Enamel thickness variation of deciduous first and second upper molars in modern humans and Neanderthals

Enamel thickness and dental tissue proportions have been recognized as effective taxonomic discriminators between Neanderthal and modern humans teeth. However, most of the research on this topic focused on permanent teeth, and little information is available for the deciduous dentition. Moreover, although worn teeth are more frequently found than unworn teeth, published data for worn teeth are scarce and methods for the assessment of their enamel thickness need to be developed. Here, we addressed this issue by studying the 2D average enamel thickness (AET) and 2D relative enamel thickness (RET) of Neanderthal and modern humans unworn to moderately worn upper first deciduous molars (dm1s) and upper second deciduous molars (dm2s). In particular, we used 3D μCT data to investigate the mesial section for dm1s and both mesial and buccal sections for dm2s. Our results confirmed previous findings of an Neanderthal derived condition of thin enamel, and thinner enamel in dm1s than dm2s in both Neanderthal and modern humans. We demonstrated that the Neanderthal 2D RET indices are significantly lower than those of modern humans at similar wear stages in both dm1s and dm2s (p < 0.05). The discriminant analysis showed that using 2D RET from dm1 and dm2 sections at different wear stages up to 93% of the individuals are correctly classified. Moreover, we showed that the dm2 buccal sections, although non-conventionally used, might have an advantage on mesial sections since they distinguish as well as mesial sections but tend to be less worn. Therefore, the 2D analysis of enamel thickness is suggested as a means for taxonomic discrimination between modern humans and Neanderthal unworn to moderately worn upper deciduous molars.