Multispectral cross-polarization reflectance measurements suggest high contrast of demineralization on tooth surfaces at wavelengths beyond 1300nm due to reduced light scattering in sound enamel.

Abstract

The enamel scattering coefficient decreases markedly with increasing wavelength from the visible to the near-infrared (NIR). However, beyond 1300nm, the scattering coefficient is difficult to measure, and it is not known whether light scattering continues to decrease significantly at longer wavelengths. It is hypothesized that water absorption is a major contributor to the contrast between sound and demineralized enamel beyond 1300nm since deeply penetrating photons in sound enamel are likely absorbed by water. Reflectance images of demineralization on tooth surfaces were acquired at wavelengths near 1450, 1860, 1880, and 1950nm. The magnitude of water absorption is similar at 1450 and 1880nm but varies markedly between 1860, 1880, and 1950nm. Multispectral comparisons of lesion contrast provide insight into the mechanism responsible for higher contrast at longer NIR wavelengths. The highest contrast was at 1950nm; however, the markedly higher contrast at 1880 compared to 1450nm and similar contrast between 1860 and 1880nm suggests that the enamel scattering coefficient continues to decrease beyond 1300nm, and that reduced light scattering in sound enamel is most responsible for the higher lesion contrast at longer NIR wavelengths. This has important implications for the choice of wavelengths for caries detection and diagnostic devices, including the performance of optical coherence tomography beyond 1300nm.