Ontogeny of material stiffness heterogeneity in the macaque mandibular corpus

Abstract

Evidence is accumulating that bone material stiffness increases during ontogeny, and the role of elastic modulus in conditioning attributes of strength and toughness is therefore a focus of ongoing investigation. Developmental changes in structural properties of the primate mandible have been documented, but comparatively little is known about changes in material heterogeneity and their impact on biomechanical behavior. We examine a cross-sectional sample of Macaca fascicularis (N = 14) to investigate a series of hypotheses that collectively evaluate whether the patterning of material stiffness (elastic modulus) heterogeneity in the mandible differs among juvenile, subadult and adult individuals. Because differences in age-related activity patterns are known to influence bone stiffness and strength, these data are potentially useful for understanding the relationship between feeding behavior on the one hand and material and structural properties of the mandible on the other. Elastic modulus is shown to be spatially dependent regardless of age, with this dependence being explicable primarily by differences in alveolar versus basal cortical bone. Elastic modulus does not differ consistently between buccal and lingual cortical plates, despite likely differences in the biomechanical milieu of these regions. Since we found only weak support for the hypothesis that the spatial patterning of heterogeneity becomes more predictable with age, accumulated load history may not account for regional differences in bone material properties in mature individuals with respect to the mandibular corpus.

Spatial patterning of bone stiffness in the anterior mandibular corpus of Macaca fascicularis: Implications for models of bone adaptation

“…basal symphysis serves to reduce the nominal tensile stresses that arise from this loading regime. Here again, however, it may not be best explained as a material "adaptation," as stiff basal bone is characteristic of the postcanine mandible as well (Daegling et al, 2011(Daegling et al, , 2014, where coronal bending is presumably absent. Dorsoventral shear could be expected to produce a more or less uniform distribution of strain in the symphysis, but the spatial variation in elastic modulus that characterizes the sample probably ensures that this is not the case in vivo.…”

“…One finding of this investigation at odds with other data is the inconsistent finding of more compliant alveolar bone in the macaque symphysis. Other study suggests that alveolar bone is routinely more compliant than bone along the basal aspect of the mandible (Daegling et al, 2011(Daegling et al, , 2014 although these data focused on mandibular corpus bone generally rather than bone specific to the symphyseal region. The hypothesis has been advanced that compliant alveolar bone serves as a local stress shield in which stresses from occlusal loads is conducted or attracted to denser, stiffer, and stronger basal bone (Daegling et al, 2011).…”

The ontogeny of the chin: an analysis of allometric and biomechanical scaling

“…Hylander, 1984Hylander, , 1985. Variation in load magnitude and frequency associated with variability in dietary properties, as well as nondietary paramasticatory behaviors, has been used to explain variation in mandibular form across a wide range of extant and fossil primate taxa (Hylander, 1984(Hylander, , 1985Ravosa, 1990Ravosa, , 1996aDaegling & Grine, 1991;Ravosa & Simons, 1994;Vinyard & Ravosa, 1998;Daegling, 2001;Daegling et al , 2014. In particular, there has been considerable emphasis placed on the interaction between masticatory loads and mandibular symphyseal morphology.…”

Diet, feeding behavior, and jaw architecture of Taï monkeys: Congruence and chaos in the realm of functional morphology

“…One pattern originally identified in colobines, namely low material stiffness in the alveolar process and higher stiffness in the basal corpus, extends to the Taï cercopithecines as well . This also characterizes at least one species of macaque . Relatively compliant alveolar bone is thus a feature of all monkeys sampled, and this feature transcends feeding and dietary differences.…”

“…35,36 This also characterizes at least one species of macaque. 37 Relatively compliant alveolar bone is thus a feature of all monkeys sampled, and this feature transcends feeding and dietary differences.…”