Trace elements, maturation processes and diagenesis in human deciduous incisors

Post-mortem alteration of trace elements can complicate the interpretation of original biogenic signals related to diet, environment and enamel maturation processes. This study describes gradients in element concentrations for modern and archaeological deciduous incisor teeth to identify diagenetic variations in specific elements. Fifteen human deciduous incisors (six modern and nine archaeological) were prepared for synchrotron radiation micro X-ray fluorescence (SR μ-XRF) analysis targeting the minerals Ca, P, and selected trace elements Zn, Fe, Mn, Cu, and Ba. Standard histological methods were employed to produce thin sections. Element concentrations, expressed in parts per million (ppm) and as a ratio of calcium (Ca), were measured from the outer enamel surface (OES), into the enamel, across the Neonatal Line (NNL) and enamel-dentin junction (EDJ), and into the dentin. Diagenesis was most pronounced on the external surfaces of enamel and dentin, with notable variability in Fe, Mn, Cu, and Ba. In contrast, Ca, P, and Zn levels remained stable across samples, with a slight increase in Zn at the NNL. There was no enrichment of Zn at the OES in enamel not yet matured (less than 33–37 postnatal days), suggesting that initial zinc incorporation is overshadowed by further deposition during maturation. Diagenetic alteration of the Fe, Mn, Cu, and Ba elements in deciduous incisor enamel appears to affect their concentration in regions of the archaeological teeth. The observed Ca and Zn distribution pattern reflects distinct enamel maturation stages, highlighting the need to consider both diagenetic influences and developmental processes in trace element analyses of ancient dental samples.