上世纪70年代在许家窑-侯家窑地点发现的人类化石对了解东亚中晚更新世过渡时期古人类的形态演化起到了重要作用。除形态特征外,针对许家窑人病理表现也开展过相关研究,其中许家窑人幼年个体前部牙齿上出现的黄色小坑被认为是患有氟斑牙病的证据,且可能代表世界范围内该牙病的最早实例。然而,经电子显微镜和显微断层扫描显示,这些黄色小坑或凹陷是釉质发育不良表现,而不是代表个体患有氟斑牙病后牙齿受咀嚼压力而产生的物理破损。同步辐射扫描显示,许家窑幼年个体前部牙齿釉质密度均匀,没有出现浅层釉质矿化减小的现象,不支持该个体因釉质矿化过程受影响而患有典型氟斑牙的结论。尽管如此,后部牙齿上大量坑状的釉质缺陷和坑状缺陷底部的加重生长线特征不排除是个体氟摄入过量而影响釉质形成的分泌期而导致的。除表面坑状釉质缺陷外,许家窑幼年个体恒齿不同部位的釉质内部出现缺失（空间结构一般为圆球状）。缺失主要集中在浅层区域,沿齿尖-齿颈方向的密集程度变化与釉质发育不良位置具有一定相关性。釉质内部缺失有时互连并与釉质表面垂直。以上特征显示釉质内部缺失是釉质形成过程受影响所致,且影响因素和发生机理可能与釉质发育不良的类似。许家窑幼年个体不同牙齿在外部釉质缺陷和内部釉质缺失密集程度上的差别可能反映的是个体在发育过程中所需应对的外界扰动因素程度不同。未来研究可对包含许家窑人化石的堆积物中以及许家窑人牙齿中的氟含量进行测定,以进一步研究许家窑人个体的生活环境中是否有过量的氟以及许家窑人是否摄入了过量氟元素,从而对许家窑人的牙齿发育缺陷机理有一个进一步的了解。

The hominin fossils recovered from Xujiayao-Hsuchiayao (Locality 74093）site is critical in understanding the morphological variability of hominins from the period of Middle to late Pleistocene transition. Other than the morphologies, the pathological aspects of Xujiayao hominins were also investigated and the juvenile (Xujiayao 1) was believed to be suffered from dental fluorosis based on the presence of the yellow pit or furrow on its anterior teeth. The incidence of “dental fluorosis” in Xujiayao has been thought to represent the earliest evidence of this pathological anomaly. However, with the use of scanning electron microscopy (SEM) and microcomputed tomography (micro-CT), the yellow enamel defects were found to be hypoplastic alternation that occurred before the tooth eruption. They were not post-eruptive physical breakage resulted from chewing force and therefore don’t support the diagnosis of dental fluorosis. In addition, synchrotron phase-contrast microtomography of the anterior teeth under both micron and submicron resolutions didn’t show obvious sign of subsurface hypomineralization along the sagittal section of the enamel, and it doesn’t support the occurrence of dental fluorosis resulted from the disturbance of enamel maturation phase. However, plenty of pit-type hypoplastic defects were present on the enamel surface of the Xujiayao permanent teeth and the bottom of the enamel pits were underlain by accentuated incremental line. This type of enamel defects could be resulted from distributed secretory stage of enamel formation by excessive fluoride intake according to the experimental study on mammals. Apart from the surface defects, synchrotron scanning under submicron resolution at four different spots of Xujiayao permanent teeth reveals plenty of enamel holes inside the crown. These holes have a sphere-like shape and generally restricted to outer one-third area of the enamel thickness. Different locations within one scanning spot vary in the density of enamel holes. In canine, the enamel holes of high-density correspond with a hypoplastic depression on the enamel surface. Enamel holes inside the paracone apex of m¹ are in some cases connected with each other, with the main axis perpendicular to the outer enamel surface. These characteristics indicate a non-random distribution pattern of the enamel holes, and that they might be caused by the same effects as that of enamel hypoplasia. Teeth forming at different times vary in the density of hypoplastic pits and enamel holes, and this might imply various level of physiological disturbance at different stages of dental growth and development. Future study could further quantify the fluoride content in the deposit containing the Xujiayao hominin fossils, as well as in the tooth enamel, in order to ascertain if the Xujiayao people used to live a fluoride-rich environment and if they did ingest enough fluoride. With this information, the mechanism of enamel defects in Xujiayao juvenile could be more thoroughly understood.