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First published online March 2, 2007
Journal of Experimental Biology 210, 1046-1063 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02733

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Modulation of mandibular loading and bite force in mammals during mastication

Callum F. Ross^1,*, Ruchi Dharia², Susan W. Herring³, William L. Hylander⁴, Zi-Jun Liu³, Katherine L. Rafferty³, Matthew J. Ravosa⁵ and Susan H. Williams⁶

¹ Organismal Biology and Anatomy, University of Chicago, 1027 E. 57th Street, Chicago, IL 60637, USA
² Stony Brook School of Medicine, Health Sciences Center Level 4, Stony Brook, NY 11794-8434, USA
³ Department of Orthodontics, School of Dentistry, University of Washington, Seattle, WA 98195-357446, USA
⁴ Department of Biological Anthropology and Anatomy, Duke University Lemur Center, Durham, NC 27710, USA
⁵ Department of Pathology and Anatomical Sciences, University of Missouri School of Medicine, One Hospital Drive – Medical Sciences Building, Columbia, MO 65212, USA
⁶ Department of Biomedical Sciences, Ohio University College of Osteopathic Medicine, 228 Irvine Hall, Athens, OH 45701, USA

^* Author for correspondence (e-mail: rossc{at}uchicago.edu)

Accepted 25 January 2007

Modulation of force during mammalian mastication provides insight into force modulation in rhythmic, cyclic behaviors. This study uses in vivo bone strain data from the mandibular corpus to test two hypotheses regarding bite force modulation during rhythmic mastication in mammals: (1) that bite force is modulated by varying the duration of force production, or (2) that bite force is modulated by varying the rate at which force is produced. The data sample consists of rosette strain data from 40 experiments on 11 species of mammals, including six primate genera and four nonprimate species: goats, pigs, horses and alpacas. Bivariate correlation and multiple regression methods are used to assess relationships between maximum (₁) and minimum (₂) principal strain magnitudes and the following variables: loading time and mean loading rate from 5% of peak to peak strain, unloading time and mean unloading rate from peak to 5% of peak strain, chew cycle duration, and chew duty factor. Bivariate correlations reveal that in the majority of experiments strain magnitudes are significantly (P<0.001) correlated with strain loading and unloading rates and not with strain loading and unloading times. In those cases when strain magnitudes are also correlated with loading times, strain magnitudes are more highly correlated with loading rate than loading time. Multiple regression analyses reveal that variation in strain magnitude is best explained by variation in loading rate. Loading time and related temporal variables (such as overall chew cycle time and chew duty factor) do not explain significant amounts of additional variance. Few and only weak correlations were found between strain magnitude and chew cycle time and chew duty factor. These data suggest that bite force modulation during rhythmic mastication in mammals is mainly achieved by modulating the rate at which force is generated within a chew cycle, and less so by varying temporal parameters. Rate modulation rather than time modulation may allow rhythmic mastication to proceed at a relatively constant frequency, simplifying motor control computation.)

Key words: bone strain, muscle recruitment, size principle, chewing

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