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Length changes in the human masseter muscle after jaw movement
T K Goto1, G E Langenbach, A G Hannam
1Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Kyushu University, Higashi-ku, Fukuoka-City, Japan.
The Anatomical Record
|March 10, 2001
Summary
The human masseter muscle stretches unevenly during jaw movements. Different parts of the masseter, particularly the deep masseter, show significant length changes, indicating task-specific tension variations.
Area of Science:
- Biomechanics
- Human Anatomy
- Musculoskeletal System
Background:
- The human masseter muscle is crucial for jaw motion.
- Variations in muscle stretch can affect fiber function along length-tension curves.
Purpose of the Study:
- To quantify length changes in different parts of the masseter muscle during voluntary jaw movements in living subjects.
Main Methods:
- Magnetic resonance (MR) imaging and optical jaw-tracking were employed.
- Muscle insertion positions were measured in six degrees of freedom (DOF).
- Calculations included muscle part lengths, intramuscular tendon lengths, and estimated fiber-length changes.
Main Results:
- Maximum jaw opening caused the largest length increases (34-83%) in the medial deep masseter.
- The superficial masseter showed smaller changes (2-19%) during maximum opening.
- Ipsilateral jaw movements resulted in minimal length changes compared to protrusion and contralateral movements.
Conclusions:
- The masseter muscle exhibits non-uniform stretching during major jaw movements.
- Different regions of the masseter experience task-related changes in active and passive tensions.
- Tendon stretch has a limited impact on estimated fiber length changes.