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

线性釉质发育不良(LEH)是牙釉质的一种缺陷，反映了在牙齿形成的早期经历的营养或疾病应激时期。当这些生理压力扰乱牙釉质的正常生长，导致牙釉质表面形成线状凹槽时，这些缺陷就会形成。无论是灭绝的灵长类物种还是现存的灵长类物种，在表现这些釉质缺陷的频率上都存在一致的差异。在类人猿中，黑猩猩的LEH频率最高。黑猩猩和猩猩比大猩猩表现出更高的频率，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类人猿，尼安德特人的LEH频率高于一些现代人群体，但不是其他人。研究人员通常认为，不同物种之间LEH频率的差异是压力体验差异的直接反映。然而，不同物种的牙釉质生长方式也不同。在牙釉质生长方面的物种差异很可能正在影响已在灵长类动物中观察到的LEH的分布模式。最近对现代人的研究表明，牙釉质生长的各个方面都会影响牙齿记录生理压力的方式。具体地说，由覆瓦状釉质(釉质被牙周覆盖，内部生长增量的外部表现，称为Retzius条纹)组成的牙冠的百分比会影响缺陷形成的机会，而牙周的深度会影响缺陷的敏感度。这项研究首次系统地研究了这些牙釉质生长变量在多大程度上可以解释不同灵长类动物之间牙釉质肥大患病率的差异。这项研究的学术价值在于它将为牙釉质的结构如何限制跨物种缺陷的形成提供洞察力。通过了解这些限制，可以更清楚地解释线性釉质减少揭示了化石和包括人类在内的现存灵长类动物的生理压力。为了回答釉质生长变量如何影响LEH在不同物种中的患病率的问题，本研究研究了70种灵长类动物的内部(Retzius纹)和外部(周缘)釉质生长结构。更广泛的影响包括创建一个大型灵长类牙齿标本的复制品样本，选择用于保存其表面的周节。由于周缘提供了釉质生长的记录，它们可以用于灵长类生长和发育的进一步研究。这个样本将成为俄亥俄州立大学生物考古实验室收藏的Menegaz-Bock牙科模型的一部分，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练习中使用了以前研究的原始数据；这项研究产生的数据也将以这种方式使用。最后，牙齿人类学是一个传统上女性科学家代表不足的领域。该项目的博士后合作者是一名女性科学家，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.