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Outer shape changes of human masseter with contraction by ultrasound morphometry.
Kei Kubo1, Tetsuo Kawata, Toru Ogawa
1Division of Advanced Prosthetic Dentistry, Tohoku University, Graduate School of Dentistry, 4-1 Seiryo-machi, Aoba-ku, Sendai 9808575, Japan. kei-thk@umin.ac.jp
Archives of Oral Biology
|August 16, 2005
Summary
Masseter muscle thickness changes unevenly during clenching due to its complex structure. This study used ultrasound to map these heterogeneous shape alterations in the masseter muscle.
Area of Science:
- Anatomy
- Biomechanics
- Medical Imaging
Background:
- The masseter muscle's multipennate structure suggests non-uniform contraction.
- Heterogeneous muscle contraction can lead to inequable changes in outer shape.
Purpose of the Study:
- To investigate the outer shape changes of the entire masseter muscle during clenching.
- To analyze masseter muscle deformation using multipoint measurements from serial ultrasound images.
Main Methods:
- Serial coronal ultrasound images of the masseter were acquired from five healthy men.
- A 3D mechanical stage and face-bow were used for precise transducer-cranium positioning.
- Muscle thickness was measured at 1mm intervals from origin to insertion during relaxation and maximal clenching.
Main Results:
- Masseter muscle thickness varied significantly across measurement points during clenching.
- Most sites increased in thickness, but some, particularly near origin/insertion, decreased.
- Positive correlations were found between relaxed thickness (R) and contracted thickness (C), and between C and thickness change (Delta).
Conclusions:
- Clenching causes disparate thickness changes within the masseter muscle.
- These variations likely stem from the muscle's multipennate architecture and functional heterogeneity.
- The complex contraction properties contribute to the observed uneven shape alterations.