Dynamic finite element modelling of the macaque mandible during a complete mastication gape cycle

Abstract

Three-dimensional finite element models (FEMs) are powerful tools for studying the mechanical behaviour of the feeding system. Using validated, static FEMs we have previously shown that in rhesus macaques the largest food-related differences in strain magnitudes during unilateral postcanine chewing extend from the lingual symphysis to the endocondylar ridge of the balancing-side ramus. However, static FEMs only model a single time point during the gape cycle and probably do not fully capture the mechanical behaviour of the jaw during mastication. Bone strain patterns and moments applied to the mandible are known to vary during the gape cycle owing to variation in the activation peaks of the jaw-elevator muscles, suggesting that dynamic models are superior to static ones in studying feeding biomechanics. To test this hypothesis, we built dynamic FEMs of a complete gape cycle using muscle force data from in vivo experiments to elucidate the impact of relative timing of muscle force on mandible biomechanics. Results show that loading and strain regimes vary across the chewing cycle in subtly different ways for different foods, something which was not apparent in static FEMs. These results indicate that dynamic three-dimensional FEMs are more informative than static three-dimensional FEMs in capturing the mechanical behaviour of the jaw during feeding by reflecting the asymmetry in jaw-adductor muscle activations during a gape cycle. This article is part of the theme issue ‘Food processing and nutritional assimilation in animals’.

Rhythmic chew cycles with distinct fast and slow phases are ancestral to gnathostomes

“…Fortunately, X-ray-based data on gape kinematics are rapidly becoming available from a swath of lepidosaurs and mammals (e.g. [69][70][71]), which will facilitate future velocity-based analyses of chew cycle partitioning into phases.…”

Introduction: food processing and nutritional assimilation in animals

“…Püffel et al [40] define mandibular performance in feeding ants using bite force production, and Richter & Economo [38] discuss performance though food uptake rates and feeding duration. Similarly, Bels et al [55] [21] all assess feeding performance through jaw and tongue kinematics, as well as muscle performance (length-change), whereas Panagiotopoulou et al [56] use bone strain. Strain patterns and changes in muscle architecture are proxies for force production, energetic costs and feeding duration; although we note that many of the relationships between measures of performance remain tenuous (with noted exceptions, e.g.…”

“…However, studies relating food material properties to oral processing in vertebrates are limited outside of primates (but see, [44,77,81]). In this special issue, Stilson et al [21], Laird et al [32], Wall et al [61] and Panagiotopoulou et al [56] all explore effects of varying food substrates during oral processing. Despite the importance of understanding the physics of a food substrate, this element of oral processing has thus far had a relatively limited effect on linking diet and morphology within primates [14].…”

“…[ 21 ] all assess feeding performance through jaw and tongue kinematics, as well as muscle performance (length-change), whereas Panagiotopoulou et al . [ 56 ] use bone strain. Strain patterns and changes in muscle architecture are proxies for force production, energetic costs and feeding duration; although we note that many of the relationships between measures of performance remain tenuous (with noted exceptions, e.g.…”

“…[ 61 ] and Panagiotopoulou et al . [ 56 ] all explore effects of varying food substrates during oral processing. Despite the importance of understanding the physics of a food substrate, this element of oral processing has thus far had a relatively limited effect on linking diet and morphology within primates [ 14 ].…”