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Results for “Masseter Muscle”

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At least 613 records · Page 34Linked to original sources
PubMed1993

Electromyographic turns analysis of sustained contraction in human masseter muscles at various isometric force levels.

The jaw-closing muscles differ from peripheral limb muscles in that the maximum attainable force does not decline following a sustained isometric contraction. Also, the averaged electromyographic (EMG)/force ratio in these muscles does not change with sustained contraction, whereas it increases in fatiguing limb muscles. The present study analysed EMG records from masseters in healthy male subjects. No statistically significant difference was seen between average rectified EMG signals at the beginning or the end of a sustained isometric contraction at 25-100% of maximum voluntary contraction (MVC). However, when the number of turns, or reversals of direction, was taken at various percentage MVC levels, a significant decrease was seen after 60s or at the end of the contraction. The turns/force ratio decreased monotonically with percentage MVC, but the ratio was not significantly different at the end of a contraction from that at the beginning. This result confirms an earlier suggestion that neuromuscular fatigue does not accompany sustained contractions of these muscles.

Adult↗
PubMed2001

Developmental expression of vascular endothelial growth factor in the masseter muscle of rats.

Developmental changes in vascular endothelial growth factor (VEGF) in rat masseter after birth were investigated. VEGF was extracted efficiently and reproducibly from muscle homogenate with low concentrations of non-ionic detergents, such as Triton X-100, Nonidet P-40, and Tween 20. The amount of VEGF measured by enzyme-linked immunosorbent assay (ELISA) increased markedly by approximately 9-fold, from day 8 to 35 after birth. The increase in VEGF was closely correlated with the development of the capillary network, as shown by the capillary to muscle fibre ratio (C/F ratio). Immunoblotting revealed that the predominant molecular species of VEGF concentrated with heparin-sepharose beads was VEGF(188). These results suggest that VEGF plays an important part in the development and maintenance of the capillary network in the rat masseter.

Animals↗
PubMed2006

[Relationship between jaws and the masseter muscle by superimposing MR images on the cephalogram].

The purpose of this study was to observe the morphological relationship between maxillofacial skeleton and masseter by superimposing the masseter image constructed by MR image scanning on the cephalogram. Sixteen subjects with different mandibular plane angle were examined in this study. Cephalogram and MR images of each subject were taken, and the images were input to a computer by using a digitizer. The areas of masseter were selected in each MR scan image which were projected to the mid-sagittal layer of the MR scan images. The synthesized image of cephalogram and masseter was obtained by completely superimposing sagittal images of the masseter with the mid-sagittal-plane MR image on the cephalogram. The inclination of masseter was determined by the center of gravity on the cross-section of masseter. These synthesized images of cephalogram and masseter showed various shapes of masseter according to different mandibular plane angle. The inclination of masseter had a close correlation with some skeletal parameters (mandibular plane angle, ANB, Y-axis, facial angle, saddle angle) of cephalometric analysis. The volume of the masseter also had a close correlation with skeletal parameters (mandibular plane angle, gonial angle, Y-axis). These results revealed that morphometric analysis using synthesized images of cephalogram and masseter is useful, and that the inclination and the volume of masseter may have an influence on the shape of the mandibular bone and its vertical and anteroposterior development.

Adult↗
PubMed1991

[Reflex response in the masseter muscle after tapping the chin in healthy persons--an electromyographic study].

In a group of healthy subjects the author evoked reflex responses in both masseters by percussion of the chin with a reflex hammer. The reflexes were evoked during relaxation, slight or intense contraction of the masseters with the mouth open or closed. By percussion of the chin from above extension reflexes were evoked and by percussion of the chin from below contracting reflexes. The response was recorded by means of an electromyographic apparatus. The short-term stretch responses were evoked from the relaxed and slightly contracted masseters with the mouth open or closed. During intense contraction of the masseters the short-latency reflex stretch response was not evoked. In that case at first a short-latency inhibition of the basal activity of the masseter was observed followed by a medium and late-latency excitation response. With the masseters relaxed a long-latency stretch response was observed only with the mouth open. Percussion of the chin from beneath with slight contraction of the masseter caused initial inhibition of its basal activity followed then by a short-latency excitation response. Based on the assembled results the author analyzed the mechanism of the reflex control of the masseters.

Chin↗