Material property variation of mandibular symphyseal bone in colobine monkeys

Abstract

The anterior mandibular corpus of anthropoid primates is routinely subjected to masticatory loads that result in relatively high local levels of stress and strain. While structural morphological responses to these loads have been extensively explored, relatively little is known about material property variation in mandibular bone of nonhuman primates. Consequently, the role of regional and local variation in bone stiffness in conditioning stress and strain gradients is poorly understood. We sampled elastic modulus variation in the bone of the anterior mandibular corpus in two species (N = 3 each) of sympatric colobine monkeys, Procolobus badius and Colobus polykomos. These monkeys were chosen for comparison owing to their distinctive dietary regimens, as P. badius rarely includes hard objects in its diet while C. polykomos habitually processes obdurate items during feeding. Elastic modulus is determined through bone hardness data obtained via microindentation, which enables the description of stiffness variation on sub-millimeter scales. Labial bone stiffness exceeds that of lingual bone in the sample overall. Female mandibular bone is generally stiffer than that found in males, and overall Procolobus mandibular bone is stiffer than that in Colobus. These results, interpreted collectively, suggest that the material response to elevated masticatory stress is increased compliance of the affected bone.

Application of Optimization Methodology and Specimen-Specific Finite Element Models for Investigating Material Properties of Rat Skull

“…Studies on an FE human mandible model demonstrated that the FE-predicted peak volumetric strain decreased when considering anisotropic elasticity. 11,15 These anisotropic characteristics were also confirmed through microindentation experiments by Daegling et al 6 In the only published study to investigate rat skull material properties experimentally, Gefen et al 8 analyzed the tissue as an isotropic elastic material. Therefore, for the current study, isotropic elastic-plastic behavior was assumed based on human data published by McElhaney et al 21 and Wood, 35 as well as the rat data from the Gefen et al 8 study.…”

Regional, ontogenetic, and sex‐related variations in elastic properties of cortical bone in baboon mandibles

“…This area resists wishboning during mastication and is subject to a variable range of loading regimes depending on oral function and bite point (Hylander, 1979a,b,c, 1988; Daegling and McGraw, 2009; Daegling et al, 2009). Recent studies on symphyseal strength demonstrate that baboon mandibles need up to 1.4 kN to reach failure during the wishboning loading experiments (Vinyard et al, 2006).…”

“…Recent studies on symphyseal strength demonstrate that baboon mandibles need up to 1.4 kN to reach failure during the wishboning loading experiments (Vinyard et al, 2006). Thick cortex might allow resistance to deformation and increased strength when possible loads are more variable in orientation, thus the lesser stiffness of the symphysis may reflect a decreased material density but not necessarily decreased structural strength (Dechow and Hylander, 2000; Daegling and McGraw, 2009; Daegling et al, 2009). This raises an excellent question for further testing with finite element analysis that would need to incorporate the cortical material properties described here, and information on the structure and density of the more porous internal structure of the symphysis, which remains to be investigated.,…”

Feeding and oral processing behaviors of two colobine monkeys in Tai Forest, Ivory Coast

“…Further, we lack information on the material properties of any colobine food. The importance of these omissions was underscored when micro-indentation experiments revealed significant variation in the elastic modulus of mandibular bone in the two Tai colobines (Daegling et al, 2009). These data indicated that symphyseal bone in P. badius was stiffer than that of C. polykomos, which led to the hypothesis that the demands of processing P. macrophylla fruits required that C. polykomos generate large masticatory forces and that the more compliant mandibular bone in black and white colobus was an adaptation for making bone tougher.…”