Takashi Matsuura

Distinct Characteristics of Mandibular Bone Collagen Relative to Long Bone Collagen: Relevance to Clinical Dentistry

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.

Characterization of mandibular bones in senile osteoporotic mice.

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.

Biochemical Characterization of Collagen in Alveolar Mucosa and Attached Gingiva of Pig

Alveolar mucosa and attached gingiva are two continuous but functionally distinct connective tissues covering alveolar bone of the jaw. In this study, the major matrix component of these tissues, collagen, was biochemically characterized and compared. The tissues were obtained from mature pigs and analyzed for collagen content, amino acid composition, collagen types, collagen cross-linking, and gene expression. We found that alveolar mucosa is primarily composed of fibrillar collagens and the collagen content is higher than attached gingiva. The content of type III relative to type I collagen was higher in alveolar mucosa when compared with attached gingiva. The collagen cross-linking pattern also was distinct between the two tissues demonstrating that alveolar mucosa contained fewer reducible cross-links but more nonreducible cross-links in comparison to attached gingiva. The mRNA expression level of type I collagen in alveolar mucosa was significantly lower than that of attached gingiva. These results indicate that alveolar mucosa is a fibrillar collagen-rich tissue and, in comparison to gingival tissue, remodels slowly.

Medication-related osteonecrosis of the jaw; what should we do as prosthodontists?

Medication-related osteonecrosis of the jaw (MRONJ), which is a rare but severe impairment of oral wound healing in patients taking antiresorptive drugs, including bisphosphonates (BPs) and denosumab, mainly occurs after tooth extraction [1]. Due to their pharmacological action, oral and intravenous BPs have been widely used to treat osteoporosis, bone metastases of solid tumors, multiple myeloma and Paget’s disease in Japan and other countries [2]. Denosumab, which is a human monoclonal antibody against the receptor activator of nuclear factor-kB ligand (RANKL), has recently been approved for osteoporosis and malignant therapies in Japan. Denosumab is also antiresorptive, but has a different pharmacological action than BPs in that it binds to RANK, and targets both bone resorbing osteoclasts and pre-osteoclasts [3].

Characterization of the bone matrix and its contribution to tooth loss in human cadaveric mandibles.

Abstract Objective. It is uncertain as to what extent the major bone matrix constituents, mineral and collagen, show inter-individual variation and dependence on age and sex in jawbones. The purpose of this study was to clarify this uncertainty using cadaveric mandibles and investigate the association of bone matrix with the number of existing teeth. Materials and methods. Cortical bone samples (1 × 1 cm) collected from the mental of 48 cadaveric mandibles (27 men and 21 women; age range = 56–93 years and 63–103 years, respectively) were used to quantify three bone matrix indices: mineral content, collagen content and extent of lysine hydroxylation of collagen. Associations with age and comparisons by sex were evaluated based on bone matrix indices and the numbers of existing teeth. The numbers of existing teeth were compared between the groups showing low and high bone matrix index values. Results. A great amount of inter-individual variation was seen in all bone matrix indices. No bone matrix indices were associated with age, while the number of existing teeth was negatively associated with age. The bone matrix indices and number of existing teeth did not differ by sex. The number of existing teeth was nearly twice as high in the group showing high collagen content as in the low collagen group; however, an analysis of covariance showed a significant inter-group difference not from bone matrix indices, but rather from age. Interestingly, in comparison to femoral collagen, mandibular collagen showed lower lysine hydroxylation, which can represent an aspect of bone quality. Conclusions. Mandibular bone matrix shows great inter-individual variation and is independent of age and sex, but did not show as strong a relationship with tooth loss as age. Even so, mandibular collagen may represent a unique characteristic of bone matrix and deserves to be further investigated.