Elastic modulus variation in mandibular bone: A microindentation study of Macaca fascicularis

Abstract

We characterized the heterogeneous anisotropic elastic properties of mandibular bone in an adult female specimen of Macaca fascicularis using the technique of microindentation. This approach used an indenter of known mass and geometry to sample bone hardness at a spatial resolution in the order of 100 mum. Hardness values were converted to elastic modulus using empirically derived regression. We determined properties in alveolar, midcorpus, and basal regions of coronal and transverse sections taken from multiple locations along the corpus and ramus. Within sections, we determined properties from endosteal, midcortical, and periosteal regions. We found regional variations in bone structure, including bands of orthotropic circumferential lamellar bone at the endosteal and periosteal corpus base, angular region, and ramus. Transversely isotropic osteonal bone characterizes the midcortices of alveolar and basal regions, with many resorption spaces in alveolar regions restricting sampling opportunities. Regional variations in elasticity include relatively compliant bone in the anterior corpus and ramus. Basal cortical bone is stiffer longitudinally than transversely or superoinferiorly, while the evidence for directional dependence in alveolar bone is equivocal. Alveolar bone appears to be relatively compliant with respect to bone found in midcorpus or basal regions. Considerable variation exists in structure and material properties on a highly localized scale, more so than is discernible through conventional approaches for determining material property variation.

Masticatory stress and the mechanics of “wishboning” in colobine jaws

“…Thus, the distribution of material variation serves to exacerbate, rather than mitigate, curved beam effects in terms of strain. This does not appear to be the case in the single macaque that has been examined to date (Rapoff et al, 2008b).…”

Material property variation of mandibular symphyseal bone in colobine monkeys

“…Dechow and Hylander (2000) sampled cortical bone from the postcanine corpus of Macaca fascicularis using ultrasound, and determined that, in contrast to our findings at the symphysis, lingual bone tends to be stiffer than buccal (i.e., labial) bone. Recent microindentation of symphyseal bone in M. fascicularis along a superior transverse section indicates average stiffness on the order of 14-17 GPa (Rapoff et al, 2008), while those sections from the colobine sample exhibit larger values, averaging nearly 19 GPa. In the macaque symphysis, the lingual bone in the anterior corpus tends to be stiffer than the labial bone (Rapoff et al, 2008), an opposite relationship to that observed in the colobine sample.…”

“…With respect to bone, however, experimental data establish that hardness does have a predictable relationship to stiffness: the regression relating the hardness measure used in this study (see following text) to elastic modulus yields a coefficient of determination (r 2 ) of 0.93 (Rapoff et al, 2008). Hardness variation on a microscale can thus be used to evaluate stiffness variation.…”

“…We used a Vickers indenter in the present study, a pyramidal structure that produces symmetrical indentations. Use of this indenter assumes that the material is transversely isotropic; previous investigation of symphyseal bone in Macaca suggests that this is a reasonable assumption (Rapoff et al, 2008).…”

Ontogeny of material stiffness heterogeneity in the macaque mandibular corpus

“…Elastic modulus was determined through microindentation hardness testing (Rapoff et al, 2008) using protocols established by Johnson and Rapoff (2007). Coronal sections of 1 mm thickness were taken from the postcanine corpus below the M 1 using a diamond wafering blade on a low speed saw ((Buehler, Lake Bluff, IL).…”