Meeting Abstract
S2.9 Tuesday, Jan. 4 Mastication and the Postorbital Ligament: Dynamic Strain in Soft Tissues HERRING, S.W.*; RAFFERTY, K.L.; LIU, Z.J.; LEMME, M.; Univ. of Washington, Seattle herring@uw.edu
Collagenous ligaments resist tension but are useless under other loading regimes. Whereas the periodontal and the jaw joint capsular ligaments are intrinsic parts of masticatory mechanics, this is less clear for other ligaments. The postorbital ligament (POL) is the thickened edge of a septum dividing the orbital contents from the temporal fossa. As a tensile element, the POL might support the zygomatic arch against the pull of the masseter muscle. An ossified postorbital bar has evolved repeatedly in mammals, and in higher primates ossification extends to form a complete bony partition. Although ossification enables the postorbital bar to function in compression and shear, the most popular explanation involves isolating the orbital contents from distortions produced by contractions of the temporalis muscle. We examined linear deformation of the unossified POL in miniature pigs, Sus scrofa (n=7), along with electromyography of the jaw muscles and an assessment of pressure and shape changes in the temporalis during mastication. The POL elongated slightly but consistently (average 1.0%, range 0.1-3.0%) in synchrony with the contraction of the jaw elevator muscles, returning to resting length during opening. Although the temporalis bulged outward and created substantial pressure against the braincase, it usually retracted away from the POL. In anesthetized animals, opening the jaw increased pressure beneath the temporalis, but had no consistent effect on the POL. Stimulation of individual muscles produced elongation of up to 1.9%, with the most consistent muscle being the ipsilateral masseter. These results confirm that the POL is indeed a tension member and that jaw muscle contraction can potentially distort the orbital contents, and show further that the masseter has at least as much potential for elongating the postorbital ligament as does the temporalis. Supported by NIDCR DE08513.
