Investigating the Effects of Enamel Growth Variables on Linear Enamel Hypoplasia in Primates

线性釉质发育不全（莱赫）是一种牙釉质缺陷，反映了生命早期牙齿形成时所经历的营养或疾病压力。当这种生理应力破坏正常的釉质生长时，这些缺陷形成，导致在釉质表面上形成线性格罗夫斯。在灭绝的和现存的灵长类物种中，它们表现出这些釉质缺陷的频率存在一致的差异。在类人猿中，倭黑猩猩的莱赫频率最高。黑猩猩和猩猩比大猩猩表现出更高的频率，而低地大猩猩比山地大猩猩表现出更高的频率。在人类祖先中，南方古猿的多重缺陷频率高于傍人，尼安德特人的莱赫频率高于一些现代人类群体，但不是其他人。研究人员通常认为，这些莱赫频率的差异物种之间的压力经验的差异是一个直接的反映。然而，不同的物种也有不同的方式，他们的牙釉质生长。这是很有可能的，物种特异性差异方面的釉质生长影响的模式，已观察到的分布莱赫在灵长类动物。最近对现代人类的研究表明，牙釉质生长的各个方面影响牙齿记录生理压力的方式。具体而言，由叠瓦状釉质（釉质被perikymata覆盖，称为Retzius纹的内部生长增量的外部表现）组成的牙冠的百分比影响缺陷形成的机会，而perikymata的深度影响缺陷的可感知性。这项研究代表了第一次系统的调查，在何种程度上这些釉质生长变量可以解释灵长类动物物种之间的莱赫患病率的差异。这项研究的智力价值在于它将提供对牙釉质结构如何约束跨物种缺陷形成的洞察。通过了解这些限制，更清楚地解释线性釉质发育不全揭示了化石和活的灵长类动物，包括人类的生理压力，将是可能的。要回答的问题，如何釉质生长变量影响莱赫患病率跨物种，本研究探讨了内部（条纹Retzius）和外部（perikymata）釉质生长结构在70个灵长类动物物种。更广泛的影响包括创建一个大型复制品样本的灵长类动物牙齿标本选择保存其表面上的perikymata。因为perikymata提供了釉质生长的记录，它们可以用于灵长类动物生长和发育的其他研究。该样本将成为俄亥俄州州立大学生物考古学实验室收藏的Menegaz-Bock牙模的一部分，并将提供给其他研究人员。因此，该项目将对体质人类学研究的基础设施产生积极影响。PI在研究生和本科生的实验室练习中使用了以前研究的原始数据;从这项研究中产生的数据也将以这种方式使用。最后，牙科人类学是一个传统上女性科学家代表性不足的领域。该项目的博士后合作者是一位女科学家，该项目将支持她的专业发展。

Linear enamel hypoplasia (LEH) is a defect of tooth enamel that reflects periods of nutritional or disease stress experienced during the early years of life, when teeth are forming. These defects form when such physiological stresses disrupt normal enamel growth, causing the formation of linear groves on the enamel surface. There are consistent differences among both extinct and living primate species in the frequency with which they exhibit these enamel defects. Of the great apes, bonobos have the highest frequencies of LEH. Chimpanzees and orangutans exhibit higher frequencies than gorillas, and lowland gorillas exhibit higher frequencies than mountain gorillas. Among human ancestors, Australopithecus has higher frequencies of multiple defects than Paranthropus, and Neanderthals exhibit LEH frequencies higher than some modern human groups but not others. Researchers usually assume that these LEH frequency differences among species are a direct reflection of differences in stress experience. However, species also differ in the way that their enamel grows. It is highly likely that species-specific differences in aspects of enamel growth are influencing the patterns that have been observed in the distribution of LEH in primates. Recent studies in modern humans have demonstrated that aspects of enamel growth affect how teeth record physiological stresses. Specifically, the percentage of the tooth crown composed of imbricational enamel (enamel covered by perikymata, external manifestations of internal growth increments known as striae of Retzius) affects the opportunity for defects to form, while the depth of perikymata affects defect perceptibility. This study represents the first systematic investigation of the extent to which these enamel growth variables can account for differences in LEH prevalence across primate species. The intellectual merit of this study lies in the insight it will provide into how the structure of enamel constrains defect formation across species. By understanding these constraints, clearer interpretations of what linear enamel hypoplasias reveal about physiological stress in fossil and living primates, including humans, will be possible. To answer the question of how enamel growth variables affect LEH prevalence across species, this study examines both internal (striae of Retzius) and external (perikymata) enamel growth structures across 70 primates species. Broader impacts include the creation of a large replica sample of primate dental specimens selected for the preservation of perikymata on their surfaces. Because perikymata provide a record of enamel growth, they can be used in additional studies of primate growth and development. This sample will be become part of the Menegaz-Bock dental cast collection housed in the Bioarchaeology Laboratory at The Ohio State University and will be made available to other researchers. Thus, this project will have a positive impact on the infrastructure of research in physical anthropology. The PI has used raw data from previous research in lab exercises in both graduate and undergraduate classes; data generated from this research will be used in this way as well. Finally, dental anthropology is a field in which female scientists have been traditionally underrepresented. The post-doctoral collaborator on this project is a female scientist, and this project will support her professional development.