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

Abstract

Understanding the mechanical features of cortical bone and their changes with growth and adaptation to function plays an important role in our ability to interpret the morphology and evolution of craniofacial skeletons. We assessed the elastic properties of cortical bone of juvenile and adult baboon mandibles using ultrasonic techniques. Results showed that, overall, cortical bone from baboon mandibles could be modeled as an orthotropic elastic solid. There were significant differences in the directions of maximum stiffness, thickness, density, and elastic stiffness among different functional areas, indicating regional adaptations. After maturity, the cortical bone becomes thicker, denser, and stiffer, but less anisotropic. There were differences in elastic properties of the corpus and ramus between male and female mandibles which are not observed in human mandibles. There were correlations between cortical thicknesses and densities, between bone elastic properties and microstructural configuration, and between the directions of maximum stiffness and bone anatomical axes in some areas. The relationships between bone extrinsic and intrinsic properties bring us insights into the integration of form and function in craniofacial skeletons and suggest that we need to consider both macroscopic form, microstructural variation, and the material properties of bone matrix when studying the functional properties and adaptive nature of the craniofacial skeleton in primates. The differences between baboon and human mandibles is at variance to the pattern of differences in crania, suggesting differences in bone adaption to varying skeletal geometries and loading regimes at both phylogenetic and ontogenetic levels.Keywords craniofacial skeleton; biomechanics; function; adaptation; Micro-CT; primate Elastic properties and their variations in individuals are important for understanding bone adaptations and quality at the tissue level (Dechow et al., 1992(Dechow et al., , 1993Dechow and Hylander, 2000; Schwartz-Dabney and Dechow, 2003;Wang and Dechow, 2006;Wang et al., 2006; Rapoff et al., 2008). They are especially indispensable for exploring the biomechanics and adaptation of primate skulls using Finite Element Analysis (FEA) (Strait et al., 2005(Strait et al., , 2009Wang and Dechow, 2006;Wang et al., 2006; Rayfield, 2007). We have * Please send page proofs and direct correspondence to: Dr Qian Wang, Division of Basic Medical Sciences, Mercer University School of Medicine, 1550 College Street, Macon, GA 31207. Phone:478-301,4043; Fax: 478-301,5489; wang_q2@mercer.edu NIH Public Access Author ManuscriptAm J Phys Anthropol. Author manuscript; available in PMC 2011 April 1. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript systematically collected elastic properties from the craniofacial skeletons of three species including modern humans (crania and mandibles), macaques (crania), and baboons (crania) (Peterson, 2002; Peterson and Dechow, 2003; Dechow, 2002a, 2003;Dechow, 2006, Wang et al, 2006)...

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