## 5 Raman Imaging on Sound Hard Dental Tissues  
Besides evaluating the chemical composition of samples by the identification of specific bands, RMS allows one to map specific areas within the analyzed sample by creating false color images, defined as Raman maps, in which the intensities of individual peaks are topographically correlated to the morphology of the mapped area. In this way, it is possible to analyze non-homogeneous samples, such as tissues and cells, in high-resolution to associate chemical composition with morphology [48].  
[PERSON] et al. obtained RMS maps on the vestibular and lingual sides of sound permanent teeth (Figure 3) [48]. The authors concluded that the lowest values of C were displayed by the dentin regions, while homogenous values were found in the enamel of both vestibular and lingual sides. Moreover, an increase in carbonate content was associated with a decrease in C; indeed, dentin showed lower values for C and M/M but had a higher C/P value with respect to enamel.  
Similar results emerged in the study of [PERSON] et al., in which the authors collected Raman maps of the dentin-enamel junction (DEJ) of healthy enamel [70]; they found a transition zone with a thickness of ca. 50 \(\upmu\)m, in which evident variation in terms of mineral and organic components was observed. In general, enamel is characterized by high values of C, due to the presence of well-arranged HA, while dentin is characterized by the lowest values. Furthermore, C slowly decreased from the enamel border to half of the transition  
Figure 3: Raman mapping analysis of representative areas at the inner enamel/dentin interfaces in vestibular and lingual sites of permanent teeth. Photomicrographs reporting the selected areas (red rectangles, 241.5 mm \(\times\) 167 mm) and corresponding false-color images (241.5 mm \(\times\) 167 mm) showing the topographical distribution of mineral/matrix (A960/A1660), crystallinity (inversely proportional to FWHM960), and C/P (carbonates/phosphates, I1070/I960) spectral features. Different color scales (C.S.) were used for a better interpretation of the data: exact values are reported below each map (black/blue color corresponds to the lowest values, green intermediate, and red/dark red to the highest values) [48].  
zone and then dropped down in dentin; the signals related to phosphates followed the same pattern but with a large decrease from the halfway point. An opposite trend was shown by the collagen crosslink signal, which increased considerably from the enamel border to dentin, varying over 10 \(\upmu\)m inside the transition zone. The signals related to the organic component also increased from the enamel border to dentin, reaching the highest value of 10 \(\upmu\)m close to the end of the transition zone [70].  
The mineral composition is not homogeneous within sound enamel tissue; however, more crystallinity (greater mineral crystal size) and greater mineral crystal perfection are observed towards the tooth surface, whereas the mineral apatites are less crystalline and have more carbonate imperfection in the crystal lattice near the enamel-dentin junction [78]. Moreover, enamel has less substituted lattice compared to dentin, indicating the presence of mineral crystals with greater stoichiometric perfection in enamel when compared to dentin [78].