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The aim of this study was to examine the effect of centrifugal force on rat bone marrow osteoblast-like cells (RBM) in vitro. RBM were seeded and cultured for 2 days. Centrifugal forces were added to the cells in the culture dishes using a centrifuge for 20 min either at 600 rpm or 4,800 rpm. The cells without centrifugation were used as control. The expression of HSP27 mRNA of both experimental groups after addition of centrifugal force for 3 hrs was significantly up-regulated compared with the control group. In the 4,800 rpm groups, the cells showed contracted shapes compared to the controls and the 600 rpm groups after treatment with centrifugal force. The maximum height of each cell in the control group was 2.00 ± 0.33 μm. The maximum height of each cell in the 600 rpm group was 1.50 ± 0.23 μm, and in the 4,800 rpm group it was 1.13 ± 0.23 μm. The proliferation ratio in the 4,800 rpm group at day 3 was significantly higher than in the other group. The expression of type I collagen and alkaline phosphatase (ALP) mRNAs in both experimental groups increased at earlier time periods compared to the control groups. ALP activity revealed no significant difference between the experimental groups and the control group. A centrifugal force of 4,800 rpm might promote the proliferation and early differentiation of rat bone marrow cells.

The purpose of this study was to evaluate the effects of nicotine on Malassez' epithelial rest (MER) cells which are thought to maintain the homeostasis of the periodontal ligament. MER cells obtained from porcine periodontal ligament were cultured for 7 days, after which nicotine was added to the culture medium at concentrations of 0.03 μM, 0.15 μM or 0.2 μM. Cells cultured without nicotine were used as controls. Cell proliferation and expression of mRNAs encoding heat shock protein 70 (HSP70) and vascular endothelial growth factor (VEGF) were analyzed to evaluate the effects of nicotine. The cell proliferation ratios of all nicotine-treated groups were significantly lower than the control group on day 7. The expression of HSP70 mRNA in all nicotine-treated groups was higher than in the control group. The expression of VEGF mRNA in all nicotine-treated groups at all times examined tended to be lower than in the control groups. In conclusion, nicotine affects MER cells by increasing mRNA expression of HSP70, but decreasing that of VEGF.

Ballistic muscle training leads to hypertrophy of fast type fibers and training for endurance induces that of slow type fibers. Numerous studies have been conducted on electrical, extending and magnetic stimulation of cells, but the effect of centrifugal force on cells remains to be investigated. In this study, we investigated the effect of stimulating cultured myoblasts with centrifugal force at different speeds on cell proliferation and myosin heavy-chain (MyHC) mRNA expression in muscle fiber. Stimulation of myoblasts was carried out at 2 different speeds for 20 min using the Himac CT6D, a desk centrifuge, and cells were observed at 1, 3 and 5 days later. Number of cells 1 and 5 days after centrifugal stimulation was significantly larger in the 62.5 x g and 4,170 x g stimulation groups than in the control group. Expression of MyHC-2b mRNA 1 day after centrifugal stimulation was significantly higher in the 2 stimulation groups than in the control group. Almost no expression of MyHC-2a was observed in any group at 1 and 3 days after centrifugal stimulation. However, 5 days after stimulation, MyHC-2a was strongly expressed in the 2 stimulation groups in comparison to the control group. Three days after centrifugal stimulation, expression of MyHC-1 was significantly higher in the 2 stimulation groups than in the control group. The results of this study clarified the effect of different centrifugal stimulation speeds on muscle fiber characteristics, and suggest that centrifugal stimulation of myoblasts enhances cell proliferation.

PURPOSE A mouthguard can protect stomatognathic systems from traumatic damage. However, severe occlusal wear of teeth and loss of teeth have often been found in players clinically. These problems might originate in strong clenching during sports. Although it is thought that a mouthguard may be effective for these types of clenching, the relation between mouthguards and clenching has not been sufficiently examined. In this study, the effect of a mouthguard (Drufosoft 3mm, EVA) on tooth distortion caused by clenching was measured and examined at three different clenching strengths. METHODS As a test tooth, a lower first molar was selected. A strain gauge applied to the outer surface of the buccal cusp was used to measure the distortion. A muscle balance monitor (GC) was used to regulate clenching strengths (10, 50, and 100%). The maximum-effort clenching without a mouthguard was assumed to be the 100% clenching strength. Measurements were conducted with or without mouthguard. A maximum value during clenching was assumed to be date of distortion by using analytical software AcquKnowledge (BIOPAC System Inc.). Statistical analysis software SPSS (SPSS Japan Inc.) was used for the Mann-Whitney test. RESULTS 1. The tooth distortion by clenching, regardless of the presence of the mouthguard, increased as clenching power strengthened, from 10, 50 to 100%. 2. The tooth distortion, regardless of strength of clenching, was decreased by wearing the mouthguard in all subjects. At 50 and 100% clenching, it was decreased significantly by the mouthguard in all subjects. CONCLUSIONS Mouthguards decreaseed the tooth distortion caused by clenching. Therefore, a mouthguard may prevent not only traumatic injuries in contact sports but also damage to teeth and periodontal tissues and so on, which occur due to frequent strong clenching in many sports.

The principle of whole-body counting is widely applied to various fields of science. Much emphasis has so far been laid on the detection of a very small quantity of radioactivity, thus strenuous efforts having been made to improve sensitivity and energy resolution of equipments. In order to accomplish the purpose of radiation protection effectively, however, the following three points become more important. Namely, (1) Clearifying the role of whole-body counting in the radiation protection service.(2) Giving the whole-body counter the function as an individual monitor of internal exposure.(3) Utilizing the whole-body counter more easily and frequently, feeding the result back to the radiation protection service rapidly.The present paper gives some basis for the argument that a simplified whole-body counter can meet these requirements satisfactorily, and that effective and economical radiation protection can readily be accomplished by this simplification. The basic properties required of the simplified whole-body counter for the monitoring purpose are considered in view of efficiency of detectors, its mechanism, and the way of utilizing it in the routine monitoring program. As an example, the paper describes the outline of the simplified whole-body counter intended to be installed in a certain nuclear power station.