The dentition in extant holocephalans (Chondrichthyes) comprises three pairs of continuously growing dental plates, rather than the separate teeth characterizing elasmobranchs. We investigated how different types of dentine in these plates, including hypermineralized dentine, are arranged, and how this is renewed aborally, in adult and juvenile dentitions of Harriotta raleighana (Rhinochimeridae). Individual plates were analysed using x-ray computed tomography (μCT), scanning electron microscopy (SEM) in back scattered mode with energy dispersive X-ray (EDX) analysis, and optical microscopy on hard tissue sections. Harriotta dental plates are made entirely of dentine tissue, mostly as trabecular dentine, bone itself being absent. Hypermineralized dentine forms in restricted ovoid and tritor spaces within trabecular dentine, inside a shell of outer and inner dentine layers. Trabecular dentine is ubiquitous but changes to sclerotic osteodentine near the oral surface by increasing density, remaining less mineralized than the hypermineralized dentine. All structures are renewed aborally, within a vascular dental pulp, a tissue suggested to be a source of stem cells for tissue renewal. Ca density profiles and concentrations of Mg, P, and Ca ions reveal extreme differences in the level and type of mineralization. Early mineralization in ovoids and tritors has very high levels of Mg, then a sudden increase in mineralization to a high total mineral content, whereas there is gradual change in trabecular dentine, remaining at a low level. Hypermineralized dentine fills the prepatterned ovoid, rod and tritor spaces, early at the aboral surface within the trabecular dentine. Deposition of the hypermineralized dentine (HD, proposed as new specific name, whitlockin replacing pleromin) is from surfaces that are lined with large specialized odontoblasts, (whitloblasts, instead of pleromoblasts) within cell body spaces connecting with extensive, ramifying tubules. Early mineralization occurs amongst this maze of tubules that penetrate far into the dentine, expanding into a mass of saccules and membranous bodies, dominating in the absence of other organic matrix. This early stage has hydroxyapatite, also significantly rich in Mg, initiated as a poorly crystalline phase. In the hypermineralized dentine, formation occurs as clusters of variably shaped crystals, arising from a sudden phase transition. In the hypermineralized dentine, high MgO + CaO + P2O5 suggests that almost pure Mg containing tricalciumphosphate (MgTCP: (ß-Ca3(PO4)2) (whitlockite) is present, with little or no hydroxyapatite. Serial replacement of tritors and ovoids is suggested to occur within the dental plate, probably representing a relic of patterning, as classically found in elasmobranch dentitions.

中文翻译：

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holocephalan Harriotta raleighana (Chondrichthyes) 牙板中的生长和矿物学：新的牙本质和保守的图案相结合，创造出独特的软骨鱼牙列

现存的全头动物（软骨鱼纲）的牙列由三对连续生长的牙板组成，而不是表征弹性鳃的单独牙齿。我们研究了这些板中不同类型的牙本质，包括高度矿化的牙本质，是如何排列的，以及它们是如何在 Harriotta raleighana (Rhinochimeridae) 的成年和幼年牙列中进行异位更新的。使用 X 射线计算机断层扫描 (μCT)、具有能量色散 X 射线 (EDX) 分析的背散射模式的扫描电子显微镜 (SEM) 和硬组织切片的光学显微镜对单个板进行分析。Harriotta 牙板完全由牙本质组织制成，主要是小梁牙本质，骨骼本身不存在。高度矿化的牙本质在小梁牙本质内受限的卵形和三叉骨空间中形成，在内外牙本质层的外壳内。小梁牙本质无处不在，但随着密度的增加，在口腔表面附近变成硬化的骨牙本质，与高度矿化的牙本质相比矿化程度较低。在血管牙髓内，所有结构都在腹腔内更新，这种组织被认为是组织更新的干细胞来源。Ca 密度分布和 Mg、P 和 Ca 离子的浓度揭示了矿化水平和类型的极端差异。卵形体和三棱体的早期矿化具有非常高的 Mg 水平，然后矿化突然增加至高总矿物质含量，而小梁牙本质逐渐变化，保持在低水平。高度矿化的牙本质在小梁牙本质内的远侧表面早期填充预先形成的卵形、杆状和三叉形空间。高矿化牙本质（HD，建议作为新的特定名称，whitlockin 取代 pleromin）的沉积来自与广泛的分枝小管连接的细胞体空间内衬有大型特化成牙本质细胞（成牙本质细胞，而不是成牙本质细胞）的表面。早期矿化发生在这个迷宫般的小管中，这些小管深入牙本质，扩展成大量的球囊和膜状体，在没有其他有机基质的情况下占主导地位。这个早期阶段有羟基磷灰石，也显着富含镁，开始时是一个结晶度差的相。在高度矿化的牙本质中，由于突然的相变，形成了形状各异的晶体簇。在高矿化牙本质中，高 MgO + CaO + P2O5 表明几乎纯 Mg 含有磷酸三钙（MgTCP：(ß-Ca3(PO4)2) (白磷灰石) 存在，几乎没有或没有羟基磷灰石。建议在牙板内连续更换tritors和卵形，这可能代表了模式的遗迹，如在弹性鳃牙列中经典发现的那样。