Synchrotron X-ray fluorescence mapping of Ca, Sr and Zn at the neonatal line in human deciduous teeth reflects changing perinatal physiology

Objectives: Our first objective was to review the evidence describing the appearance and microstructure of theneonatal line in human deciduous teeth and to link this with known changes in neonatal physiology occurring atand around birth. A second objective was to explore ways to improve identification of the neonatal line bymapping the pre- and postnatal distribution of Ca, Sr and Zn in deciduous cuspal enamel and superimposingthese maps onto transmitted light micrographs that included a clear true section of the neonatal line.Materials and methods: We used synchrotron X-ray fluorescence to map elemental distributions in pre- andpostnatal enamel and dentine. Two deciduous canines and 5 deciduous molars were scanned with an X-ray beammonochromatised to 17.0 keV at either 10.0, 2.5 or 1.0 μm resolution and 10 ms integration time.Results: Calcium maps distinguished enamel and dentine but did not clearly demarcate tissues formed pre- orpostnatally. Strontium maps reflected presumed pre- and postnatal maternal serum levels and what are likely tobe diet-dependent regions of Sr enrichment or depletion. Prenatal Zn maps, particularly for dentine, mirrorelevated levels in the fetus and in colostrum during the first few days of life.Conclusions: The neonatal line, enamel dentine junction and surface enamel were all Zn-rich. Within the neonatalline Zn may be associated with increased crystallinity but also with caries resistance, both of which havebeen reported previously. Elemental mapping may improve the identification of ambiguous NNLs and so beuseful in forensic and archaeological studies