Optical coherence tomography correlated with a functional fluorescence imaging for detection and quantification of dental caries

Fluorescence radiance loss in enamel following demineralisation has been correlated to the amount of mineral lost during the demineralisation. The correlation between fluorescence loss measured by Quantitative Light-induced Fluorescence (QLF) and the reflectivity loss measured by an en-face Optical Coherence Tomography (OCT) system was investigated in a demineralisation process to produce artificial caries. We used an OCT system which can collect A-scans (reflectivity versus depth graph), B-scans (longitudinal images) and C-scans (en-face images). The power to the sample was 250 μW, wavelength λ = 850 nm and the depth resolution in air 16 μm. Transversal and longitudinal images showed the caries lesion as volumes of reduced reflectivity. A-scans, which show the profile of the reflectivity versus depth of penetration into the tooth tissue, were used for quantitative analysis of the reflectivity loss. Both the fluorescence radiance and reflectivity of the enamel decreased with increasing demineralisation time. A linear correlation was observed between the percentage fluorescence loss measured by QLF and the percentage reflectivity loss measured by OCT. It was concluded that the decrease in reflectivity of the enamel during demineralisation, measured by OCT, could be related to the amount of mineral lost during the demineralisation process.