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Results for “Masticatory Muscles”

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PubMed1991

Application of magnetic resonance imaging and ultrasonography to preoperative evaluation of masseteric hypertrophy.

A case of unilateral masseteric hypertrophy in a 30-year-old man is described. Preoperative evaluation was performed by magnetic resonance imaging (MRI), computed tomography (CT) and ultrasonography (USG). MRI could delineate not only the border between medial and lateral layers of the masseter but also delineate the hypertrophic portion. MRI also provided more information in respect of the masseter muscle as well as the other masticatory muscles and the surrounding tissues than CT. USG was useful because of its real-time processing, especially in this case where facial asymmetry was emphasized during mastication. We resected the medial lower-half of the masseter intraorally based on these imagings and obtained a successful result.

Adult↗

PubMed1999

Nocturnal masseter EMG activity of healthy subjects in a natural environment.

Facial pain of patients with craniomandibular disorders might be caused by muscle overload. However, the activity of masticatory muscles of healthy individuals is still unknown. The aim of this study was therefore a first attempt to clarify this question by recording the masseter muscle activity of healthy subjects during sleep by means of portable recorders. The study was performed on 21 healthy subjects selected after telephone and questionnaire screenings and clinical examination from among randomly selected inhabitants of Zürich. The masseter EMG was recorded during seven nights in each subject's natural environment with the electrodes in reproducible position. The signal was analyzed for number, amplitude, and duration of contraction periods defined as signal portions above a threshold which could contain sub-threshold signal portions shorter than the standby time of 5 sec. The signal amplitude was expressed in percent of the amplitude recorded during maximum voluntary clenches (%MVC). An average of 71.9 +/- 28.7 contraction episodes per night (men, 74.7 +/- 30.1; women, 65.0 +/- 23.8; p = 0.043), i.e., of 10.5 +/- 3.8 per hour (men, 11.0 +/- 4.0; women, 9.3 +/- 3.0; p = 0.005), was found. The average mean amplitude was 26.2 +/- 6.4% MVC (men, 27.0 +/- 6.8; women, 24.4 +/- 4.5; p = 0.009). The duration of the episodes had a mode of 0.5 sec, and the group mean of the integral of the amplitude over time was 123.7 +/- 157.9% MVC (men, 138.9 +/- 184.0; women, 85.9 +/- 28.2; p = 0.005). Healthy subjects showed intermittent periods of masseter activity during sleep which, on average, were of rather low intensity and short duration.

Adult↗

PubMedDate not supplied

[Arthromuscular interrelations in TMJ functional pathology].

TMJ disorders includes: TMJ and masticatory muscles, pain, joint sounds, deviation and limitation of mandibular movements. A critical analysis of the literature dealing with the relationship between joint and muscle disorders in other joints (knee), leads to evaluate the reliability of the hypothesis of the existence of an arthro-myogenous relation in the aetiopathogenesis of craniomandibular disorders. As a preliminary conclusion we can say that the joint derangement seems the primary factor in the pathogenesis of TMJ disorders and cannot to differentiate muscle from joint involvement seems a difficult task.

Electromyography↗

PubMed2006

Dynamic mechanics in the pig mandibular symphysis.

During mastication, various biomechanical events occur at the mammalian jaw symphysis. Previously, these events have been studied in the static environment, or by direct recording of surface bone strains. Thus far, however, it has not been possible to demonstrate directly the forces and torques passing through the symphysis in association with dynamically changing muscle tensions. Therefore, we modified a previously published dynamic pig jaw model to predict the forces and torques at the symphysis, and related these to simulated masticatory muscle tensions, and bite, joint and food bolus forces. An artificial rigid joint was modelled at the symphysis, allowing measurements of the tri-axial forces and torques passing through it. The model successfully confirmed three previously postulated loading patterns at the symphysis. Dorsoventral shear occurred when the lower teeth hit the artificial food bolus. It was associated with balancing-side jaw adductor forces, and reaction forces from the working-side bite point. Medial transverse bending occurred during jaw opening, and was associated with bilateral tensions in the lateral pterygoid. Lateral transverse bending (wishboning) occurred at the late stage of the power stroke, and was associated with the actions of the deep and superficial masseters. The largest predicted force was dorsoventral shear force, and the largest torque was a 'wishboning' torque about the superoinferior axis. We suggest that dynamic modelling offers a new and powerful method for studying jaw biomechanics, especially when the parameters involved are difficult or impossible to measure in vivo.

Animals↗

PubMed1999

Origin of primary sensory neurons innervating the buccal stretch receptor.

The primary sensory neurons innervating mechanoreceptors in oro-facial regions have their cell bodies in either the trigeminal ganglion or the mesencephalic nucleus of the trigeminal nerve. The buccal stretch receptor (BSR), a type of mechanoreceptor in the jaw of rodents, has recently been recognized as signaling the position of the mandible. The location of the primary afferent neurons innervating this receptor is unknown. To investigate the cell bodies of the BSR afferent neurons in rats, we applied wheat germ agglutinin-horseradish peroxidase (WGA-HRP) to the proximal stump of the severed nerve branch of the buccal nerve that supplied the BSR. HRP-labeled cell bodies were observed in the posterolateral portion of the ipsilateral trigeminal ganglion. None was found in the contralateral trigeminal ganglion or in the brainstem. All labeled cell bodies were oval or round and closely resembled pseudo-unipolar neurons. The mean diameter of the labeled somata ranged between 25.5 and 52.5 microm, with small (< or = 30 microm), medium (from 31 to 40 microm), and large somata (> or = 41 microm) accounting for 8.8%, 54.9%, and 36.3%, respectively. Among the myelinated nerve fibers in the branch in which WGA-HRP was applied, 78.5% terminated in the BSR and had larger fiber diameters than the rest, indicating that most of the medium and large HRP-labeled cell bodies were BSR afferents. From these results and the ontogenetic origin of this receptor, it is suggested that the BSR differentiated from the mechanoreceptors in the oral mucosa or the fascia of masticatory muscles.

Animals↗

PubMed1979

Electromyography after lateral pterygoid myotomy in monkeys.

Neuromuscular patterns of five female rhesus monkeys (Macaca mulatta) were studied to determine the effect of laternal pterygoid myotomy on the function of selected groups of masticatory muscles. Activity characteristics of the lateral pterygoid muscle were recorded as early as four days postoperatively. By the end of the second postoperative month, bilateral lateral pterygoid muscle activity was demonstrated in all animals. In all cases, it closely resembled preoperative patterns of lateral pterygoid muscle function. The activity was observed regardless of whether an inert barrier was used to prevent reattachment of the muscle. The results of this study indicate that the lateral pterygoid myotomy does not have a long-term effect of inhibiting the function of the lateral pterygoid muscle.

Animals↗

PubMed1990

[Kinematics and dynamics of the temporomandibular joint and of the movements of the mandible].

In order to analyze the complicated movements of the mandible as the open-closing movement and the protrusio are, it is useful to evaluate the basic kinematic principles and reduce them to simple technical constructions. Both the open-closing movement and the protrusio could be reduced to 4-bar links, which were used to simulate the movements with help of a computer. Besides, the polodes and the curves of points in the muscular attachments could be constructed. The 2 entirely different 4-bar links have 3 things in common: The resting system - cranium, the moving system - mandibula, and 1 of the 2 arms connecting these 2 systems - the ligamentum laterale. As this ligament is taut during movements it can be considered a "guiding ligament" representing 1 of the 3 determining components of the mandibular movements. The other of the 2 arms has no anatomical equivalent; this arm, however, is "replaced" by the 2 other determining components of the mandibular movements: the joint and the muscles. The curves, which the Caput mandibulae describes, are practically identical for the open-closing movement and the protrusio despite of the different 4-bar links and these curves exactly correspond to the Discus articularis, taut by the upper part of the M. pterygoideus lateralis. The muscles do not only just move the mandibula, but they are also the component, which can choose between the different mandibular movements. By means of the curves, which points in the muscular attachments describe, the function of the masticatory muscles could be analyzed exactly.

Computer Simulation↗

PubMed1982

[Role of the lateral pterygoid muscle in mandibular movements].

The two bundles, superior and inferior, of the lateral pterygoid muscle were studied by EMG and integrated EMG during various movements of the mandible in 36 children and 2 adults. At the same time, the EMG of other masticatory muscles was also recorded. The functional specialization of the two bundles is expressed by different levels of recruitment: In the inferior bundle (pterygo-condylian,) electrical activity is stronger in the movements of opening, antepulsion and controlaterality. In the superior bundle (spheno-meniscal), activity is stronger in the movements of occlusion and retraction. Thus the inferior bundle principally has a function of stabilization of the temporomandibular joint.

Adolescent↗

PubMed1983

Muscular rehabilitation after orthognathic surgery.

There is both a biologic and a clinical foundation for the use of therapeutic exercise after othognathic surgical procedures to restore normal function of the jaw muscles. This can be accomplished by a systematic plan Of occlusal and muscular rehabilitation after release of maxillomandibular fixation. Through the diligent application of physical therapy principles, the function of the masticatory muscles can be more efficiently rehabilitated after orthognathic surgery and maxillomandibular fixation.

Dental Occlusion↗

PubMed1991

Interspecific perspective on mechanical and nonmechanical models of primate circumorbital morphology.

Linear dimensions and angular orientations of the browridge, postorbital bar, and postorbital septum were obtained from a representative series of primates and compared with variables associated with several nonmechanical and biomechanical/mechanical models put forward to explain the form and function of the circumorbital region. Analyses of the results indicate that face size is the primary determinant of variation in primate circumorbital morphology. Anteroposterior browridge thickness is correlated with neural-orbital disjunction among anthropoid primates, but not among prosimians. This difference appears related to differences in the construction of the upper face and anterior cranial fossa between prosimians and anthropoids. Little support is demonstrated for the anterior dental loading model of browridge development. Mediolateral postorbital bar width and (to a lesser degree) browridge height are correlated with neurofacial torsion during mastication and variation in masticatory muscle size. These analyses further suggest that since circumorbital structures (especially the browridges) are located the farthest away from the chewing apparatus, they are least affected by masticatory stresses.

Animals↗

PubMed1976

Trismus resulting from central nervous system lesion.

Three cases of unusual trismus are reported, occurring in patients with lesions of the central nervous system. On the basis of the clinical and electromyographical findings and observation of the course of the trismus this is interpreted as a symptom of a lesion of the brain stem, causing a dis-synergism of the masticatory muscles.

Accidents, Traffic↗

PubMed2002

Masticatory performance in patients with anterior disk displacement without reduction in comparison with symptom-free volunteers.

Masticatory function can be impaired by craniomandibular disorders. The aim of this study was to assess masticatory performance in patients with an anterior disc displacement (ADD) without reduction. In the experiments, 29 patients and 33 age- and gender-matched volunteers chewed artificial test food for 60 chewing strokes. The collected remains of the test food were filtered, dried, fractionated by a sieving procedure, and weighed. The particle size distribution was then described using a cumulative distribution function. Patients and controls were clinically examined, and patients were asked to complete a pain questionnaire. Comparison with controls, patients showed significantly reduced masticatory performance. Patients that had had a disorder longer than 3 yr tended to display less reduction of their masticatory performance. Neither the treatment methods used, nor restriction of daily life activities or pain intensity were significantly correlated with masticatory performance. Jaw mobility was significantly reduced in patients. More than half of the patients and none of the controls had joint noises and trigger points in the masticatory muscles. Pain was present, in particular, during chewing and maximal opening of the mouth. It was concluded that patients with ADD without reduction have a significantly reduced masticatory performance.

Activities of Daily Living↗

PubMed1989

Lack of correlation between mouth-breathing and bite force.

The correlation between mouth-breathing and bite force was studied in 81 children, 7 to 16 years old. Mouth-breathing was diagnosed on the basis of the subject history, the rhinomanometrically determined nasal airflow and the size of the airway measured on the profile cephalogram. The maximum bite force was measured at the first molars. In addition, the facial morphology was analysed on profile cephalograms. Both mouth-breathing and bite force were associated with the facial morphology but there was no association between mouth-breathing and bite force. It was concluded that the long-face morphology characteristic of mouth-breathing children is not due to weak masticatory muscles.

Adolescent↗

PubMed1996

[Effects of lateral mandibular deviation on masseter muscle activity].

The investigation of the physiological response of masticatory muscle which is associated with the perception of the mandibular lateral deviation is clinically important. Therefore, the effects of various lateral mandibular deviation on the masseter muscle function were investigated on five healthy subjects. The mandibular position was deviated 0.5, 1.0, 1.5, 2.0 and 3.0 mm to the right and left from a reference position corresponding to the rest position. The mandible was passively retained in each test position by means of a bite block. Electromyographic activity (background activity) was recorded with bipolar surface electrodes applied to the right and left masseter muscles. Jaw-jerk reflex was evoked by a reflex hammer, and motoneuron activity was indirectly examined. The background activity as well as the amplitude of the jaw-jerk reflex on the mediotrusive side mainly increased in proportion to the mandibular deviation. However, most subjects showed no significant change about 3 mm from the reference position in the background activity and about 2 mm in the range of muscle activity evoked by the jaw-jerk reflex. These results suggested that the masseter jaw-jerk reflex may assist clinical examination of small mandibular deviations.

Adult↗

PubMed2005

[Influence of botulinum toxin on myogenous facial pain].

OBJECTIVE: Can chronic pain of the masticatory muscles be positively affected by low dose injection of botulinum toxin (BTX-A)? METHODS: Twenty patients suffering chronic myofacial pain were questioned and examined after injection of 25-50 U Dysport into the affected muscles over a period of 8 weeks. RESULTS: Four weeks after injection of BTX-A patients reported a significant reduction of pain (p <0.001, paired t-test. Power of performed test with alpha 0.050:1.000). Then the pain remained constant over the next 4 weeks. Concurrently a significant increase of mandubular range of movement was observed (p <0,05, Wilcoxon signed rank test). CONCLUSIONS: Even though lacking placebo control the findings suggest that patients suffering chronic myofacial pain may benefit from injection of low dose BTX-A into the affected muscles.

Adult↗

PubMed1998

Effects of dopaminergic drugs, occlusal disharmonies, and chronic stress on non-functional masticatory activity in the rat, assessed by incisal attrition.

Observational methods and the recording of nonspecific jaw movements or masticatory muscle activity have been used to evaluate oral parafunctional movements in animal models of bruxism. In this study, we have used a new approach in which the non-functional masticatory activity in the rat was assessed by the measurement of incisal attrition, with the aim of investigating the role of diverse factors involved in the etiology of bruxism. We quantified the attrition rate weekly by making superficial notches in the lower incisors and measuring the distances to the incisor edges. Repeated stimulation of the dopaminergic system with apomorphine led to an enhancement of the non-functional masticatory activity (p < 0.0001). The severity of the apomorphine-induced oral behavior was positively correlated (r(s) = 0.69, p < 0.01) with an increase in the incisal attrition rate (20.9%, p < 0.0001). Apomorphine-induced non-functional masticatory activity was strongly enhanced by the placement of an acrylic cap on both lower incisors (306%, p < 0.0001), but not by the cutting of a lower incisor. Repeated cocaine administration also increased the attrition rate (22.5%, p < 0.0001). However, neither chronic blockade of dopaminergic receptors with haloperidol, nor its withdrawal, modified attrition. In addition, since emotional disturbances are considered to be causal factors of bruxism, we tested whether experimental stress might accelerate tooth wear. Exposure to two different chronic stress regimes did not induce significant changes in incisal attrition. Moreover, exposure to chronic stress after the withdrawal of chronic haloperidol treatment did not alter attrition either. These results partially support the role of the central dopaminergic system in bruxism and suggest that stress, in general, may not be a relevant factor in tooth wear.

Analysis of Variance↗

PubMed2004

A revised view of the dynamics, physiology, and treatment of occlusion: a new paradigm.

A new perspective is proposed regarding the functional dynamics of occlusion, the masticatory muscles, and mandibular placement. Each is analyzed on the basis of a new criterion: force. Stomatognathic function is represented as an ongoing equilibrium maintained between the three-dimensional set of individual occlusal forces and the three-dimensional set of bilateral muscle forces. Mandibular placement is of prime importance, mediating as it does between the two. The conclusion is drawn that occlusion and the muscles can correlate optimally with each other only when the mandible occupies its neuromuscular position (NMP), herein defined as that placement where muscle accommodation is at its absolute minimum. The conclusion is that only the muscles themselves are capable of establishing the NMP and that customary conventional technology is inadequate. A new technology, hydrostatics, is needed to create the special (not existing naturally) occlusal conditions essential to optimally integrating occlusion, mandibular placement, and muscles. Preliminary EMG data is offered in support of this conclusion.

Bite Force↗

PubMed2000

Occlusion: what it is and what it is not.

Dental occlusion is much more than the physical contact of the biting surfaces of opposing teeth or their replacements. Occlusion is more comprehensively defined biologically as the coordinated functional interaction between the various cell populations forming the masticatory system as they differentiate, model, remodel, fail, and repair. Morphologic variations are very common and represent the norm. Even though the occlusal or musculoskeletal relationship may not meet the definition of the clinician's concept of an optimum or ideal occlusion, it must be appreciated that for that particular patient, the tissues of the masticatory system may have developed a stable, functional, healthy, and comfortable equilibrium. However, when the functional equilibrium is perturbed or when the occlusion is being re-established, specific treatment criteria are as important today, if not more important with the rapid growth of implant placements, as ever before. Treatment of the occlusion should be considered on an individual basis based on the specific physiologic needs of the various tissue systems within the masticatory system rather than on a preconceived, stereotyped or universal basis. It has long been established and recently proven that proper management of the occlusion is directly correlated to the successful treatment and maintenance of the teeth and, at times, the supporting tissues. On the other hand, it has not, to date, been scientifically proven that occlusion is directly correlated to the musculoskeletal disorders that affect the jaw (temporomandibular joint or masticatory muscle disorders).

Centric Relation↗