Raman studies on amino acids profiles at the dentin-enamel-junction in human and ancient/recent animal teeth

Raman microscopy enables the delimitation of the dentin-enamel junction (DEJ) in human and animal teeth, by using, e.g., the 1 oscillations of PO43- (960 cm-1) for the boundary with the enamel and of stretching modes for C-H2 (~2935 cm-1) for the boundary with the dentin and it can be strictly compared with the optical image of DEJ. In this way, one can observe the distribution of some elements of collagen fibrils crossing DEJ, by using the oscillations for proline ( (C-C) of ring at 855 and 921 cm-1), for hydroxyproline ( (C-C) of ring at 876 cm-1), and for phenylalanine ( (C-C) of ring ~1003 cm-1). The systematic although not identical drop in the concentrations of these amino acids was observed on passing from the dentin to enamel side. Several other oscillations were traced as well (for organic chain fragments, amide groups). The observation was widened on the zones adhering on the enamel side (up to 15 m) and on the dentin side (15 m outside the boundary) to the DEJ. The investigations suggest the reorganization of the organic matter in these zones.