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Variation in the apparent stiffness of cancellous bone is generally ascribed to variation in cancellous structure and density, while the bone tissue stiffness is assumed to be constant. The purpose of the present study was to examine whether the bone tissue stiffness is dependent on the direction and density of the cancellous structure. Bone tissue stiffness was estimated by combining mechanical testing and micro-finite element (micro-FE) modeling on cylindrical bone specimens obtained from the human mandibular condyle. One set of specimens was tested in the vertical direction of the condyle (n = 39) and another set in the transverse direction (n = 30). The cancellous structure of the specimens was characterized by micro-CT. The apparent bone stiffnesses predicted by the FE model correlated strongly (r2 = 0.91) with the measured apparent bone stiffnesses. Apparent bone stiffness in the transverse direction was considerably smaller than that in the vertical direction. In contrast, the predicted bone tissue stiffness was significantly larger in the transverse direction (E = 13.70 GPa) than in the vertical direction (E = 11.87 GPa). In addition, bone tissue stiffness correlated negatively with the bone volume fraction and directional sensitivity of the bone tissue stiffness increased with a decrease of bone volume fraction. The results suggest that the transversely oriented trabeculae in the mandibular condyle are stiffer and more mineralized than the vertically oriented trabeculae and that bone loss is compensated by an increase in the degree of mineralization. [ABSTRACT FROM AUTHOR]

In the present study, we tested the hypothesis that the cancellous bone of the mandibular condyle is inhomogeneous and anisotropic. For this purpose, 11 mandibular condyles from embalmed human cadavers were scanned in a micro-CT system. Within each condyle, 9 volumes of interest were selected from different mediolateral and supero-inferior regions. Several bone parameters were calculated to describe the morphology. It appeared that the cancellous bone of the condyle could be approximated by parallel plates. These plates were almost vertically oriented at an angle of 17° relative to the sagittal plane, i.e., perpendicular to the condylar axis. In the superior regions of the condyle, the cancellous bone had the largest bone volume fraction (0.19), associated with the thickest trabeculae (0.1 1 mm), and the highest trabecular number (1.72 mm-1). The lowest bone volume fraction (0.15) was found more inferiorly. The degree of anisotropy increased from superior to inferior across the condyle. No mediolateral differences in bone morphology were found, but superiorly central regions contained more bone than peripheral regions. The plate-like trabeculae could indicate that the condyle is optimally adapted to sustain loads from all directions in a plane perpendicular to the condylar axis. The high bone mass and lower anisotropy in the superior regions could enable the condyle to sustain multiple load directions. Toward the collum, the trabeculae are more aligned. This could point to stresses acting predominantly in one direction. [ABSTRACT FROM AUTHOR]