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At least 721 records · Page 40Linked to original sources
PubMed2002

Relationship between occlusion and EMG activity of the masseter muscles during clenching at maximal intercuspal position: a comparative study between prognathics and controls.

In the prognathic (P) patient group clenching at maximal intercuspal position (MIP), we found that the Ar-Go-Me angle is greater than in the control group (C = 120.9 degrees +/- 7 degrees vs. P = 134.4 degrees +/- 5.2 degrees): the same as the masseter fibers angle (alpha). The average EMG voltage class was similar in both groups (C = 1488.5 +/- 303.4 microvolt vs. P = 1317.6 +/- 293.4 microvolt). The mean total number of contact points in tooth arches was greater in the control group than in the patient group (C = 5.77 +/- 0.43 vs. P = 3.07 +/- 0.29), and there was a greater number of contact points between both premolar and molar areas. Both the control group and the patient group showed balanced occlusion in the premolar and molar areas. Therefore the finding of a similar mean EMG value between the control group and the patients emphasizes the importance of balanced contact points in the posterior areas.

Adult↗
PubMed1993

Activity of anterior temporalis and masseter muscles during deliberate unilateral mastication.

The reproducibility of electromyographic parameters descriptive of deliberate unilateral chewing (activity, timing, curve symmetry) was investigated in normal asymptomatic volunteers. The best time for the initiation of muscle activity was also examined, with the future aim of staging TMJ internal derangements. The results suggest that activity is the most reliable variable, indicating that it may be helpful in describing muscle incoordination. When time was used in conjunction with another variable, overall reproducibility decreased.

Adult↗
PubMed1992

Regional 31P magnetic resonance spectroscopy of exercising human masseter muscle.

Changes in fibre structure and function associated with exercise have been quantified ultrastructurally and biochemically in selected limb muscles, but the biochemical events associated with contraction are rarely studied in the human jaw muscles. Here, 31P NMR spectroscopy, or MRS, was used to examine the multipennate masseter in six adult men at rest and while performing isometric clenching exercises. NMR spectra were acquired from three locations within the muscle with a 2 x 3 cm, single-turn, copper receiver coil. The spectra, corrected for partial saturation effects, were quantified on the basis of relative peak area and position. The inorganic phosphate (Pi) to creatine phosphate (PCr) ratio (Pi/PCr), which has been shown to be indirectly related to the phosphate potential and hence the metabolic activity, as well as pH, were calculated for each site and exercise. The mean resting Pi/PCr ratio was greater for the deep part of the muscle than for the superficial and intermediate parts; these differences were significant to p less than 0.01. The mean pH was similar in all parts of the muscle at rest. During exercise, a significant increase in mean Pi/PCr was found in the superficial and intermediate parts of the muscle; both these differences were significant to p less than 0.05. An accompanying decrease in mean pH was observed in all parts of the muscle during exercise. In the superficial part, this decrease was significant to the p less than 0.05 level, and in the deep part, to the p less than 0.001 level. No significant differences were found for these measures between left and right molar clenching.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Estimation of blood flow by 133Xe clearance in human masseter muscle during rest, endurance of isometric contraction, and recovery.

Sixty-four measurements of 133Xe clearance from the masseters of 9 individuals, who had no facial or oral pain, were used to evaluate changes in intramuscular blood flow (IMBF) caused by endurance of isometric contraction at approx. 50 per cent of maximum voluntary EMG activity. On average, the IMBF during endurance increased by 4.2 times in 6 individuals and decreased 62 per cent of the rest flow in 3 individuals. Overall, the group average of endurance flow was 2.5 times higher than the initial rest flow. The group average of post-endurance hyperaemia was 27 times higher than the initial rest flow and 11 times higher than the endurance flow. IMBF during the final rest was 1.7 times higher than the initial rest flow. The relative IMBF during endurance was negatively correlated to muscle effort, and the post-endurance flow in relation to the endurance flow presented a compensatory positive correlation to the muscle effort. Although the average IMBF tended to increase during endurance, it was insufficient to meet the demand of the much higher relative increase in muscle activity, as indicated by the pronounced post-endurance hyperaemia, especially after long endurance.

Adult↗
PubMed1986

The influence of jaw position and antagonistic tooth relations on the appearance of a short-latency excitatory reflex in the human masseter muscles following mechanical tooth stimulation.

Post-stimulus electromyographic complexes (PSEC) were elicited by standardized tapping of a central upper incisor in 12 subjects during isometric voluntary biting in two positions, the incisor edge-to-edge (IEE) or the maximal occlusion (MO). In IEE a short latency excitatory peak (P wave) was present in the PSEC; this was absent in MO. By superimposing the rough EMG sweeps without full-wave rectification, it appeared that this P wave was brought about by synchronous masseter motor-unit firing.

Action Potentials↗
PubMed1981

[Electrical properties of membranes of motor neurons innervating the masseter muscle in rats].

Membrane resting and action potentials evoked by antidromic and direct stimulation were studied in neurons of the rat trigeminal motor nuclei. It is shown that in the given motor nuclei there are cell populations both with low and high membrane potentials. Motoneurons with high resting potentials were characterized by shorter latent period of antidromic activation, longer duration of spike and after depolarization and lower input resistance. Bimodal character of electrophysiological parameters distribution in the trigeminal motor nuclei show that "slow" and "fast" fibres of m. masseter may be innervated by different types of motoneurons.

Animals↗
PubMed2001

Colour Doppler sonographic analysis of blood-flow velocity in the human facial artery and changes in masseter muscle thickness during low-level static contraction.

Muscle oedema, which can be seen as a thickness increment by ultrasonography, is important in provoking pain and fatigue during low-level contraction. Although oedema is related to the balance of inflow and outflow of blood, there are no data on the correlation between muscle thickness change and blood-flow. Blood-flow velocities in the facial artery and the muscle thickness changes were measured by colour Doppler ultrasonography in 30 healthy volunteers during 20 min contraction with 10% of maximum force. Thickness and velocity changes both reached a peak in the initial phase of contraction. The initial change of thickness did not correlate with the velocity in the facial artery, while those immediately after exercise showed a high correlation. The velocity changes in the facial artery might depend on both the general response to contraction and local metabolic or mechanical factors in the contracted masseters.

Adolescent↗
PubMed1994

Motor-unit reflex inhibition in different regions of the human masseter muscle.

Regional localization of reflexes is common in anatomically complex limb muscles, but it is uncertain whether this occurs in the multipinnate human jaw-elevator muscles. In this study, motor-unit (MU) inhibitory reflex behaviour was examined in different regions of the human masseter using a strictly controlled method in which stimulus conditions, MU firing frequency, and motor task were matched. All MUs were inhibited by a non-noxious electrical stimulus delivered to the oral mucosa. Although there were significant differences between MUs in the duration of inhibition, this was not dependent on the location of the MUs within the muscle. It was concluded that MU inhibitory reflex behaviour in the masseter is not region specific.

Action Potentials↗