Shikaigaku

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Bisphenol A (BPA) is an environmental endocrine disrupter that is used in polycarbonate plastics, dental prostheses and dental sealants. Most studies on BPA have dealt with its effect on reproductive systems. A reference dose of 50μg/kg/day has been established based on data of reproductive toxicity. Our study focused on the central nervous system and sexually dimorphic behavior of rats. Both of these factors are sensitive to environmental chemical substances. BPA at 0.1ppm in drinking water was applied to dams during prenatal and postnatal periods. The offspring were examined in the open-field test, elevated plus maze test and passive avoidance test. Both pre- and postnatal exposure to BPA mainly affected male rats and abolished sex differences in exploratory behavior in the open-field test. However, the BPA impact on this sexual dimorphism was not particularly significant when the exposure was postnatal. Avoidance learning and results of the elevated plus maze test were not affected. These results suggest that sexually dimorphic open-field behaviors are highly sensitive to environmental endocrine disrupters.

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It is well established that osteoclast differentiation/activation is involved in orthodontic tooth movement at compression sites. However, the mechanism of osteoclast differentiation/activation in orthodontic tooth movement remains unclear. Nitric oxide (NO) has been reported to play a crucial role in bone remodeling induced by mechanical loading, and several reports have shown that inhibition of NO syntheses prevents orthodontic tooth movement in animal models. We investigated whether osteoclast differentiation can be induced by NO in vitro. We found that sustained release of NO by NOC-18 induces osteoclast differentiation of not only RAW264 cells but also bone marrow macrophages, and that the inhibition of ERK and activation of p38 MAPK may be involved in NOC-18-induced osteoclast differentiation.

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We examined the metallic artifacts created in magnetic resonance images (MRI) of multibracket appliances using steel, resin and ceramic brackets placed on plastic study models. The steel wires placed were plane archwire, archwire bended L-loops and archwire bended keyhole loops. We used a 1.5 Tesla super-conductive magnetic resonance imaging (MRI) machine to make 3 sequences of images: spine echo T1 weighted images, fast gradient echo for three-dimensional T2 weighted images, and fluid attenuated inversion recovery images. A model that adapted steel brackets, archwire bended keyhole loops, palatal bar and steel ligatures produced the largest metallic artifacts, while ceramic brackets, archwire bended L-loops, and elastic ligatures produced the smallest metallic artifacts. These findings suggest that clinicians should be aware of metallic artifacts in MRI caused by multibracket appliances.

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It is well known that because biofilm-forming bacteria produce a large amount of exopolysaccharides (EPS), they can cause chronic or persistent infections. However the genes associated with EPS production remain poorly understood. To identify gene(s) responsible for EPS production, we performed random mutagenesis against a clinical isolate, Actinomyces oris strain K20, which has considerable ability to continuously produce EPS. SEM observation revealed five EPS production-deficient mutants. One had a transposon insertion within a gene that encodes polysaccharide deacetylase. Extensive analysis around this gene showed the existence of several open reading frames predicted to be associated with the biosynthesis of sugar. Our findings indicated this gene might be implicated in EPS production in A. oris strain K20.

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