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Mastication and the postorbital ligament: dynamic strain in soft tissues
Susan W Herring1, Katherine L Rafferty, Zi Jun Liu
1Department of Orthodontics, School of Dentistry, University of Washington, Seattle, USA. herring@uw.edu
Integrative and Comparative Biology
|May 20, 2011
Summary
Jaw muscle contractions stretch the postorbital ligament during chewing in minipigs. This suggests the ligament acts as a tension member, resisting masseter muscle pull on the zygomatic arch.
Area of Science:
- Biomechanics
- Mammalian anatomy
- Physiology
Background:
- The postorbital ligament, a fascial complex, may support the zygomatic arch against jaw muscle forces.
- Ossified postorbital bars in mammals resist skull deformation, but their precise function remains debated.
- Previous studies have not demonstrated deformation of the unossified ligament by jaw muscle contraction.
Purpose of the Study:
- To investigate the interaction between muscle activity and ligamentary stretch during mastication.
- To determine if jaw muscle contraction deforms the postorbital ligament.
- To assess the functional role of the postorbital ligament in resisting masticatory forces.
Main Methods:
- Electromyography of jaw muscles in minipigs (Sus scrofa).
- Measurement of linear deformation of the postorbital ligament.
- Assessment of pressure and shape changes in the temporalis muscle.
Main Results:
- The postorbital ligament elongated during chewing, synchronized with elevator muscle contraction (average 0.9%, max 2.8%).
- Temporalis muscle bulging created pressure, but superficial fibers retracted away from the ligament.
- Isolated stimulation of temporalis or masseter muscles caused ligament elongation (average 0.4-0.7%).
Conclusions:
- Masticatory muscle contraction can potentially distort orbital contents.
- The postorbital ligament functions as a tension member, resisting the masseter muscle's pull on the zygomatic arch.
