Modulation of mandibular loading and bite force in mammals during mastication

Abstract

SUMMARY 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(ϵ1) and minimum (ϵ2) 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.)

In vivostrains in the femur of river cooter turtles(Pseudemys concinna) during terrestrial locomotion: tests of force-platform models of loading mechanics

“…humans, 5000-22 000 s -1 (Burr et al, 1996); dog and horse, ~100 000 s -1 (Rubin and Lanyon, 1982)]. Moreover, as noted in studies of mammalian feeding (Ross et al, 2007), strain magnitude is strongly correlated with strain rate (Fig. 4), such that steps in which the femur experiences higher strains tend to be steps in which the limb is loaded more quickly.…”

“…Measurements of peak strain rate from the 'dorsal' gauge location were used to determine rates of strain for mechanical property testing of the limb bones. Strain magnitudes were also regressed on strain rates from corresponding steps to evaluate the relationship between load rate and magnitude for turtle femora (Ross et al, 2007).…”

“…Rubin and Lanyon, 1982;Biewener et al, 1983;Nunamaker et al, 1990;Davies et al, 1993;Blob and Biewener, 1999;Demes et al, 2001;Main and Biewener, 2004;Main and Biewener, 2007). Strain data are also particularly amenable to analyses of loading rates (Ross et al, 2007), providing an additional method for assessing differences in bone mechanics across species. Based on our forceplatform analyses of femoral stresses in cooters (Butcher and Blob, 2008) and in vivo femoral strains recorded from other reptiles (Blob and Biewener, 1999), we hypothesized that the femur of cooters would experience high magnitudes of shear strain, indicating that torsional loading is not exclusive to animals that drag a large tail (Reilly et al, 2005) and may be a fundamental mechanical consequence of sprawling limb posture.…”

Rhythmic chewing with oral jaws in teleost fishes: a comparison with amniotes

“…Indeed, highly stereotyped jaw movements may be Table3). The relationship across lepidosaurs is not significant (Ross et al, 2007b).…”

Mammalian Oral Rhythms and Motor Control

“…The authors believed this was most likely due to an increase in the excitability of jaw closer motoneurons produced by activation of muscle spindles within the jaw closer muscles. Similarly, Ross' group recently demonstrated that bite force was modulated during SC, primarily by varying the rate at which force was generated in the jaw closers of macaques (Ross et al, 2007a). In other words, as the resistance in food properties increased, not only did the number of recruited muscle fibers increase, but the rate at which muscle fibers were recruited increased as well, so that the increased load did not significantly impact the www.intechopen.com duration of jaw closure.…”