The relationship of in vivo bone strain to mandibular corpus morphology in Macaca fascicularis

Inferred patterns of mandibular bone stress derived from in vivo strain data are related to size and shape variation in the mandibular corpus of Macaca fascicularis . Size and shape are described in mechanical terms from the cross-sectional contours of compact bone at seven locations along the mandibular corpus. Area moments of inertia and section moduli are related to bending moment arms, cortical area is related to variation in total subperiosteal area, and an estimate of torsional strength is calculated. The distribution of masticatory stress in the macaque corpus is hypothesized to be highly inequitable; the symphysis and the most posterior region of the corpus (i.e., at the M2 and M3) are probably subjected to the highest normal stresses in lateral and parasagittal bending, respectively. The distribution of torsional shear stress in the mandible is difficult to model theoretically, although it is likely that these stresses also vary in magnitude in different regions of the corpus. These data indicate that the inference of masticatory stress patterns from purely morphological criteria in the absence of experimental corroboration is problematic. It is unlikely that regional variation in corpus mechanical properties directly reflects local differences in the relative magnitudes of different masticatory stress regimes.