Quantification of porosity and degree of mineralization of bone facilitates a better understanding of the possible effects of adaptive bone remodelling and the possible consequences for its mechanical properties. The present study set out first to give a three-dimensional description of the cortical canalicular network in the human mandibular condyle, in order to obtain more information about the principal directions of stresses and strains during loading. Our second aim was to determine whether the amount of remodelling was larger in the trabecular bone than in cortical bone of the condyle and to establish whether the variation in the amount of remodelling was related to the surface area of the cortical canals and trabeculae. We hypothesized that there were differences in porosity and orientation of cortical canals between various cortical regions. In addition, as greater cortical and trabecular porosities are likely to coincide with a greater surface area of cortical canals and trabeculae available for osteoblastic and osteoclastic activity, we hypothesized that this surface area would be inversely proportional to the degree of mineralization of cortical and trabecular bone, respectively. Micro-computed tomography was used to quantify porosity and mineralization in cortical and trabecular bone of ten human mandibular condyles.The cortical canals in the subchondral cortex of the condyle were orientated in the mediolateral direction, and in the anterior and posterior cortex in the superoinferior direction. Cortical porosity (average 3.5%) did not differ significantly between the cortical regions. It correlated significantly with the diameter and number of cortical canals, but not with cortical degree of mineralization. In trabecular bone (average porosity 79.3%) there was a significant negative correlation between surface area of the trabeculae and degree of mineralization; such a correlation was not found between the surface area of the cortical canals and the degree of mineralization of cortical bone. No relationship between trabecular and cortical porosity, nor between trabecular degree of mineralization and cortical degree of mineralization was found, suggesting that adaptive remodelling is independent and different between trabecular and cortical bone. We conclude (1) that the principal directions of stresses and strains are presumably directed mediolaterally in the subchondral cortex and superoinferiorly in the anterior and posterior cortex, (2) that the amount of remodelling is larger in the trabecular than in the cortical bone of the mandibular condyle; in trabecular bone variation in the amount of remodelling is related to the available surface area of the trabeculae.

Regenerative therapies offer attractive alternatives for the treatment of osteochondral defects. Adipose-derived stromal vascular fraction (SVF) cells allow the development of one-step surgical procedures by their abundant availability and high frequency. In this pilot study we evaluated the in vivo safety, feasibility, and efficacy of this concept using scaffolds seeded with freshly isolated (SVF) or cultured adipose stem cells (ASCs), and compared these to their acellular counterparts. Osteochondral defects were created in medial condyles and trochlear grooves in knees of eight goats. Defects were filled with acellular collagen I/III scaffolds or scaffolds seeded with SVF cells or cultured ASCs. Osteochondral regeneration was evaluated after 1 and 4 months by macroscopy, immunohistochemistry, biomechanical analysis, microCT analysis, and biochemistry. After 1 month, no adverse effects were noted. Microscopic, but not macroscopic evaluation showed considerable yet not significant differences, with cell-loaded constructs showing more extensive regeneration. After 4 months, acellular constructs displayed increased regeneration, however, to a lesser degree than cell-treated constructs. The latter exhibited more extensive collagen type II, hyaline-like cartilage, and higher elastic moduli, and their glycosaminoglycan content in the cartilaginous layer better approached native tissue values. Moreover, their defect regions contained higher levels of regenerated, mature subchondral bone with more intense collagen type I staining. SVF cells tended to perform best on all parameters. In summary, this pilot study demonstrated the preclinical safety and feasibility of a one-step surgical procedure for osteochondral defect regeneration. Similar regeneration was found between freshly isolated SVF cells and cultured ASCs. Larger studies with longer follow-up are required to substantiate these findings.

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The degree of mineralization of bone (DMB) in the mandibular condyle reflects the age and remodeling rate of the bone tissue. Quantification of DMB facilitates a better understanding of possible effects of adaptive remodeling on mineralization of the condyle and its possible consequences for its mechanical quality. We hypothesized differences in the degree and distribution of mineralization between trabecular and cortical bone and between various cortical regions. Microcomputed tomography was used to measure mineralization in 10 human mandibular condyles. Mean DMB was higher in cortical (1,045 mg hydroxyapatite/cm(3)) than in trabecular bone (857 mg/cm(3)) and differed significantly between cortical regions (anterior 987 mg/cm(3), posterior 1,028 mg/cm(3), subchondral 1,120 mg/cm(3)). The variation of DMB distribution was significantly larger in the anterior cortex than in the posterior and subchondral cortex, indicating a larger amount of heterogeneity of mineralization anteriorly. Within the cortical bone, DMB increased with the distance from the cortical canals to the periphery. Similarly, the DMB of trabecular bone increased with the distance from the surface of the trabeculae to their cores. It was concluded that the rate of remodeling differs between condylar trabecular and cortical bone and between cortical regions and that DMB is not randomly distributed across the bone. The difference in DMB between condylar cortical and trabecular bone suggests a large difference in Young's modulus.

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Our findings provide more insight into bone-site-specific effects of bisphosphonates and into the aetiology of osteonecrosis of the jaw. We demonstrated that bisphosphonates can stimulate osteoclast activity at the molar roots.

The EPIC-µCT technique is effective for the ex vivo assessment of 3D cartilage morphology in the mouse as well as human TMJ and allows bone-cartilage interaction research in TMJ-OA.