Bone undergoes constant remodeling throughout life. The cellular and biochemical mechanisms of bone remodeling vary in a region-specific manner. There are a number of notable differences between the mandible and long bones, including developmental origin, osteogenic potential of mesenchymal stem cells, and the rate of bone turnover. Collagen, the most abundant matrix protein in bone, is responsible for determining the relative strength of particular bones. Posttranslational modifications of collagen, such as intermolecular crosslinking and lysine hydroxylation, are the most essential determinants of bone strength, although the amount of collagen is also important. In comparison to long bones, the mandible has greater collagen content, a lower amount of mature crosslinks, and a lower extent of lysine hydroxylation. The great abundance of immature crosslinks in mandibular collagen suggests that there is a lower rate of cross-link maturation. This means that mandibular collagen is relatively immature and thus more readily undergoes degradation and turnover. The greater rate of remodeling in mandibular collagen likely renders more flexibility to the bone and leaves it more suited to constant exercise. As reviewed here, it is important in clinical dentistry to understand the distinctive features of the bones of the jaw.

At present, little is known about the age-related changes in jaw bones. The aim of this study was to characterize the mandibles of 6 month-old senile osteoporotic mice, SAMP6, and compare with those of age-matched controls, SAMR1. In comparison to SAMR1, SAMP6 showed thinner cortical bone, lower bone volume, and poorly organized collagen matrix. The collagen fibril diameter in SAMP6 was significantly smaller than that of SAMR1. In SAMP6 both collagen content and cross-links were lower than those of SAMR1, but the ratio of the major mature cross-link (pyridinoline) to its precursor reducible cross-link (dehydrodihydroxylysinonorleucine/its ketoamine) was higher in comparison to SAMR1. In addition, the extent of lysine hydroxylation of collagen was higher in SAMP6 than that of SAMR1. These results indicate that not only the quantity of collagen but also its quality are altered in SAMP6 and may result in the age-associated osteoporotic defects of mandibles.

Minerals and collagen are major components of bone. At present, little is known about the material property of the jaw bone compared to other bones of the body. The purpose of this study was to characterize the material property of mandibular bone expressed by the amount of mineral, collagen, and hydroxylysine (Hyl) in comparison with humeral and femoral bones using human cadavers. Mineral and collagen contents were significantly higher in the mandible than in humerus and femur but Hyl was significantly lower in the mandible. Among the three indices, a weak but significantly positive correlation between collagen and mineral contents was observed. On the contrary, Hyl showed a weak but significantly negative correlation with mineral. The three indices were almost not affected by aging, gender, and dental status which were thought to influence bone quantity. These results suggest that human mandibular bone differs in material property from humeral and femoral bones, and may possess a higher mechanical property explained by the hypothesis that adequate and no excessive extent of lysine hydroxylation of collagen leads to optimal collagen fibrillogenesis and matrix mineralization. The assessment of bone property as shown in this study could disclose unknown characteristics which cannot be expressed by bone quantity.

Lysyl oxidase (LOX) is an amine oxidase that is critical for the stability of connective tissues. The secreted proLOX is enzymatically quiescent and is activated through proteolytic cleavage between residue Gly162 and Asp163 (residue numbers according to the mouse LOX) by bone morphogenetic protein (BMP)-1 gene products. Here we report a novel processing of proLOX identified in vitro and in vivo. Two forms of mature LOX were identified and characterized by their immunoreactivity to specific antibodies, amine oxidase activity and mass spectrometry. One form was identified as a well characterized BMP-1 processed LOX protein. Another was found to be a truncated form of LOX (tLOX) resulting from the cleavage at the carboxy terminus of Arg192. The tLOX still appeared to retain amine oxidase activity. The results from the proLOX gene deletion and mutation experiments indicated that the processing occurs independent of the cleavage of proLOX by BMP-1 gene products and likely requires the presence of LOX propeptide. These results indicate that proLOX could be processed by two different mechanisms producing two forms of active LOX.

Studies of chemical and electronic interaction at organic/inorganic interfaces are described. Electrochemical deposition of conducting polymers [poly(3-methylthiophene), polythiophene, poly(3-methylpyrrole), polypyrrole, poly(3methyithiophene-co-pyrrole)] on an n-Si wafer does not give rise to high-quality p-n heterojunctions, but it is found that their junction properties are greatly improved by their electrochemical reduction (cathodic treatment). For example, the cathodic treatment of an as-grown poly(3-methylthiophene)/n-Si junction cell with rectifying ratio, y, of 1.4 x 10' and diode factor, n, of 2.6 gives a high quality junction with y = 1.7 X io and n = 1.2. The treatment involves not only the development of polymer films but the improvement in junction interface, since the treatment can contribute to the improvement only when conducted in the presence of polymer films. In order to understand this modification at the interface, the effects of cathodic treatment conditions (treatment potential and time) and the presence of an interfacial oxide layer on the junction properties are investigated. As a result, it is revealed that the improvement is explained by a junction formation model described as the evolution of covalent bond formation at the interface. Further electrochemical studies reveal that such bondings are disrupted by hydrolysis and/or oxidation, and the bond disruption model is used to describe the degradation of the junctions in the air.