Description
Deep ultraviolet (DUV) Raman spectroscopy was employed to probe molecular and structural alterations in human enamel following orthophosphoric acid etching, used here as an in vitro model of hydroxyapatite loss and surface conditioning. Benefiting from resonance enhancement and intrinsic fluorescence suppression, the technique enabled the direct acquisition of high-quality spectra from intact tooth surfaces without sample preparation. Spectral analysis revealed a systematic decrease in the phosphate ν₁ band (~950 cm⁻¹), accompanied by a relative increase in the protein-associated amide I band (~1620 cm⁻¹) in treated regions. This resulted in a marked reduction of the mineral-to-organic ratio (I₉₅₀/I₁₆₂₀), reflecting localized demineralization of hydroxyapatite and increased exposure of the organic matrix. To address intra-sample heterogeneity and improve sensitivity to localized changes, a within-tooth comparative approach was adopted. In addition, Partial Least Squares Discriminant Analysis (PLS-DA) was applied as a chemometric tool to identify the most discriminative spectral features and inform the selection of robust band ratios. This approach establishes a foundation for future validation of predictive models. Overall, these findings demonstrate that DUV Raman spectroscopy is a sensitive, non-destructive, and label-free technique for detecting early-stage enamel demineralization, with promising applications in dental diagnostics and the evaluation of restorative treatments.
