Application of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) for the identification of potential diagenesis and crystallinity changes in teeth

Abstract

During burial, diagenetic alteration can invalidate the paleodietary signature, which the hydroxyapatite (Ca 5(PO 4) 3OH) matrix in incremental tissues, such as tooth enamel, provides. Thus, analytical methods that can evaluate diagenetic changes are crucial in anthropological and archaeological investigations. Modern deciduous tooth enamel (exfoliated) from Solis, Mexico and Kalama, Egypt, as well as Bronze Age (circa 2200 B.C.E.) adult enamel from (present-day) Tell Abraq, U.A.E. and adult enamel from the New York African Burial Ground (NYABG) in lower Manhattan, were analyzed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The samples were compared to synthetic hydroxyapatite powder and bone ash samples. The DRIFTS spectra of tooth enamel yielded similar infra red finger print pattern to previous pellet-based FTIR spectra in both absorbance and Kubelka–Munk units. The study demonstrates that DRIFTS is a convenient alternative to pellet-based transmission FTIR in testing diagenetic changes in hard tissue for archaeological investigations. Tooth enamel samples contained a higher carbonate–phosphate ratio than synthetic hydroxyapatite and bone ash standard samples. Correlations are reported between Crystallinity Index (CI Ab) and carbonate–phosphate ratio, strontium–calcium ratio, and fluoride peak appearance. Crystallinity indexes (CI Ab) were in the range of 2.6–3.8 (in absorbance units) and Kubelka–Munk Crystallinity indexes (CI KM) were in the range of 3.1–4.9.