Identification of chemical transformations in enamel apatite during the development of fissure caries at the nanoscale by means of synchrotron infrared nanospectroscopy: A pilot study

Abstract

The spectral data sets obtained in our work using classical micro Fourier transform infrared spectroscopy (μFTIR) and modern broadband synchrotron infrared nanospectroscopy (SINS) methods, as well as their analysis and comparison with the known μFTIR spectroscopic results, provide new fundamental information on the mechanisms of pathological processes development in the carious fissure region of a human tooth at the level of enamel apatite crystallites (nano level). The infrared vibration signatures detected in our nanoscale study allowed us to establish gradient changes in chemical composition (phase transformations) occurring within the enamel roads at the level of apatite nanocrystals forming a prism, also to estimate changes in the crystallinity coefficient and the proportion of acid phosphates, as well as the depth of bacteria metabolism products (acid invasion). The results of the comparative study of this technique demonstrate that the combination of s-SNOM, IR spectroscopy and synchrotron broadband source in the SINS method provides excellent chemical sensitivity, sufficient for the providing of chemical identification of phase transformations with enhanced spatial resolution of ∼25 nm and the depth of useful signal output of several tens of nanometers. These advantages of SINS claim to be an advanced approach for investigations of objects of biological nature at a qualitatively new level.