## 6 RMS Characterization of Dental Lesions
### RMS Characterization of Dental Caries  
Dental caries is one of the most prevalent chronic diseases worldwide, affecting people throughout their lifetime [91]. It is an irreversible microbial disease that affects the calcifiestructures of the tooth. Despite several preventive measures aiming to reduce the incidence of this pathology, such as careful dental hygiene and the addition of fluorine to drinking water, the occurrence of caries is still one of the most common diseases experienced by most individuals [92]. It is known that the organic component can act as an inhibitor of hydroxyapatite crystals' growth during the processes of formation and development of caries, causing organic and inorganic biochemical alterations [68; 93]. Therefore, a detailed analysis of these biochemical changes is mandatory to assess the best approach to help with remineralization of compromised dental tissue [94; 95]. Current clinical diagnostic methods for dental caries detection are based on visual and radiographic examination; hence, they are unable to detect very early-stage lesions [96]. In this light, there is a need to develop new methods able to identify the presence of enamel caries before it is detectable with routine assays. RMS may provide this by characterizing the biochemical composition of healthy and carious enamel and dentine [97]. An in vitro study reported that polarized RMS showed a sensitivity of 97% and a specificity of 100% for the detection of caries [38]. Moreover, another recent study concluded that RMS can be used as a non-contact analytical technology for in vitro studies to discriminate with high resolution the zones of carious dentin tissues by using the amide I/phosphate v1 band ratio, calculated as the ratio between the areas of the bands at 1655 cm\({}^{-1}\) and 960 cm\({}^{-1}\), related to amide I of proteins and v1 of phosphates, respectively [98]. In a previous study, the polarized Raman spectra of enamel, obtained after excitation with the 785 nm laser beam, was used to calculate the depolarization ratio and polarization anisotropy for distinguishing early carious processes. In sound enamel, apatite crystals are ordered in one direction, perpendicular to the enamel surface; in the presence of caries, this ordered arrangement is altered and the structure appears more disordered with enamel crystals that are not parallel to each other. In sound enamel, the depolarization ratio is low and the polarization anisotropy is high; conversely, the first increases and the latter decreases due to disordered carious enamel structure [99]. In the study of [PERSON] et al., the authors highlighted some differences in the intensity, position, and FWHM of the v\({}_{1}\) band of phosphates at 960 cm\({}^{-1}\) between sound and carious enamel. The simultaneous decreases of the value of the band intensity and FWHM were associated with a lower amount of apatite crystals in carious enamel [99]. It is important to check how these band parameters are affected by early demineralization of sound enamel under controlled conditions in order to define RMS as a reliable diagnostic tool in dentistry. [PERSON] et al. observed that the values of the band position increase with enamel demineralization, and this shift to higher wavenumbers was attributed to changes in the vibrational energy of apatite crystals in demineralized enamel. These spectral modifications were also associated with a decrease in the amount of enamel phosphate and a reduction of the order of the structure [99]. [PERSON] et al. reported RMS chemical maps of enamel and dentin caries infiltration [78]. The enamel lesions appeared to be less mineralized due to more substituted carbonate in the crystal lattice compared to the sound enamel. When the lesion extends into the dentin, tissues have less mineral content than the sound dentin; however, many mineral apatites of caries are more crystalline and hence have less substituted carbonate in the lattice.