Exploring metameric variation in human molars: a morphological study using morphometric mapping
Exploring metameric variation in human molars: a morphological study using morphometric mapping
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探索人类臼齿的同色异谱变异：使用形态测量映射的形态学研究
作者：
Morita W;Morimoto N;Ohshima H
人类臼齿表现出一种类型的同色异谱变异，这是生物体内连续重复形态的差异。已经提出了各种理论来解释这种变化是如何在臼齿中产生的。然而，由于方法上的限制，支持这些理论的现实数据仍然相对稀少。在这里，我们提出了新的方法来分析详细的牙冠形态。我们应用形态测量映射到人类上颌磨牙的牙釉质牙本质交界处，并检查牙发生模型是否适用于人类上颌磨牙。我们的研究结果表明，上颌第一磨牙是表型不同的上颌磨牙。上颌第一磨牙的平均形状特征是四个轮廓分明的尖突和咬合面陡峭的表面起伏。而上颌第三磨牙的特点是咬合面起伏平滑，形态变异较大，形态空间分布规律明显。上第二磨牙代表第一和第三磨牙之间的中间状态。通过异速生长向量分析研究了与尺寸相关的形状变化，并且随着尺寸的增加，人类上颌磨牙倾向于向上颌第一磨牙的形状收敛。因此，上颌第一磨牙与上颌第二磨牙和第三磨牙之间的差异在很大程度上可以解释为异速生长效应。总的来说，这些结果表明，观察到的人类磨牙的同色异谱变异模式与磨牙列结构（抑制级联模型）和磨牙冠形态（图案级联模型）的牙发生模型一致。这项研究表明，形态测量映射是一个有用的工具，可视化和量化牙齿的形态特征，这可以提供更好地了解牙齿的演变连接形态和发展的基础。
Human molars exhibit a type of metameric variation, which is the difference in serially repeated morphology within an organism. Various theories have been proposed to explain how this variation is brought about in the molars. Actualistic data that support the theories, however, are still relatively scarce because of methodological limitations. Here we propose new methods to analyse detailed tooth crown morphologies. We applied morphometric mapping to the enamel–dentine junction of human maxillary molars and examined whether odontogenetic models were adaptable to human maxillary molars. Our results showed that the upper first molar is phenotypically distinct among the maxillary molars. The average shape of the upper first molar is characterized by four well‐defined cusps and precipitous surface relief of the occlusal table. On the other hand, upper third molar is characterized by smooth surface relief of the occlusal table and shows greater shape variation and distinct distribution patterns in morphospace. The upper second molar represents an intermediate state between first and third molar. Size‐related shape variation was investigated by the allometric vector analysis, and it appeared that human maxillary molars tend to converge toward the shape of the upper first molar as the size increases. Differences between the upper first molar and the upper second and third molar can thus be largely explained as an effect of allometry. Collectively, these results indicate that the observed pattern of metameric variation in human molars is consistent with odontogenetic models of molar row structure (inhibitory cascade model) and molar crown morphology (patterning cascade model). This study shows that morphometric mapping is a useful tool to visualize and quantify the morphological features of teeth, which can provide the basis for a better understanding of tooth evolution linking morphology and development.