Micro-CT imaging and analysis of enamel defects on the early late Pleistocene Xujiayao Juvenile

Dental pathologies and enamel defects in East Asian hominins have rarely been reported. Here, we systematically document and describe a suite of enamel defects in the Xujiayao juvenile maxilla, an East Asian hominin from the early Late Pleistocene that may represent an unknown hominin lineage. In addition, we determine the chronology of growth disruptions represented by matched linear enamel hypoplasias, evaluate the long-held hypothesis that the large brownish pit on the I1 is evidence of dental fluorosis and assess the utility of micro-computed tomography (micro-CT) techniques in analyzing enamel defects. With the use of binocular microscopy, scanning electron microscopy (SEM) and micro-CT imaging techniques, the Xujiayao teeth were found to exhibit a high number of pit-form defects seldom seen in the fossil record. By matching the timing of linear enamel hyperplasia across multiple teeth, a minimum of five developmental disruptions were identified, indicating that the Xujiayao juvenile experienced several growth disturbances during its short lifespan. Our SEM and micro-CT analyses suggest that the large pit on the I1 is an enamel hypoplasia due to its morphology and pre-eruptive enamel thinning. It is not a post-eruptive fluorotic pit, and there is no evidence of chalkiness or opacity associated with dental fluorosis. The micro-CT technique made it possible to verify the presence of enamel hypoplasia and to more precisely quantify defect dimensions, especially in unerupted teeth and shallow hypoplasias that are difficult to detect by binocular microscopy or SEM