New insights into non-contact reflectance IR mapping of teeth

Abstract

Teeth are a high mineralized tissue that withstand years of daily usage. Their mechanical properties have been studied at all length scales for decades but only small areas have been the focus of their chemical properties. A comprehensive, spatially resolved examination of the whole system is needed to expand our comprehension of the correlations between the chemistry and the mechanical properties. Specular Reflectance Fourier Transform Infrared Spectroscopy (srFTIR) is a nondestructive technique used to characterize the chemical composition of surfaces by examining the infrared light they reflect. This technique provides high spatial resolution and detailed spectral information, making it useful to study the composition of mineralized tissue. Highly polished dehydrated cross-sectional surfaces of bovine and human teeth were imaged, and spectra were processed using a Kramers-Kronig Transformation to generate absorbance-like data. Results compare well with the well-established FTIR Transmission and Attenuated Total Reflection (ATR) methods. Chemical maps of multiple ν_3-phosphate vibrations, ν_2-carbonate, and amide I, reveal insights into structural and chemical variations across dentine. Young bovine teeth exhibited many chemical and structural similarities to old, partially sclerotic human teeth, affirming their use as proxies in dental research. This work highlights the capability of specular reflection FTIR to preserve spatial information and expand the understanding of tooth microstructure and chemical composition variations.