The Distribution and Biogenic Origins of Zinc in the Mineralised Tooth Tissues of Modern and Fossil Hominoids: Implications for Life History, Diet and Taphonomy

Simple Summary Teeth begin to grow in the jaws before birth and continue to appear in an overlapping sequence until each is complete in length. Subsequently, the central pulp (nerve) chamber of each tooth slowly fills in with dentine and the root of the tooth continues to accumulate thin layers of cementum until the individual dies. Each of the tooth tissues, the hard enamel cap, the dentine core of the tooth and the root cementum grow incrementally and incorporate small quantities of blood-born trace elements ingested from our diet into their structure. A chronological record of zinc incorporation exists in each tooth tissue and can be visualised in thin sections, or slices, of teeth using a beam of synchrotron light. Zinc markings in teeth are especially useful and occur at birth in enamel and dentine and annually in the cementum layers. This work shows that zinc is consistently concentrated within surface enamel and in the dentine surrounding the central pulp chamber. Knowing where to sample Zn in modern and fossil teeth enables us to reconstruct a chronology of growth and to determine something about diet in the past from the remnants of different Zn isotopes contained in different foodstuffs.Abstract Zinc is incorporated into enamel, dentine and cementum during tooth growth. This work aimed to distinguish between the processes underlying Zn incorporation and Zn distribution. These include different mineralisation processes, the physiological events around birth, Zn ingestion with diet, exposure to the oral environment during life and diagenetic changes to fossil teeth post-mortem. Synchrotron X-ray Fluorescence (SXRF) was used to map zinc distribution across longitudinal polished ground sections of both deciduous and permanent modern human, great ape and fossil hominoid teeth. Higher resolution fluorescence intensity maps were used to image Zn in surface enamel, secondary dentine and cementum, and at the neonatal line (NNL) and enamel-dentine-junction (EDJ) in deciduous teeth. Secondary dentine was consistently Zn-rich, but the highest concentrations of Zn (range 197-1743 ppm) were found in cuspal, mid-lateral and cervical surface enamel and were similar in unerupted teeth never exposed to the oral environment. Zinc was identified at the NNL and EDJ in both modern and fossil deciduous teeth. In fossil specimens, diagenetic changes were identified in various trace element distributions but only demineralisation appeared to markedly alter Zn distribution. Zinc appears to be tenacious and stable in fossil tooth tissues, especially in enamel, over millions of years.