Boyde Alan, Tyler Nicholas J C
Dental Physical Sciences Unit, Institute of Dentistry, Queen Mary University of London, London, UK.
Centre for Saami Studies, UiT the Arctic University of Norway, Tromsø, Norway.
J Anat. 2025 Jan;246(1):160-167. doi: 10.1111/joa.14135. Epub 2024 Sep 5.
Counting growth layers in dentine and/or secondary cementum is widely used for age determination in wild mammals but the underlying seasonal changes in the structure and degree of mineralisation of dental tissue have not been well characterised. We embedded first (m1) and second (m2) mandibular permanent molar teeth from a 12-year-old female Svalbard reindeer (Rangifer tarandus platyrhynchus) in PolyMethylMethAcrylate (PMMA), prepared cut and polished surfaces coated with evaporated carbon and used 20 kV back-scattered electron imaging in a scanning electron microscope (BSE-SEM) to study aspects of dental tissue structure which depend on the degree of mineralisation at the micron and sub-micron scale. BSE-SEM revealed differences between the mineral content of growth layers (annulations) in the secondary cementum and the primary and secondary dentine, the latter, incidentally, still forming at death in m1. Wide bands of less well mineralised tissue formed in the cementum during active appositional phases. Thin, denser bands formed by maturation-mineralisation of existing tissue when growth slowed in winter. This maturation mimics the processes seen in lamellar bone and articular cartilage. Counter to previous suggestions, there was evidence of substantial resorption and repair of the secondary cementum and of formation of dentine throughout life. Secondary dentine is layered by mineral content like cementum. In the crown, this was mainly tubular dentine with well-marked interglobular dentine layers. In the lower pulp chamber and root, it was largely without tubules. Substantial non-mineralised spaces found at the cement-dentine junction in the root apical regions in m2 represent inclusions of the Hertwig's Epithelial Root Sheath (HERS) or the Epithelial Rests of Malassez (ERM) between the two tissues, a phenomenon which has previously only been identified in Muridae. The anatomical changes which result in the formation of the incremental lines (annulations) in dental tissues of reindeer, identified here for the first time at the micrometre level, are likely to be common across most if not all long-lived species of mammals living in seasonal environments.
通过计算牙本质和/或继发性牙骨质中的生长层来确定野生哺乳动物的年龄，这一方法被广泛应用，但牙齿组织矿化结构和程度的潜在季节性变化尚未得到充分表征。我们将一只12岁雌性斯瓦尔巴德驯鹿（Rangifer tarandus platyrhynchus）的第一颗（m1）和第二颗（m2）下颌恒磨牙嵌入聚甲基丙烯酸甲酯（PMMA）中，制备切割和抛光表面，并涂上蒸发碳，然后在扫描电子显微镜（BSE-SEM）中使用20 kV背散射电子成像技术，研究在微米和亚微米尺度上依赖于矿化程度的牙齿组织结构方面。BSE-SEM揭示了继发性牙骨质与原发性和继发性牙本质中生长层（环纹）矿物质含量的差异，顺便说一下，m1在死亡时仍在形成后者。在活跃的沉积阶段，牙骨质中形成了矿化程度较低的宽条带组织。当冬季生长减缓时，现有组织通过成熟矿化形成薄而致密的条带。这种成熟过程类似于板层骨和关节软骨中所见的过程。与之前的观点相反，有证据表明继发性牙骨质在整个生命过程中存在大量吸收和修复以及牙本质的形成。继发性牙本质像牙骨质一样按矿物质含量分层。在牙冠中，这主要是具有明显球间牙本质层的管状牙本质。在牙髓腔下部和牙根中，它基本上没有小管。在m2根尖区域的牙骨质-牙本质交界处发现的大量非矿化空间代表了两种组织之间赫特维希上皮根鞘（HERS）或马拉瑟上皮剩余（ERM）的包含物，这种现象以前仅在鼠科动物中被识别。驯鹿牙齿组织中导致增量线（环纹）形成的解剖学变化，首次在微米水平上被识别，可能在大多数（如果不是全部）生活在季节性环境中的长寿哺乳动物物种中普遍存在。
