The functional significance of primate mandibular form

Bibliographic Data

ID23322152
AuthorsWilliam L Hylander (Duke University, corresponding author)
Year1979
Volume160
Issue2
Pages223-239
Publication date1979-05-01
Peer ReviewedYes
Open AccessYes
TypeARTICLE
VenueJournal of Morphology (JOURNAL)
Journal identifiersISSN: 0362-2525 • E-ISSN: 1097-4687
PublisherWiley (PUBLISHER • GB)
DOI10.1002/jmor.1051600208
PMID458862
OpenAlexW2060918284
LanguageEN
Citations received185
References cited26

A stress analysis of the primate mandible suggests that vertically deep jaws in the molar region are usually an adaptation to counter increased sagittal bending stress about the balancing‐side mandibular corpus during unilateral mastication. This increased bending stress about the balancing side is caused by an increase in the amount of balancing‐side muscle force. Furthermore, this increased muscle force will also cause an increase in dorsoventral shear stress along the mandibular symphysis. Since increased symphyseal stress can be countered by symphyseal fusion and as increased bending stress can be countered by a deeper jaw, deep jaws and symphyseal fusion are often part of the same functional pattern. In some primates (e.g., Cercocebus albigena ), deep jaws are an adaptation to counter bending in the sagittal plane during powerful incisor biting, rather than during unilateral mastication. The stress analysis of the primate mandible also suggests that jaws which are transversely thick in the molar region are an adaptation to counter increased torsion about the long axis of the working‐side mandibular corpus during unilateral mastication. Increased torsion of the mandibular corpus can be caused by an increase in masticatory muscle force, an increase in the transverse component of the postcanine bite force and/or an increase in premolar use during mastication. Patterns of masticatory muscle force were estimated for galagos and macaques, demonstrating that the ratio of working‐side muscle force to balancing‐side muscle force is approximately 1.5:1 in macaques and 3.5:1 in galagos during unilateral isometric molar biting. These data support the hypothesis that mandibular symphyseal fusion is an adaptative response to maximize unilateral molar bite force by utilizing a greater percentage of balancing‐side muscle force.

Biology · Bite force quotient · Biting · Isometric exercise · Mandible (arthropod mouthpart) · Mandibular symphysis · Mastication · Masticatory force · Molar · Periodontal fiber · Premolar · Primate · Symphysis · Torsion (gastropod) · Zoology · Amphibian and Reptile Biology · Anatomy · Evolution and Paleontology Studies · Medicine · Orthodontics · Primate Behavior and Ecology

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