Abstract:
OBJECTIVES:This research theoretically models and empirically records symphyseal surface strain during in vitro human mandibular wishboning (lateral transverse bending) in order to test one aspect of the hypothesis that the chin is an adaptive response to masticatory stresses. From a perspective of optimality, three questions were tested: 1) Do human mandibles function as curved beams during wishboning? 2) Is the presence of a chin associated with lower than predicted curved beam effects? 3) Are there relatively low strain gradients on the lingual and labial symphyseal surfaces respectively? MATERIALS AND METHODS:Based on morphometric criteria, theoretical wishboning strains were calculated for five dentate adult human mandibles. The same mandibles were fitted with strain gauges and subjected to simulated wishboning loads. From the empirically-recorded strains, relative strains were calculated by dividing all strains by the absolute lowest strain in a given specimen. The theoretical and empirical results were compared in order to address the three related questions guiding this research. RESULTS:Human mandibles behave as curved beams during wishboning (question 1). Empirical strain measures showed greater disparity both between and within the labial and lingual symphyseal surfaces than the theoretical models predictions (questions 2 and 3). DISCUSSION:Human symphyseal form, with its distinctive chin, is unlikely to be adapted for countering wishboning loads. Chins are associated with larger than expected strain gradients within and between symphyseal surfaces, which runs counter to the optimality criterion typically invoked in assessing trait performance for signs of adaptation. The implications are twofold: 1) wishboning may not, in fact, be a regular feature of human mastication or 2) wishboning may not pose the same structural risks in human jaws as this load does in other anthropoid primates.
journal_name
Am J Phys Anthropoljournal_title
American journal of physical anthropologyauthors
Pampush JD,Daegling DJdoi
10.1002/ajpa.22863subject
Has Abstractpub_date
2016-02-01 00:00:00pages
256-66issue
2eissn
0002-9483issn
1096-8644journal_volume
159pub_type
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