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At least 721 records · Page 40Linked to original sources
PubMed2000

Bone surface strains and internal bony pressures at the jaw joint of the miniature pig during masticatory muscle contraction.

The long-standing debate on whether the jaw joint is loaded is due in part to the complexity of the factors involved, including a number of different muscles, each with a potentially unique role. This study sought to elucidate how two major jaw muscles, the masseter and the lateral pterygoid, influence jaw-joint loading. Twenty-five 10-month-old miniature pigs were divided into two groups, controls and pigs with the lateral capsular ligament of the jaw joint stripped surgically; this was expected to affect loading by destabilizing the joint. Rosette strain gauges were bonded to: (1) the lateral surface of the squamosal bone (equivalent to the squamosal portion of the temporal bone in humans) at the level of the articular eminence; (2) the lateral surface of the condylar neck; and (3) the lateral surface of the mandibular corpus below the molar region. Semiconductor pressure transducers were placed underneath the surfaces of the anterior slope of the condyle and the posterior slope of the articular eminence through drilled holes. Strains and internal bony pressures were recorded during stimulated tetanic contractions of the masseter or lateral pterygoid muscles. Masseter contraction, either alone or with the contralateral muscle, caused net tension in the squamosal bone and net compression in the condylar neck. The orientations were approximately vertical to the occlusal plane. Masseter contraction elevated both the condylar and eminence pressures from their resting values. The strains caused by lateral pterygoid contractions were much smaller than for the masseter with the exception of the condylar location. Ipsilateral lateral pterygoid contraction decreased both the condylar and eminence pressures from their resting values, perhaps because condylar movement altered the contact between the joint surfaces. Surgical disruption enhanced both pressure changes and bone strains under either muscle contraction but their overall patterns were not altered. In conclusion, both strains and pressures in the jaw joint varied according to specific muscle activity.

Analysis of Variance↗
PubMed1996

Masticatory muscle symptoms in a patient with McArdle's disease.

Myofascial pain dysfunction syndrome is a syndrome characterized by chronic preauricular pain and tenderness involving the muscles of mastication. The cause is often multifaceted and generally poorly defined. A case of McArdle's disease is discussed in which the patient presented with symptoms consistent with myofascial pain dysfunction syndrome. McArdle's disease is a rare autosomal recessive glycogen storage disorder in which there is a metabolic myopathy that results in exercise intolerance, muscle pain, and tenderness, and that in this patient gave rise to chronic symptoms of myofascial pain. Although uncommon, McArdle's disease should be considered in the diagnosis of patients with symptoms of myofascial pain dysfunction syndrome because the condition has important implications with respect to the patients renal function and because it can be readily distinguished by simple investigations.

Adult↗
PubMed2002

Variation in masticatory muscle activity during subsequent, submaximal clenching efforts.

In previous studies to the relative contribution of the jaw closing muscles to the maintenance of submaximal clenching levels, a considerable variation in the electromyography (EMG) activities of these muscles during subsequent efforts was found. In this study, it was examined to what extent this variation could be explained by coincidental variations in mandibular positioning. From seven healthy individuals, a total of 90 EMG sweeps was recorded: three conditions (intercuspal position and two types of stabilization appliances) x three clenching levels (10, 30 and 50% of maximum voluntary contraction level) x 10 repetitions. Mandibular position was monitored with a six degrees of freedom opto-electronic jaw movement recording system. Variations in mandibular positioning during subsequent, submaximal clenching efforts explained up to 25% of the variance in the indices that quantify the relative contribution of the jaw closing muscles to the total clenching effort (P=0.000; ANOVA). Only a weak dependency of positioning upon clenching condition was found whereas during higher clenching levels, the positioning effect tended to be smaller than during lower levels. In conclusion small, coincidental variations in mandibular positioning during subsequent clenching efforts partly explain the variance in EMG activity of jaw closing muscles, especially at lower clenching levels.

Adult↗
PubMed2002

Immediate effect of a stabilization splint on masticatory muscle activity in temporomandibular disorder patients.

Surface electromyography (EMG) allows the quantification of the occlusal equilibrium in dysfunctional patients, for instance in those with temporomandibular disorders (TMD). Fourteen patients (ten women, four men) with internal derangement type I were selected among the TMD patients referred to a private practice in Milan. A stabilization splint with posterior contacts was made for each patient. To verify the static neuromuscular equilibrium of occlusion, EMG activity of left and right temporal and masseter muscles was recorded in all patients and the activity (ratio between the activities of the temporal and masseter muscles) index was computed over a maximum voluntary clench test of 3 s. Muscular waveforms were also analysed by computing a percentage overlapping coefficient (POC, an index of the symmetric distribution of the muscular activity determined by the occlusion). The total electrical activity was measured by calculating the area under the entire muscular waveforms. In all patients EMG was performed just before and immediately after the insertion of the splint and data were compared by paired Student's t-tests. Overall, the splint reduced the electrical activity of the analysed muscles (P < 0.005) and made it more equilibrated both between the left and right side (larger symmetry in the masseter muscle POC, P < 0.05) and between the temporal and masseter muscles (activity index, P < 0.01).

Adult↗
PubMed1999

The effects of a single intercuspal interference on electromyographic characteristics of human masticatory muscles during maximal voluntary teeth clenching.

In 13 healthy subjects (eight men and five women, mean age, 22 years), an aluminum intercuspal interference (height, 0.25 mm) was placed on the maxillary right first premolar to study its effect on the contractile symmetry of the right and left masseter and anterior temporalis muscles when measured through a Percentage Overlapping Coefficient (POC), derived from surface electromyographic recordings of maximum voluntary teeth clenching. Additionally, and to estimate the potential of the experimental intercuspal interference to induce lateral displacement of the mandible, a Torque Coefficient (TC) was derived from surface electromyographic recordings. The conclusion was that the experimental occlusal interference gave rise to asymmetric contractile activity in the studied mandibular elevator muscles as well as a potential to displace the mandible in a lateral direction.

Adult↗
PubMed2005

Post-traumatic severe trismus caused by impairment of the masticatory muscle.

Restriction of the mouth opening from a pathologic condition outside the temporomandibular joint is called a pseudo- or extra-articular ankylosis. The authors report two cases of severe post-traumatic pseudoankylosis. One case showed fibrous degeneration of the bilateral masseter muscles without a facial bone fracture, which caused severe trismus, a mouth opening of less than 2 mm, and gradually appeared after blunt injuries to the face. The other was a rare case accompanied with the bone formation in the masseter muscle and was diagnosed as myositis ossificans traumatica, which also presented as severe trismus, with a maximal mouth opening of 5 mm after facial violence. Both were surgically treated with dissection of the affected muscles. In addition, a hemicoronoidotomy was performed in the case of myositis ossificans traumatica. Although a conservative therapy with physical rehabilitation is the basic policy for the management of pseudoankylosis of the temporomandibular joint, a surgical treatment should be considered when the origin of the problems is an osteogenic character or severe extra-articular ankylosis resistant to conservative therapy before completion of true temporomandibular joint ankylosis.

Adolescent↗
PubMed1991

Chewing and swallowing activity of masticatory muscles in patients with a complete upper and a partial lower denture.

The chewing and swallowing activity of jaw-closing muscles was studied longitudinally in 30 partially edentulous subjects who were provided with an immediate complete upper and a partial lower denture. Electromyographic recordings of the anterior temporal and masseter muscles were obtained during habitual chewing of apple and during swallowing of saliva and water, before final extractions and 7 weeks, 6 months, 1 year and 2 years after denture insertion. At the pre-treatment stage, when the patients were chewing with a residual anterior dentition, the mean voltages showed low values compared to findings reported in subjects with a complete natural dentition. After 6 months of denture use, the chewing forces showed significant increases in amplitude, and the increased force of contraction persisted to the 2-year stage. The recordings of swallowing revealed no significant changes in maximal mean voltage during the observation period. However, there was a significant increase in the duration of the swallows after 1 year of denture wearing, which might be related to stabilization of the complete upper denture due to continuing resorption of the maxillary ridge.

Adult↗
PubMed2002

Effect of sustained contraction on motor unit action potentials and EMG power spectrum of human masticatory muscles.

The sequelae of a sustained clench are incompletely understood. Our experimental questions were to compare the responses of men and women, to compare masseter and anterior temporalis muscles, and to test hypotheses for the reduction of the median frequency of power spectra. We recorded duration, amplitude, number of phases, and area of the motor unit action potential before and after a sustained clench and the median frequency of the electromyographic power spectrum in 41 subjects. After the clench, the median frequency was lower, the action potential duration longer, the number of phases increased, and the area larger, but the amplitude was not different. Males and females failed to differ. Compared with the temporalis, the masseter had a lower median frequency, longer duration, larger number of phases, and increased area. Our results are consistent with a decrease in the conduction velocity of the muscle action potential as an explanation of the spectral shift.

Action Potentials↗
PubMed1998

Examination of nerve distribution to masticatory muscles using a silicone permeation technique.

The detailed anatomical distribution of nerves throughout the human body has generally been studied by dissection of fixed cadavers in liquid. In this traditional method, it is difficult to maintain the position of nerves on their respective muscles. It is also difficult to keep the distributed form of the nerves. To understand the morphology of nerves, it is essential to determine their location and distribution precisely. In this study the masseter muscle was removed from a cadaver after fixation with formalin. The muscle was then permeated with silicone using the following procedure. The muscle fixed by 10% formalin was dehydrated with alcohol. After dehydration, alcohol was replaced with methylene chloride. The sample was permeated by silicone in a permeater. Following dissection, enamel was applied to the nerve by hand to fix its position. This new permeation method provided excellent localization of nerves innervating the muscle and has the added advantage of providing a three-dimensional structure of neural anatomy similar to the casting procedures used to visualize blood vessels.

Diffusion↗
PubMedDate not supplied

Effect of resilient liners on masticatory muscle activity of edentulous patients: clinical and electromyography studies.

This investigation evaluated how the soft lining of both maxillary and mandibular complete dentures influences the activity of the masseter and temporalis muscles. Electromyography was used to determine changes in muscle activity. The findings, expressed by Root Mean Square values, indicated an increase in muscle activity after insertion of dentures and prior to application of soft lining material. These activities decreased gradually throughout the 12-week evaluation period following the application of soft liner. Significant differences were noted between masseter and temporalis muscle activity during mastication of different types of food.

Analysis of Variance↗
PubMed1995

[A study of the relationship between electromyographic activity of the masticatory muscles and the variations of the occlusal vertical dimension for edentulous subjects]

The study was performed in fifteen edentulous subjects with the EMG activity were recorded at the varying occlusal vertical dimension maintaining constant bite force value of 4kg.The results showed that maintaining constant bite force the amplitudes of EMG activity of the anterior temporal and masseter muscles are decreased with increasing the occlusal vertical dimension and correlation relation between them,that there is a stable region about 1.0mm for the anterior temporal muscle and about 1.5mm for the masseter muscle during the changes in electrical activity.It is represent that there is a physiological region of the occlusal vertical dimension for edentulous patient.

Journal Article↗