We are developing new optics-based methods for the detection and longitudinal monitoring of incipient caries based on combining imaging from optical coherence tomography (OCT) and biochemical specificity from polarized Raman spectroscopy (PRS). OBJECTIVES: To use OCT and PRS to distinguish sound enamel from incipient caries on extracted human teeth. METHODS: Using a sampling of extracted teeth, OCT imaging at 850 nm and PRS measurements at 830 nm were independently obtained ex vivo. From sound and carious regions, the mean optical attenuation coefficient (μ_t) was calculated from compounded A-scans of the OCT images. Similarly, the mean Raman depolarization ratio (ρ) of the main hydroxyapatite peak at 959 cm^-1 was determined. RESULTS: The results of the 95% confidence intervals of the μ_t and ρ parameters for sound and carious enamel are shown. In parentheses are the number (n) of tooth samples and measurement points, respectively.

	95% Confidence Intervals
Parameter	Sound Enamel	Incipient Caries
mean μt (mm-1)	1.32-1.38 (n=21, n=336)	0.77-0.95 (n=13, n=165)
mean ρ	0.155-0.187 (n=15, n=106)	0.405-0.513 (n=10, n=50)

CONCLUSIONS: OCT light signal rapidly decays in sound enamel being strongly attenuated when compared to the signal from porous carious regions characterized by deeper light penetration. The depolarization ratio is higher for incipient caries than for sound enamel due to demineralization induced changes in mineral structure and crystal orientation. Differences between sound enamel and incipient caries in both μ_t and ρ are statistically significant at p<0.05. Therefore OCT and PRS offer potential for reliably discriminating sound enamel from incipient lesions non-destructively. Funded by the Canadian Institutes of Health Research.

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