In vitro expansion of cells is often limited by stress-induced premature senescence, and DNA double strand breaks are the most relevant damage related to the irreversible cell cycle arrest caused by oxidative stress. Recently, it has been shown that DNA damaging checkpoint proteins are activated by phosphorylation at the sites of DNA double strand breaks caused by ionizing radiation. ATM protein, which is the product of the gene mutated in radiation sensitive disorder called ataxia-telangiectasia (AT), functions as the primary sensor for DNA double strand breaks, and when visualized with an antibody recognizing phosphorylated ATM at S1981, phosphorylated ATM appears as nuclear foci after irradiation. The foci are induced dose-dependently, and the number of phosphorylated ATM foci is well correlated with the estimated number of DNA double strand breaks, providing an unique and sensitive tool for the measurement of DNA double strand breaks at the physiological level in situ.

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Tissue engineering, first conceived in the 1980s, is now drawing tremendous social attention as the research progresses. Scaffold materials used to engineer tissues have traditionally been synthetic polymers, biocompatible porous inorganic materials and purified extracts of natural extra-cellular matrices (ECMs). To date, there are no biomaterials in clinical use that possess both the safety of the polymers and ECM-like 3-dimensional environments for cells.
A group of self-assembling synthetic peptides ("PuraMatrix^TM"), developed at MIT are composed solely of natural amino acids found in organisms. These peptides self-assemble into nano-fibers of approximately 10 nm in diameter under physiological conditions, resulting in formation of hydrogel. In this hydrogel, many cell types are shown to adhere and proliferate, and injection of the gel with or without cells, promotes regeneration of tissues such as bone, brain and cardiac tissue. This peptide hydrogel is shown to be safe by animal safety tests and may become available as a medical device for clinical application soon.

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In this study, the wavelength of a CO₂ laser was modified to 9.45µn;m (Modi-CO₂ laser) and the cutting efficiency of Modi-CO₂ laser was evaluated. We used the freshly extracted human molars without carious regions. The dentin surface of the thawed teeth was polishing with alumina (0.05 mm). Modi-CO₂ laser was irradiated by TEA-CO₂ laser. Modi-CO₂ laser was irradiated on the polished dentin surface under the irradiation conditions of 1 MW/pulse and 1, 5, 10 and 50 pulses. The pulse width of one pulse was set to 100 ns. The Modi-CO₂ laser-irradiated dentin surfaces were Au-spattered and were observed by an electron surface roughness analyzer. The volume lost by the irradiation of the laser was calculated from the diameter and the depth of cavity. The relationship between the lost volume and the irradiation energy was statistically analyzed by one-way ANOVA and Scheffe's test (p<0.05). No measurable loss of dentin was detected with Modi-CO₂ laser-irradiation of 1 and 5 pulses. The lost volumes of dentin with 10 and 50 pulses were 143333 and 342333 mm³. The lost volume by the irradiation of Modi-CO₂ laser significantly increased with an increase of the pulse of Modi-CO₂ laser.

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The present study was performed to examine the effects of acidic phosphate fluorine (APF) solution on the surface layer of dentin using an atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). Twenty human teeth were cut to create the dentin discs with the diameter of 3 mm. Half of the discs were highly polished. Another half of the discs were highly polished and then immersed in a demineralizing solution (pH 5.0) for 24 hours to produce the subsurface lesions. The demineralizing solution consisted of 0.1 M lactic acid, 0.2% carbopol and 50% saturated hydroxyapatite. All specimens were treated in 10 ml APF solution (2.0%) for 4 minutes. The surface of each specimen was observed with an AFM and the specimens were subjected to scans with XPS. The surface of APF-treated polished dentin was flat without closure of dentinal tubes. The crystals in the APF-treated polished dentin were more globular than polished dentin. The surface of the APF-treated demineralized dentin was rough compared to the polished dentin. The crystals were square, and their porositys were expanded. The APF treatment reduced the roughness of the surface and the crystalline porosity by dense gathering of globular and oval crystals. The relative concentration of F was increased by the APF treatment. The F/Ca atomic ratio was 0.02±0.02 in the polished dentins, 1.88±0.09 in the APF-treated polished dentins, and 1.95±0.11 in the APF-treated demineralized dentins. These results indicated that fluorine-reaction products were generated by the APF treatment of the polished dentin and demineralized dentin.

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In the present study we attempted to observe the 3-dimensional morphology during the process of bone calcification at peri-implant tissue, with the use of microcomputed tomography (micro-CT). Six titanium implants were placed in the maxillary bone of 3 beagle bogs. At 4, 8 and 12 weeks after implantation, the dogs were sacrificed and the interface between new bone formation and implants in undecalcified blocks was investigated using micro-CT.
At 4 weeks after implantation, there was little bone formation between host bone and the implant. At 8 weeks after implantation, new bone formation was seen as an extension of calcification from host bone. At 12 weeks after implantation, there were increases of bone volume at the peri-implant tissue. Micro-CT could be used to observe the necked eye figures and quantify the bone remodeling system at peri-implant tissue. This technique has the advantage of enabling 3-dimensional analysis of the interface between the modeling bone and the titanium implant following surgery. In addition, the micro-CT technique allowed examination at higher magnification in this area.

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Bone cells are regulated by interaction with growth factors and components of the extracellular matrix. Syndecans are transmembrane heparan sulfate proteoglycans known to bind both other extracellular matrix molecules and certain growth factors. In this study using quantitative real-time RT-PCR, we investigated the expression of the syndecan family in normal human osteoblasts exposed to interleukin (IL)-1β as a bone resorptive agent. RT-PCR analysis demonstrated the mRNA expression of syndecan-1, -2 and -4 in normal human osteoblasts. When cells were incubated with IL-1β, there were significant decreases in mRNA levels for syndecan-1 and -2 at 24 h compared with time-matched controls. In contrast, the expression of syndecan-4 in IL-1β-stimulated osteoblasts markedly increased at 6 h followed by a decrease at 24 h. These results demonstrate that syndecan-1, -2 and -4 are synthesized in human osteoblasts, and syndecan-4 gene transcription is rapidly responsive to an inflammatory mediator.

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