歯科医学

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ビスフェノールA(Bisphenol A;以後BPAと略す.)は,歯科材料をはじめポリカーボネイトの原料として広く使われる人工化学物質であり,環境ホルモンの1つである.BPAの耐用1日摂取量(50μg/kg/day)は多くの生殖毒性試験に基づいて定められている.本研究では中枢への作用に基づいた評価法を検討するため,性的二型行動を指標にした微量BPA曝露の影響を調べた.耐用1日摂取量以下の極微量BPAを妊娠期および授乳期の母ラットに経口投与し,生まれた仔ラットの成長後にオープンフィールド試験における活動性および探索行動を調べ,さらに高架十字迷路試験で不安レベルを,受動的回避学習試験で回避学習能を観察した.活動性および探索行動では対照群で性的二型(性差)を示し,BPA曝露により探索行動の性差のみが消失した.高架十字迷路試験におけるオープンアーム進入回数比ならびに回避学習能において,対照群で確認された性差はBPA曝露群でも同様に確認され,性差の撹乱は認められなかった.オープンフィールド試験における探索行動は性的二型行動の評価法として鋭敏な指標と考えられる.

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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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