The development of new diagnostic technologies based on the light scattering and autofluorescence properties of den- tal tissues is required to improve the diagnostic ability of ini- tial caries lesions earlier than previously done and promot- ing the potential of treatment without surgical intervention. The aim of this study is to correlate fluorescence-based re- sults provided by multiphoton microscopy (MPM) with con- focal Raman microscopy records using phosphate level at 960 cm–1 and the organic matrix at ∼2,931 cm–1 in healthy and demineralized human enamel. Measurements on 14 teeth were made using two incident lights of different wave- lengths, released by confocal Raman microscopy and MPM. Raman phosphate peak intensity at 960 cm–1 along with or- ganic to mineral ratio at (2,931/430 cm–1) and nonlinear opti- cal signals (second harmonic generation [SHG] and intrinsic two-photon excited fluorescence [I2PEF]) were recorded from the demineralized and healthy enamel sites. Raman spectral maps showed that the higher the organic/mineral ratio in the demineralized enamel, the lower the intensity of mineral component in the same zone. MPM revealed new optical indicators of carious lesion as shown by the presence of a red-shifted fluorescence peak in the 650- to 750-nm area of the fluorescence spectrum of demineralized enamel. Moreover, on sample regions with insignificant autofluores- cence, the emergence of the SHG signal could be noted. By comparing I2PEF images with the structural motifs observed by the confocal Raman imaging system, the morphological similarity of the acquired images was quite evident. Any change in the I2PEF spectra reflects alterations in the chem- ical composition of enamel. These findings may provide an important basis for potentially valuable applications of pho- tonic tools in the clinical diagnosis of tooth pathological con- ditions, besides exposing the fundamental role of organic matrix in enamel integrity and reparation.

Nitrogen-vacancy centers in diamonds possess an electronic spin resonance that strongly depends on temperature, which makes them efficient temperature sensors with sensitivity down to a few mK/√Hz. However, the high thermal conductivity of the host diamond may strongly damp any temperature variations, leading to invasive measurements when probing local temperature distributions. In the view of determining possible and optimal con gurations for diamond-based wide- eld thermal imaging, here, we investigate both experimentally and numeri- cally the effect of the presence of diamonds on microscale temperature distributions. Three geometrical con gurations are studied: a bulk diamond substrate, a thin diamond layer bonded on quartz, and diamond nanoparticles dispersed on quartz. We show that the use of bulk diamond substrates for thermal imaging is highly invasive in the sense that it prevents any substantial temperature increase. Conversely, thin diamond layers partly solve this issue and could provide a possible alternative for microscale thermal imaging. Dispersions of diamond nanoparticles throughout the sample appear as the most relevant approach as they do not affect the temperature distribution, although NV centers in nanodiamonds yield lower temperature sensitivities than bulk diamonds.