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At least 1,225 records · Page 68Linked to original sources
PubMed1979

Jaw muscle silent periods before and after rapid palatal expansion.

1. The electromyographic silent period was observed in jaw-closing muscles during a maximal clench following a tap to the mandibular symphysis in eight subjects before and after rapid palatal expansion. 2. No differences in mean silent period duration were observed among the three jaw-closing muscles examined. 3. A large (r = 0.96) and statistically significant (p less than 0.01) correlation coefficient between two sets of silent period durations at one session indicates that these measurements are repeatable and reliable. 4. The mean silent period duration for the eight patients with malocclusions was 33.5 msec. prior to rapid palatal expansion and 51.2 msec. after the completion of palatal expansion. The difference was statistically significant (p less than 0.01) and represents a 61 percent increase. 5. Patients with symptoms of TMJ dysfunction are not the only group showing a prolonged silent period duration.

Adolescent↗
PubMed1980

Biomechanics of differences in lower facial height.

A two-dimensional model which allows calculation of mechanical advantage of the human temporalis and masseter muscles is presented. The model is manipulated to demonstrate how selected differences in facial morphology affect the mechanical advantage of the muscles. The model is then used to evaluate the differences in mechanical advantage between patients with the long face syndrome and those with the short face syndrome. Differences in facial morphology between these two groups result in significant differences in the mechanical advantages of their muscles. Mechanical advantage may, in part, explain observed differences in bite force between the two groups. The model suggests that some surgical procedures used to correct facial disharmonies may have a significant effect on the mechanical advantage of the jaw muscles.

Adolescent↗
PubMed1989

Single motor unit and surface electromyogram analysis of human jaw-closing muscle reflexes after tapping an upper tooth.

The mechanical stimulation of an upper tooth elicited reflex responses in masseter and temporalis motor units, which were recorded with both surface and needle electromyograms (EMGs) simultaneously. The subjects maintained one of the recorded motor units, which was the latest recruited unit, at a constant firing frequency, varying from 12 to 25 Hz. After a latency of 10 ms, all 19 motor units were inhibited for a period, the duration of which depended on the prestimulus firing frequency. A motor unit with a low firing frequency was inhibited for a longer time than a faster firing one. At the end of this inhibition there was an increased probability of firing recorded, in the form of a time-locked clustering of action potentials. Furthermore, in three motor units, all firing at a frequency of about 25 Hz, the first interspike interval after the inhibition was regularly half the duration of the mean prestimulus interspike interval. The timing of the last action potential before the stimulus influenced significantly the reflex responses in all motor units.

Action Potentials↗
PubMed1992

The use of transcranial stimulation in the fabrication of an occlusal splint.

An alternative method for fabricating occlusal splints by means of electric transcortical stimulation is presented. Ensuing results in one patient suggest neuromuscular benefits. However, the centric occlusal position determined by this method is a painful procedure because of electric stimulation on the scalp. Further and extensive investigations must be carried out to assess the clinical benefits and limits of this method.

Dental Occlusion↗
PubMed1982

Trigeminal neuralgia as a consequence of circulatory disorders in the infratemporal and pterygopalatine fossae.

An extensive review of the well documented experimental and clinical findings related to trigeminal neuralgia shows, that it is possible to set up an unifying theory for trigeminal neuralgia, which would explain most clinical features of the disease and also would be congruent with several other theories that have previously been presented. Thus, trigeminal neuralgia is proposed to be the result of a combination of predisposing anatomical variations, impaired arterial and venous circulation, and morphological changes in the infratemporal fossa and cavum Meckeli. The process is initiated by disturbances of dental occlusion and mandibular function, resulting in muscular hypertrophy, which finally leads to increased perineural pressure and hypoxia in the nervous tissue. Through a series of related events this results in massive afferent discharges in the trigeminal nerve, which are strong enough to break through an inhibitory gating mechanism in the nucleus caudalis, and which are experienced by the patient as a pain attack. But the tissue hypoxia, which partly has elicited the pain, will finally also be the critically delimiting factor for further signal transmission, thereby stopping the pain attack.

Humans↗
PubMed2004

Maximal bite forces in healthy young adults as predicted by surface electromyography.

OBJECTIVES: To assess the repeatability of maximal bite force estimates as obtained by submaximal electromyographic-force relationships performed simultaneously and symmetrically in both sides of the mouth. The protocol could be used in a clinical context to obtain indicative values for the occlusal loads to be resisted by the prosthetic reconstructions. METHODS: Ten young healthy subjects performed; (1) a maximum voluntary clench (MVC) directly on their occlusal surfaces; (2) four simultaneous recording of submaximal bite forces (98, 196, 304 and 392 N on two transducers positioned on the left and right first mandibular molars) and surface EMG potentials of the masseter and temporalis anterior muscles. The actual force peak value was recorded. For each subject, a linear regression was run between the simultaneous bite force and EMG submaximal values recorded in the four tests. Using the EMG potentials obtained during the MVC tests, the best fitting line was used to estimate a maximum bite force. Two independent recordings were made by each subject (2 week interval) and analyzed by correlation analysis, paired Student's t-test, and Dahlberg statistic. RESULTS: Significant linear relationships were found between bite force and EMG potentials (p<0.01). The two series of indirect estimates of maximal bite force were correlated (r=0.626) without systematic differences (Student's t, p>0.01). Dahlberg statistic was 115.37 N (approximately 36% of the total variance of the group). CONCLUSIONS: Simultaneously recorded submaximal bite forces and surface EMG potentials of mandibular elevator muscles had a linear relationship. The estimates of maximum bite force were repeatable on a short-term basis (2 weeks). The method limited the disadvantages of bite force recordings, and it could be used to obtain indicative values for the occlusal loads to be resisted by the prosthetic reconstructions.

Adult↗
PubMed1996

Adaptations of masticatory muscles to a hyperpropulsive appliance in the rat.

The plasticity of masticatory muscles was studied by comparing rats that were wearing a protrusive appliance and were kept on a liquid diet with two control groups: (1) pair-fed rats and (2) rats that had free access to ordinary pelleted food. The animals were 45 days old at the beginning of the experiment and were studied for a period of 20 days. Three jaw muscles with different functions were examined: masseter, temporalis, and digastric. Muscle fiber composition was determined (1) by fiber counting after staining with four monoclonal antibodies, which were able to recognize the four major myosin heavy chain (MHC) isoforms and therefore four fiber types (I, IIA, IIX, IIB) and (2) by electrophoresis on 6% polyacrylamide gels. The comparison between free-diet rats and pair-fed rats showed that the change from a hard pelleted diet to a liquid diet caused a shift in fiber type and MHC distribution, characterized by an increase of IIB MHC in temporalis and digastric muscles but not in the masseter muscle. The comparison between pair-fed rats and rats wearing appliances showed on the contrary a decrease in IIB MHC and an increase in IIA and IIX MHC. The results support the conclusions that (1) rat jaw muscles can quickly adapt to functional demand changing their fiber type composition, (2) the changes appear restricted inside the fast fiber population, and (3) fiber-type changes caused by dietary variation are not less than those caused by orthodontic intervention and must be taken into account to assess the effect of the appliance correctly.

Adaptation, Physiological↗
PubMed1995

Statistical analysis of differential lissajous EMG from normal occlusion and Class III malocclusion.

The method of differential lissajous electromyography (DL-EMG) was applied to investigate the relationship among the integrated EMG activity, timing, and coordination of the bilateral superficial anterior temporal and masseter muscle activities in normal occlusion and Class III malocclusion subjects. In both Class III malocclusion and normal occlusion subjects, the working side muscles showed a higher mean cumulative voltage (MCV) and mean maximum peak voltage (MMPV) compared with the balancing side. In addition, a higher MCV and MMPV of the working side masseter was observed in the normal occlusion group compared with that seen in the Class III group during both right and left side chewing (p < 0.01). Discriminant analysis applied to examine the distribution, the size and the shape of DL-EMG pattern further indicated a statistical difference between subject groups (p < 0.01). Finally, there was a significantly higher percentage of clockwise DL-EMG pattern-generation in the normal group compared with that seen for Class III subjects (p < 0.01). These data indicate that, compared with normal subjects, patients with a Class III malocclusion have a demonstrably abnormal masticatory muscle balance which is well characterized by the DL-EMG method.

Adolescent↗
PubMed1998

Detection of onset and termination of muscle activity in surface electromyograms.

A method of automated detection of onset and termination of rhythmic muscle activity in electromyograms (EMGs) is presented. A threshold level in the EMG is computed, such that amplitudes in the EMG signal exceeding this level indicate muscle activity. The threshold level is determined using a statistical criterion based on the amplitude distribution of the entire EMG signal. The working of the method is illustrated with EMG signals recorded from chewing muscles. EMG signals with a good as well as a worse signal-to-noise ratio are presented. The method can be used for any EMG signal containing cyclic bursts of activity and thus may be applied in studies on rhythmic movements, such as chewing, walking and breathing. An automated method of EMG burst detection has the advantage that large amounts of EMG data can be easily and objectively processed.

Electromyography↗
PubMed2002

Temporomandibular joint and masticatory muscle involvement in myotonic dystrophy: a study by magnetic resonance imaging.

OBJECTIVE: The purpose of this study was to evaluate the masticatory muscles and the temporomandibular joint (TMJ) by magnetic resonance imaging (MRI) in myotonic dystrophy (MD) patients. STUDY DESIGN: MRI of the masticatory muscles and TMJ was performed in 15 MD patients, 11 male and 4 female, aged 16 to 53 years (mean, 31 years). Many of them had dental malocclusion, especially Angle class III and anterior open bite, and 3 complained of recurrent TMJ dislocation. TMJ and masticatory muscle pain was not observed, and joint sounds were noted in only 1 patient. RESULTS: The analysis of MRI scans showed masticatory muscle involvement in 13 patients (86.6%). In 11, the involvement was moderate to intense. The main abnormalities observed were increased intramuscular tissue signal on T1 (fatty infiltration) and volumetric reduction of muscles. Regarding the TMJ, articular disk displacement was seen in only 1 patient, but abnormalities of disk shape were common. Mild bone abnormalities were frequently observed, including changes of shape and contour of bone surface, and sclerosis of bone marrow. In 4 patients the condyle moved anterior to the eminence with the mouth opened fully (condylar hyperexcursion). CONCLUSIONS: This study shows that masticatory muscles are frequently and intensively affected in MD patients. Bone changes are the most consistent abnormalities observed in the TMJ. It is possible that remodeling is caused by biomechanical changes in the jaw as a result of masticatory muscle involvement.

Adipose Tissue↗
PubMed1997

The role of the lateral pterygoid muscles in TMJ disorders during static conditions.

Intramuscular EMG of the lateral pterygoid muscles (LPM), surface EMG of the temporalis and masseter muscles and force measurements of the temporomandibular joint (TMJ) were synchronously used to investigate the biomechanical role of the two heads of the LPM in relation to internal derangement (ID) of the TMJ. EMG and kinetic analysis of five static conditions (resting, protraction, opening, molar and incisor clenching) and three maximum isometric masticatory forces (opening, molar and incisor clenching) were done to compare forces and muscular activity between TMJ ID and control subjects. The analysis of variance results of the integrated linear envelope (LE) EMG showed no significant differences between the two groups for the masseter and temporalis muscles. Therefore, there is no apparent reason to believe that these muscles are hyperactive in TMJ ID. The integrated LE EMG of the SLP was significantly lower in the TMJ group during molar clenching (104 microV + 60.0 over 159 microV + 68.8 for a p = .020). The superior head of the lateral pterygoid muscle (SLP) seemed to have lost its diskal stabilizing function. The integrated LE EMG signals of the ILP were significantly higher in the TMJ ID group during rest, resisted protraction and incisor clenching (p = .029, p = .046, p = .031 respectively). The ILP muscle has probably adapted to control the inner joint instability while continuing its own actions. The ILP muscle seemed to have lost its functional specificity. The results of the isometric forces showed that TMJ ID subjects exhibited significantly lower molar bite forces (297.1N over 419N, p = .042) confirming that they have less muscle strength and tissue tolerance than subjects with healthy masticatory muscle systems. A neuromuscular adaptation could be occurring in the TMJ ID masticatory system affecting muscular actions and forces.

Adaptation, Physiological↗
PubMed2001

Bite force in pre-orthodontic children with unilateral crossbite.

In the present study bite force was examined in pre-orthodontic children with unilateral posterior crossbite and compared with an age- and sex-matched control group. The sample comprised 52 children aged 7-13 years, 26 pre-orthodontic children with unilateral posterior crossbite (crossbite group), and 26 children with neutral occlusion (control group). Unilateral bite force was measured at the first molar by means of a pressure transducer. Furthermore, symptoms and signs of temporomandibular disorders (TMD) and number of teeth in contact in the intercuspal position (ICP) were recorded. In both groups, the maximum bite force increased significantly with age and with increasing stages of dental eruption, but the bite force in both sexes did not differ significantly. There were no significant differences in bite force between sides, but this was significantly smaller in the crossbite group than in the controls (P < 0.001). Regression analysis showed that stage of dental eruption (P < 0.001), number of teeth in occlusal contact (P < 0.01), and unilateral crossbite (P < 0.001) were the only variables significantly correlated with bite force. The number of teeth in contact was significantly smaller in the crossbite group than in the controls (P < 0.05) and the frequency of muscle tenderness was significantly higher in the crossbite group than in the controls (P < 0.05). These results suggest that differences in the muscle function associated with unilateral crossbite lead to a significantly smaller bite force in the crossbite group compared with controls and this difference did not diminish with age and development. These findings indicate that early treatment of unilateral posterior crossbite is advisable to optimize conditions for function.

Adolescent↗