XRD and FTIR crystallinity indices in sound human tooth enamel and synthetic hydroxyapatite

The crystallinity index (Cl) is a measure of the percentage of crystalline material in a given sample and it is also correlated to the degree of order within the crystals. In the literature two ways are reported to measure the Cl: X-ray diffraction and infrared spectroscopy. Although the Cl determined by these techniques has been adopted in the field of archeology as a structural order measure in the bone with the idea that it can help e.g. in the sequencing of the bones in chronological and/or stratigraphic order, some debate remains about the reliability of the Cl values. To investigate similarities and differences between the two techniques, the Cl of sound human tooth enamel and synthetic hydroxyapatite (HAP) was measured in this work by X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR), at room temperature and after heat treatment. Although the (CI)(XRD) index is related to the crystal structure of the samples and the (CI)(FTIR) index is related to the vibration modes of the molecular bonds, both indices showed similar qualitative behavior for heat-treated samples. At room temperature, the (CI)(XRD) value indicated that enamel is more crystalline than synthetic HAP, while (CI)(FTIR) indicated the opposite. Scanning (SEM) and transmission (TEM) images were also used to corroborate the measured Cl values. (C) 2013 Elsevier B.V. All rights reserved.