Important roles of odontoblast membrane phospholipids in early dentin mineralization

The objective of this study was to first identify the timing and location of early mineralization of mouse first molar, and subsequently, to characterize the nucleation site for mineral formation in dentin from a materials science viewpoint and evaluate the effect of environmental cues (pH) affecting early dentin formation. Early dentin mineralization in mouse first molars began in the buccal central cusp on post-natal day 0 (P0), and was first hypothesized to involve collagen fibers. However, elemental mapping indicated the co-localization of phospholipids with collagen fibers in the early mineralization area. Co-localization of phosphatidylserine and annexin V, a functional protein that binds to plasma membrane phospholipids, indicated that phospholipids in the pre-dentin matrix were derived from the plasma membrane. A 3-dimensional in vitro biomimetic mineralization assay confirmed that phospholipids from the plasma membrane are critical factors initiating mineralization. Additionally, the direct measurement of the tooth germ pH, indicated it to be alkaline. The alkaline environment markedly enhanced the mineralization of cell membrane phospholipids. These results indicate that cell membrane phospholipids are nucleation sites for mineral formation, and could be important materials for bottom-up approaches aiming for rapid and more complex fabrication of dentin-like structures

ニホン ドウブツエン スイゾクカン キョウカイ ノ カンリ スル ユーラシア カワウソ ノ イデンテキ タヨウセイ ト ハンショク ケイカク

ユーラシアカワウソ(Lutra lutra)はユーラシア大陸に広く分布する中型食肉目である。本種には11の亜種がおり,欧州亜種L. l. lutra,東南アジア亜種L. l. barang,中国亜種L. l. chinensis などが国内外の動物園や水族館で飼育されている。欧州の動物園や水族館にはA-line(L. l. lutra)とB-line(L. l. lutraとL. l. barangが交雑した可能性がある系統)という2つのlineが存在し,日本の動物園や水族館にも導入されている。本来は同じ亜種内で繁殖がおこなわれるが,日本では本種の個体数が少ないためA-lineとB-lineで繁殖がおこなわれている。実際にB-lineが東南アジア亜種の遺伝子を持っているか評価がおこなわれ,B-lineとA-lineの間に違いがあることが示された。ただし先行研究では,解析配列が307bpと短いことが問題として上げられる。本研究ではミトコンドリア(mt)DNA Cytochrome bの全長配列(1140bp)をA-line,B-line各1個体,中国亜種2個体から決定し,先行研究で決定されたB-lineの配列を含む4配列を加えて配列比較,系統解析をおこなった。その結果,A-line,B-lineそれぞれが特徴的な変異サイトを示し,系統解析では先行研究と同じようにB-lineは中国亜種とクレイドを形成し,A-lineは欧州亜種独自のクレイドを形成した。よって解析したB-lineのmtDNAは東南アジア亜種に由来する可能性がある。2015年現在,日本のB-line個体は全て本研究で解析したB-lineの子や孫である。亜種間交雑が示唆された国内のB-lineは,本種の繁殖・維持に活用できるが,A-lineや中国亜種の系統維持に活用することはできない。Eurasian otter (Lutra lutra) is a mid-sized species belonging to the order Carnivora and is distributed across a wide area of the Eurasian continent. This species comprises 11subspecies. The European subspecies (L. l. lutra), the Southeast Asian subspecies (L. l. barang), and the Chinese subspecies (L. l. chinensis) are reared in European and Japanese zoos and aquariums. Among these, the European facilities rear two lines, which were named A-line (L. l. lutra) and B-line (this is likely a crossbreed of L. l. lutra and L. l. barang); the Japanese facilities introduced these two lines. The mitochondrial (mt) DNA partial cytochrome b (cytb) sequence (307bp) of the A- and B-lines detected previously have shown slight but characteristic differences between the two lines. However, the previous study had limitations, as only one sample of the B-line was considered and the sequence was found to be short. Although, typically, breeding involves mating of individuals within the same subspecies, the A- and B-lines were crossbred in the Japanese facilities, which is likely because only small numbers of the Eurasian otter were reared in these facilities, thereby making cross-breeding imperative to the conservation of Eurasian otter in this country. In this study, we determined the complete cytb sequence (1140bp) from one individual each of the A- and B-lines, and two individuals of the Chinese subspecies. These sequences were compared and subjected to phylogenetic analysis, along with four individuals of Eurasian otter (which includes one B-line individual). The B-line individual showed diagnostic nucleotides at two positions, whereas the A-line individual showed diagnostic nucleotides at four positions. In the phylogenetic tree, two B-line individuals formed a monophyletic group with the two individuals of Chinese subspecies, and an A-line individual formed another monophyletic group with the other European individual. These results suggest that mtDNA sequence of B-line was derived from some Asian subspecies, and it differed from the A-line sequence (European subspecies). Moreover, because these results suggest that hybridization between the European subspecies and some Asian subspecies occurred in the B-line, the breeding program involving B-line individuals is not appropriate to the conservation of subspecies-specific strains

Influence of preliminary extrusion conditions on the superplastic properies of a magnesium alloy processed by ECAP

The microstructures and properties of a two-phase Mg–8% Li alloy were evaluated in three different conditions: after casting; after casting followed by extrusion at different temperatures and speeds; and after casting, extrusion and processing by ECAP for four passes at room temperature using a die with a channel angle of 135°. The results show extrusion introduces significant grain refinement and there is additional refinement in ECAP. In tensile testing, the elongations to failure increase with decreasing extrusion temperature, but are essentially independent of the extrusion speed. The ductilities are low in the cast condition, intermediate in the extruded condition and high after extrusion and ECAP. For the last condition, an exceptionally high elongation of 1780% was achieved at a testing temperature of 473 K. It is shown that it is advantageous to use a die with a channel angle of 135° because it permits pressing at room temperature where grain growth is limited

Improving the superplastic properties of a two-phase Mg–8% Li alloy through processing by ECAP

Significant grain refinement was achieved in a cast Mg–8 mass% Li alloy through processing by equal-channel angular pressing (ECAP) using a die having an internal channel angle of 110° and a pressing temperature of 473 K. Following extrusion and subsequent ECAP through two passes, the alloy exhibited excellent superplastic properties including a maximum elongation of ~970% at 473 K when using an initial strain rate of 1.0 × 10?4 s?1. The strain rate sensitivities under the optimum superplastic conditions were measured as m ? 0.4–0.6. The maximum elongation achieved in this investigation is very high by comparison with other Mg alloys tested in tension at similar temperatures and strain rates

Biomechanical Evaluation of Ti-Nb-Sn Alloy Implants with a Low Young’s Modulus

Dental implants are widely used and are a predictable treatment in various edentulous cases. Occlusal overload may be causally related to implant bone loss and a loss of integration. Stress concentrations may be diminished using a mechanobiologically integrated implant with bone tissue. The purpose of this study was to investigate the biomechanical behavior, biocompatibility and bioactivity of a Ti-Nb-Sn alloy as a dental implant material. It was compared with cpTi. Cell proliferation and alkaline phosphatase (ALP) activity were quantified. To assess the degree of osseointegration, a push-in test was carried out. Cell proliferation and ALP activity in the cells grown on prepared surfaces were similar for the Ti-Nb-Sn alloy and for cpTi in all the experiments. A comparison between the Ti-Nb-Sn alloy implant and the cpTi implant revealed that no significant difference was apparent for the push-in test values. These results suggest that implants fabricated using Ti-Nb-Sn have a similar biological potential as cpTi and are capable of excellent osseointegration