Abstract
We report the utility of a rapid polarization-resolved hyperspectral stimulated Raman scattering (SRS) imaging technique developed for optical diagnosis and characterization of dental caries in the tooth. Hyperspectral SRS images (512 × 512 pixels) of the tooth covering both the fingerprint (800-1800 cm(-1)) and high-wavenumber (2800-3600 cm(-1)) regions can be acquired within 15 minutes, which is at least 10(3) faster in imaging speed than confocal Raman mapping. Hyperspectral SRS imaging uncovers the biochemical distributions and variations across the carious enamel in the tooth. SRS imaging shows that compared to the sound enamel, the mineral content in the body of lesion decreases by 55%; while increasing up to 110% in the surface zone, indicating the formation of a hyper-mineralized layer due to the remineralization process. Further polarized SRS imaging shows that the depolarization ratios of hydroxyapatite crystals (ν 1-PO4 (3-) of SRS at 959 cm(-1)) of the tooth in the sound enamel, translucent zone, body of lesion and the surface zone are 0.035 ± 0.01, 0.052 ± 0.02, 0.314 ± 0.1, 0.038 ± 0.02, respectively, providing a new diagnostic criterion for discriminating carious lesions from sound enamel in the teeth. This work demonstrates for the first time that the polarization-resolved hyperspectral SRS imaging technique can be used for quantitatively determining tooth mineralization levels and discriminating carious lesions from sound enamel in a rapid fashion, proving its promising potential of early detection and diagnosis of dental caries without labeling.
Highlights
Dental caries is caused by an imbalance between the demineralization and re-mineralization processes of the tooth related to the acid generated from the bacterial activity [1]
Unlike stimulated Raman scattering (SRS) signal at 959 cm−1, SRS signal at 1070 cm−1 in the surface zone does not increase to a level higher than the sound enamel due to the loss of carbonate in the demineralization process and the reduced carbonate uptake during the remineralization process [24]
Stronger THG signals are observed in the body of lesion and translucent zone compared to the sound enamel and surface zone in the tooth [Fig. 2(e)], indicating the increase of the optical heterogeneity inside the enamel rods in the body of lesion and translucent zone due to the carious process
Summary
Dental caries is caused by an imbalance between the demineralization and re-mineralization processes of the tooth related to the acid generated from the bacterial activity [1]. Diagnostic techniques, such as fiber optic trans-illumination [4], quantitative light-induced fluorescence [5], have problem with high false positive or false negative rates for detecting early stage of dental caries. Due to the extremely weak tissue Raman scattering process, the measurements of tissue micro-Raman images may take tens of hours, hampering its wide applications in rapid diagnosis and characterization of biomedical tissues. The concomitant strong fluorescence background from tooth samples may overwhelm weak tissue Raman signals [9], making micro-Raman imaging on dental caries even more challenging. We report the utility of a rapid polarization-resolved hyperspectral SRS imaging technique developed for optical diagnosis and characterization of carious lesions in the tooth without labeling. The complementary information acquired in both the FP and HW Raman regions can further improve the understanding of biochemical/biomolecular distributions and orientations associated with carious lesions in the tooth
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