and a disparity in the size of the two main fibre types, the average diameter of type II fibres being about half that of type I fibres. Fibres of intermediate size and stain were observed with myofibrillar ATPase at pH 9.40. A negative relation between the percentage of type II fibres and intermediate fibres was found, but not between the percentage of type I fibres and of intermediate fibres. Another negative relation was found between the number and the size of type II fibres, again not present in type I nor in intermediate fibres. In children, from 6 days old, an increased number of type II fibres and a definite disparity in the size of the two main fibre types were found. Intermediate fibres were present on the 17th day. Up to the age of 13 years, their diameter was greater than that of type I fibres. The analysis of the distribution and size modifications of the various fibre types seems to indicate a progressive adaptation of the masticatory muscles. This adaptation of the fibres to the successive reactions and to the various movements of the masticatory system is then discussed.

Adaptation, Physiological↗
PubMed1999

The influence of crossbite on the coordinated electromyographic activity of human masticatory muscles during mastication.

The analysis of the masticatory muscle activity in subjects with altered occlusal relationships could provide useful data of the functional impact of morphological discrepancies. Thirty subjects aged 16-18 years, with a sound, full permanent dentition, bilateral angle class I, and an overjet and overbite between 2 and 5 mm, were examined. The control group (10 male, 10 female) had no crossbite, while the crossbite group (four male, six female) had a posterior unilateral crossbite (five on the left side, five on the right side). The electromyographic activity of the left and right masseter and temporalis anterior muscles was recorded during 15 s of unilateral (left and right) chewing of gum, and expressed as a percentage of the maximum voluntary clench on cotton rolls. For each subject, the masticatory frequency, the confidence ellipse of the simultaneous differential left-right masseter and temporal activity (Lissajous figure), and an index of muscular symmetry, were computed to assess muscular coordination. In the crossbite subjects, the four analysed muscles appeared to contract with altered and asymmetric patterns. A large variability was found, and the confidence ellipses calculated for the chewing tests performed on the crossed sides were not significant, while the confidence ellipses of the uncrossed side chewing were different from the ellipses computed in the normal occlusion group. The altered occlusal relationship influenced the coordination of the masticatory muscles during chewing on both sides. The functional alteration was more apparent when the side with the altered morphology was directly involved, i.e. when chewing was performed on the crossbite side.

Adolescent↗
PubMed1981

Masticatory muscle silent periods in patients with MPD syndrome before and after treatment.

Masticatory muscle silent periods were compared in normal subjects and in patients with MPD syndrome before and after a variety of psychological, physiological, and pharmacological forms of therapy. All patients initially showed prolonged silent periods in one or more of the muscles. There was a direct relationship between prolongation and severity of symptoms. The temporalis (90.9%) and masseter (54.5%) were most frequently involved. In almost all instances the silent periods returned to the normal range following treatment.

Adult↗
PubMed1987

[The influence of the masticatory muscles on craniofacial growth. A microsurgical study in the rat].

Possible influence of masticatory muscles on facial growth was investigated in the rat by the formation of several experimental groups: excision of right masseter muscle of right temporal muscle, of both masseter muscles, of both temporal muscles and of both masseter and temporal muscles, section of inferior maxillary nerve and masseter transplantation. Results demonstrated that overall masticatory muscles provided equilibrium of masticatory function, any rupture of this equilibrium producing effects on mandibular growth and that of the facial mass.

Aging↗
PubMed1989

[Relationships between tooth loss and electromyographic activities of masticatory muscles].

For purpose of evaluating the characteristic of electromyographic activities of masticatory muscles with front or molar tooth loss, electromyographic activities of masticatory muscles and mandibular movements during tooth tapping and gum chewing were investigated in each group of tooth loss, and were compared with those of control group. The results were as follows. 1. In reference to the group with front tooth loss, 1) On tooth tapping, each S.D. of the time parameters of electromyographic activities of jaw closing muscles especially masseter and posterior temporalis was small, and that of jaw opening muscle was large. 2) On gum chewing, offset of jaw closing muscles' activities especially masseter and anterior temporalis were delayed. 3) On both tooth tapping and gum chewing, there was no difference in mandibular movements from control group. 2. In reference to the group with molar tooth loss, 1) On both tooth tapping and gum chewing, each S.D. of the time parameters of electromyographic activities of jaw closing muscles was large. 2) On tooth tapping, S.D. of opening ratio was large. 3) On gum chewing, both S.D. of chewing cycle and opening ratio were large.

Electromyography↗
PubMed1992

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↗
PubMed1996

Influence of the dynamical properties of the human masticatory muscles on jaw closing movements.

A dynamic six degrees-of-freedom mathematical model of the human masticatory system has been developed in order to study the contribution of the different masticatory muscles and their dynamical properties to the closing movement of the jaw. Muscles were included as forces acting according to their lines of action and the temporomandibular joints were modelled by linear elastic surfaces. Ligaments were not included. The geometry of the model was derived from a human cadaver. With this model symmetrical jaw closing movements were simulated. It was found that the normally observed jaw closing movement which includes a swing-slide movement of the condyle along the articular eminence, can be generated by various separate pairs of masticatory muscles. Among the masticatory muscles the different parts of the masseter as well as the medial pterygoid muscle appeared to be the most suitable to complete this action. The dynamical muscle properties appeared to provide a mechanism causing the movements to pass off more smoothly. The force/length relationship of muscle fibres, which also introduced a limit for protrusive excursions of the lower jaw, turned out to play a predominant role in this mechanism.

Biomechanical Phenomena↗
PubMed2006

Dental attrition models predicting temporomandibular joint disease or masticatory muscle pain versus asymptomatic controls.

AIMS: To determine whether patients with temporomandibular joint disease or masticatory muscle pain can be usefully differentiated from asymptomatic controls using multifactorial classification tree models of attrition severity and/or rates. METHODS: Measures of attrition severity and rates in patients diagnosed with disc displacement (n = 52), osteoarthrosis (n = 74), or masticatory muscle pain only (n = 43) were compared against those in asymptomatic controls (n = 132). Cross-validated classification tree models were tested for fit with sensitivity, specificity, accuracy and log likelihood accountability. RESULTS: The model for identifying asymptomatic controls only required the three measures of attrition severity (anterior, mediotrusive and laterotrusive posterior) to be differentiated from the patients with a 74.2 +/- 3.8% cross-validation accuracy. This compared with cross-validation accuracies of 69.7 +/- 3.7% for differentiating disc displacement using anterior and laterotrusive attrition severity, 68.7 +/- 3.9% for differentiating disc displacement using anterior and laterotrusive attrition rates, 70.9 +/- 3.3% for differentiating osteoarthrosis using anterior attrition severity and rates, 94.6 +/- 2.1% for differentiating myofascial pain using mediotrusive and laterotrusive attrition severity, and 92.0 +/- 2.1% for differentiating myofascial pain using mediotrusive and anterior attrition rates. The myofascial pain models exceeded the > or =75% sensitivity and > or =90% specificity thresholds recommended for diagnostic tests, and the asymptomatic control model approached these thresholds. CONCLUSION: Multifactorial models using attrition severity and rates may differentiate masticatory muscle pain patients from asymptomatic controls, and have some predictive value for differentiating intracapsular temporomandibular disorder patients as well.

Adolescent↗
PubMedDate not supplied

Canine muscle fiber types and susceptibility of masticatory muscles to myositis.

The myofiber type composition was studied in 42 different muscles of the dog to determine if there are unique features that might explain the preferential involvement of the muscles of mastication by inflammatory myopathies. The principal myofiber types for most muscles studied were type 1 and type 2A and, to a lesser extent, type 2C, whereas the dorsal group of muscles innervated by the mandibular nerve (Mm. temporalis, and tensor veli palatini) was composed only of type 2C myofibers and a variant of the type 1 myofiber whose staining intensity was not fully reversed after preincubation in acid media. The distribution of this myofiber type composition was associated with the innervation and embryologic development of the dorsal muscles innervated by the mandibular nerve. This unique myofiber type composition could provide the basis for the preferential susceptibility of these muscles to agents (e.g., immune and/or infectious) that produce myositis; however, further studies are required to assess that possibility.

Animals↗
PubMed1980

Biomechanical analysis of the main masticatory muscles in the rabbit.

The main masticatory muscles of the Rabbit (Oryctolagus cuniculus L.) were divided into their 25 component bundles per side. 5 dry skulls were used to determine points of origin and insertion which were then projected onto 3 planes perpendicular to each other, for the establishment of a biomechanical model. By interpreting this model and by examining various mandibular movements, the bundles were classified into 16 functional groups. The findings of other biomechanical studies are contrasted with the results of the study.

Animals↗
PubMed1986

Masticatory muscle function and craniofacial morphology. An experimental study in the growing rat fed a soft diet.

The present series of investigations was performed in order to study the relationship between masticatory function and craniofacial morphology, and to elucidate the mechanism underlying possible functional changes in the craniofacial growth in rats fed a soft diet. The experimental model chosen was comprised of young rats with altered masticatory function, induced by changing the consistency of the diet. Possible influences on the craniofacial growth were studied longitudinally by x-ray cephalometry, and the bone graft reaction in the facial skeletal regions of rats was assessed in sutures and cortical bone by vital stain, micro-radiography and routine histology. The attrition and eruption rate of the rat incisors were measured "clinically", and the effect of an increased attrition was tested cephalometrically, to see whether it influences the craniofacial growth. In order to evaluate the forces developed by the masticatory muscles the active tetanic tension was measured after electrical stimulation. The muscle fibre composition and the fibre size of the masseter and digastric muscles were examined after enzyme histochemical analysis. The craniofacial morphology and the growth pattern of the rats fed a soft diet were found to be changed to a more orthocranial one, while a decreased bone apposition was found in the angle of the mandible and the upper viscerocranium, with an alteration in the cranial sutures. The morphological changes observed were independent of the attrition and eruption rate of the rat incisors but seem to be related to the low masticatory forces developed by the rats fed a soft diet. The alteration in the "biting" force level was possibly due to the masticatory muscles changes in the muscle fibre types and the smaller size of the fibres, caused by the decreased functional demand on the rats fed a soft diet. Thus, it seems that the alteration in the masticatory function caused structural changes in the masticatory muscles, as well as changes in their contractive capacity. These may be considered as the results of prolonged centrally decided functional alteration brought about by changing the consistency of the diet. The reduced functional forces and the changes in the masticatory muscle contraction caused a low functional strain on the bone and less tension on the periosteal membrane. This tension in the periosteal membrane has also been shown to regulate the displacement of bones in the craniofacial region. The change in the masticatory function may have induced changes in the interosseous movements, which can be underlying reason for the obliterative osteogenesis in the internasal suture.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2004

Masticatory muscle right-left differences in controls and hemifacial microsomia patients.

One aim of this study was to assess right-left differences in the volume of masticatory muscles in controls so as to be able to distinguish between normal variations and pathological differences. The other aim was to compare the masticatory muscle volume of the nonaffected side of hemifacial microsomia patients with the smaller side of controls so as to test the compensation hypothesis. The study group consisted of 39 children with hemifacial microsomia and the control group of 52 children. Computed tomography scans were made using a Philips Tomoscan 350 and a Pro Speed S Fast Spiral General Electric scanner. The normal right-left differences in volume of the masticatory muscle of the controls, calculated as a percentage of the total, demonstrated small mean differences of 2.57% to 2.88% (SD:1.98-2.74). For hemifacial microsomia patients, the relative difference was about 10 times the difference for controls. For controls, the averages of the right-left differences (%) were all below the generally accepted SEM of 4%. Testing the compensation hypothesis of all effects, only the age effect was multivariately significant (P < 0.001). No overcompensation of the masticatory muscles of the nonaffected side of hemifacial microsomia patients could be demonstrated.

Adolescent↗
PubMed1998

Electromyographic investigation of masticatory muscles in unilateral cleft lip and palate patients with anterior crossbite.

OBJECTIVE: To evaluate the characteristics of masticatory muscle activity in operated unilateral cleft lip and palate (UCLP) patients with anterior crossbite compared with normal individuals. SUBJECTS: Sixteen male and 13 female Chinese patients with UCLP and anterior crossbite. Fifteen male and 13 female Chinese individuals without cleft abnormalities served as a control group. DESIGN: Electromyographic activity of the masseter muscles and anterior temporalis muscles was recorded bilaterally in different mandibular positions using bipolar surface electrodes. RESULTS: Compared to noncleft controls, patients with UCLP demonstrated (1) higher activation levels of masseter and temporalis muscles in the rest position, (2) lower potential function of masseter and temporalis, (3) inharmonious activity of the masticatory muscles during mandibular border movement, (4) a higher asymmetry index of the masseter and temporalis muscles, and (5) longer silent periods of the two muscles. CONCLUSIONS: The function of masticatory muscles is different in patients with UCLP with anterior crossbite. Muscle function should be considered when evaluating cleft patients for orthodontic treatment and orthognathic surgery.

Action Potentials↗