The basic principle of bone induction for tissue engineering is to use stem cells, growth factors and organic matrix. KUSA/A1 cell is an example of bone marrow stromal stem cell, capable of differentiating into osteoblasts, chondrocytes and myotubes under inducing conditions. It has been reported that mature KUSA/A1 osteoblasts cultured in osteogenic condition, were able to induce a few bone formation in collagen hybridized PLGP sponge in vivo. This may be due to their low proliferation potential thereby not being able to obtain sufficient number of cells to promote large tissue repair. Because of this, in order to use KUSA/A1 cells with high cell proliferation activity to induce large amount of new bone, we evaluated whether KUSA/A1 cells in non-induction condition will maintain their immature stage. The result demonstrated that KUSA/A1 cells cultured in α-MEM maintained their immature stage in vitro. We further examined the osteoblastic differentiation under the influence of the host microenvironment in intraperitoneal diffusion chamber. The results indicated that immature KUSA/A1 cells in vivo cell culture differentiated into osteoblasts and produced mineralized bone-like tissue. Finally, we evaluated the effect of honeycomb scaffold to produce abundant bone formation using KUSA/A1 cells implanted in subcutaneous tissues of SCID mice. 1x10⁶ KUSA/A1 cells with honeycomb scaffold showed abundant new bone formation. While, 5x10⁶ KUSA/A1 cells alone showed only few small islands of new bone formation. This study support that KUSA/A1 cell is a good candidate as stem cells for basic research in bone tissue engineering.

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Bone plays a pivotal role in storing calcium and phosphate in vertebrates. This tissue is maintained by the balance of bone formation and bone resorption. Osteoblast-lineage cells, consisting of osteoblasts, osteocytes and bone lining cells, are engaged in bone formation. Bone resorption is mediated by osteoclasts. Recent research revealed that receptor activator of NF-κB (RANK)-RANK ligand (RANKL) mechanism is essential for the differentiating and activating osteoclasts. Osteoblast-lineage cells regulate bone resorption via the expression of RANKL and osteoprotegerin (OPG), a decoy receptor for RANKL. Additionally, osteoblast-lineage cells participate in degradation of bone matrix by secreting MMP-13. Thus, bone remodeling is achieved by the harmonized orchestration of osteoblast-lineage cells and osteoclast-lineage cells.

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Immunolocalization of heparan sulphate(HS) and heparanase was evaluated in benign and malignant odontogenic tumors in order to know whether these molecules have potential roles in odontogenic tumorigenesis. Archival formalin-fixed, paraffin-embedded tissues of 6 human tooth germs, 7 adenomatoid odontogenic tumors, 10 ameloblastic fibromas, 20 ameloblastomas and 4 ameloblastic carcinomas were subjected to immunohistochemical staining using antibodies to HS, heparanase and BMP-4. HS was ubiquitously localized in tooth germ but heparanase and BMP-4 were observed in limited areas only. In benign epithelial tumors such as ameloblastoma and adenomatoid odontogenic tumor, these molecules were localized in neoplastic epithelium but in ameloblastic fibroma, positive reactions were observed in both epithelial and mesenchymal cells. Stromal localization of HS and BMP-4 accompanied by intense immunoexpression of epithelial heparanase was observed in ameloblastic carcinoma, and this may represent the malignant progression of ameloblastoma to ameloblastic carcinoma. Stronger intensity and more diffuse localization of heparanase in odontogenic tumors compare to that of human tooth germ was the most significant finding. Taken together, the results inferred that heparanase may be responsible for the growth and progression of odontogenic tumors by modulating the availability and function of HS binding growth factors and the derangement in immunoexpression and localization of HS and heparanase molecules may have important roles in progression of malignant odontogenic tumors.

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We encountered a patient on long-term oral corticosteroids for systemic lupus erythematosus, who did not complain of pain during caries treatment. Since the patient had no subjective sense of dental pain, all her remaining teeth became stumps, and total tooth extraction was conducted 25 years after presentation. We examined her premolar stumps histopathologically and obtained the following findings: 1. the dental pulp was narrowed in nearly all samples; 2. odontoblasts were not observable; 3. regions with dentinal tubules forming lamellae and regions with fibrotic dentinal tubules were observed. 4. fibrosis of the entire dentin was observed in some regions. 5. nerve fibers stained by anti-neurofilament protein antibody were observed in the dental pulp cavity, but the nerve fibers appeared degenerate and no nerve fiber endings were observed.

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Human bone marrow mesenchymal stem cells (hMSCs), one of the tissue stem cells, have the ability to differentiate into adipocytes, osteoblasts or chondrocytes, leading to the attempt to apply these stem cells to regeneration of bone and cartilage. To analyze characteristics of these cells and explain pluripotency of hMSCs, we analyzed gene expression profiles of hMSC clones by using DNA chips that contain over 10,000 genes per chip. We also analyzed their proliferation rates and cell surface markers. As a result, these hMSC clones showed various proliferation rates indicating that hMSCs contains multiple types of cells in their population. Furthermore, analysis of surface markers, especially analysis of CD34 and CD44 showed that these stem cells are not hematopoietic stem cells but mesenchymal origin. Profiling of gene expression by using DNA chip showed that several genes were specifically expressed in hMSCs, and the highest expression was observed in clone no.12 showing that this clone possesses unique characters as a MSC applicable to regeneration research and regenerative medicine.

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We have been studying the relationships between results of osteoporosis screening examinations and those of dental health checkups, and have reported the relationship between number of remaining teeth and bone density in the calcaneus (%YAM). Further, that relationship was also examined using Functional Tooth Evaluation Score (FTES) results, which we found able to quantify and numerically express oral conditions. In the present study, we examined the relationship between the mean results of FTES and bone density in the calcaneus by age, and used the results for clinical application. The subjects for this study were 235 women of 30's-70's. Following are the results for subjects aged 50 - 64 years old.
(1) The tendencies for changes in mean FTES and bone density in the calcaneus by age were very similar. Mean FTES and mean bone density in the calcaneus showed a positive correlation. (p<0.01).
(2) Subjects who demonstrated a lower FTES than expected on the basis of the age were referred to an orthopedic specialist for measurements of bone density, and some were diagnosed with osteoporosis. As a result, our findings suggested that FTES can be utilized for screening of osteoporosis.

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