Caries (commonly called cavities) in teeth can be seen more easily under near-IR (NIR) light than visible light, and in fact show higher contrast in NIR than under the blue light used for quantitative light fluorescence (a dentist’s visualization technique that causes teeth to fluoresce green, showing caries as dark spots). Researchers at the University of California–San Francisco, undertook to find the best NIR wavelengths between 1200 and 1600 nm for spotting caries in teeth. They found that 1460 nm, a wavelength that has high water absorption, is best for reflectance imaging, while 1300 nm was better for off-angle illumination.
Teeth extracted from San Francisco area residents were cleaned, sterilized, and viewed with x-rays to allow selection of teeth with small, hard-to-find caries. In addition, some caries-free teeth were sliced apart and drilled, and the resulting holes filled with a substance imitating caries. A halogen fiber-optic illuminator with a series of bandpass filters provided the light, while a visible/NIR camera with response from 400 to 1600 nm captured the images. Three different setups allowed normal-incidence reflectance, side illumination, and transmission imaging. Well-hydrated teeth worked best for side illumination and transmission, while air-dried teeth were best imaged under reflection.
Contact Cynthia Darling at [email protected].
