Changes in Mandibular Cortical Bone Density and Elastic Properties during Growth
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© Cambridge University Press 2017. Introduction Cortical bone material properties including density and elastic properties (elastic modulus, shear modulus, and Poisson’s ratio) are essential for understanding the complex biomechanical responses of individual bones to muscle forces and extrinsic loadings (Dechow and Hylander, 2000; Strait et al., 2005). In particular, variations in cortical bone anisotropies are significant in determining the relationship between stress and strain in bone. In primate and human evolution, research on the craniofacial skeleton, including the mandible, suggests that variations in such properties may represent evolutionary adaptations to unique craniofacial functions or patterns of development (Wang et al., 2006). While there is a growing body of literature on intraspecific and interspecific adult variation in cortical bone material properties in primate craniofacial skeletons (Ashman et al., 1984; Dechow et al., 1992, 1993, 2008, 2010; Peterson and Dechow, 2002, 2003; Schwartz-Dabney and Dechow, 2002a, b, 2003; Lettry et al., 2003; Nomura et al., 2003; Peterson et al., 2006; Wang and Dechow, 2006; Rapoff et al., 2008; Q. Wang et al., 2010; Chung and Dechow, 2011; Daegling et al., 2011a, b, 2014; Davis et al., 2012; J. Wang et al., 2014), little is known about changes in these properties during growth (Ashman et al., 1984; Hara et al., 1998; Wang et al., 2010; Davis et al., 2012; Daegling et al., 2014). While it is understood that bone increases in mineralization during growth, there is little understanding of whether the regional variations in material properties seen in adults can also be found in juveniles and neonates, or whether these variations develop during growth in response to intrinsic and extrinsic biomechanical factors. Because of the overall unavailability of appropriate cadaver material, regionally comparative studies in primates have been limited to a single study in baboons (Wang et al., 2010) that contrasted juveniles and adults to explore questions of age changes in bone material properties. This chapter will examine these questions through the use of two unique data sets: (1) material properties of a sample of five neonatal human mandibles are contrasted with data from a sample of 17 adult humans; and (2) material properties of the mandibles of domestic pigs are contrasted across different mandibular regions at different ages.
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Building Bones: Bone Formation and Development in Anthropology