High Contrast Reflectance Imaging of Simulated Lesions on Tooth Occlusal Surfaces at Near-IR Wavelengths

IntroductionIn vivo and in vitro studies have shown that high contrast images of tooth demineralization can be acquired in the near-infrared (near-IR) without the interference of stain. The purpose of this study is to compare the lesion contrast in reflectance at near-IR wavelengths coincident with high water absorption with those in the visible, the near-IR at 1,300nm and with fluorescence measurements for early lesions in occlusal surfaces. MethodsTwenty-four human molars were used in this in vitro study. Teeth were painted with an acid-resistant varnish, leaving a 4x4mm window in the occlusal surface of each tooth exposed for demineralization. Artificial lesions were produced in the exposed windows after 1- and 2-day exposure to a demineralizing solution at pH 4.5. Lesions were imaged using near-IR reflectance at three wavelengths, 1,300, 1,460, and 1,600nm using a high definition InGaAs camera. Visible light reflectance, and fluorescence with 405nm excitation and detection at wavelengths greater than 500nm were also used to acquire images for comparison. Crossed polarizers were used for reflectance measurements to reduce interference from specular reflectance. ResultsThe contrast of both the 1- and 2-day lesions were significantly higher (P<0.05) for near-IR reflectance imaging at 1,460 and 1,600nm than it was for near-IR reflectance imaging at 1,300nm, visible reflectance imaging, and fluorescence. ConclusionThe markedly higher contrast at 1,460 and 1,600nm wavelengths, coincident with higher water absorption, suggest that these wavelengths are better suited than 1,300nm for imaging early/shallow demineralization on tooth surfaces. Lasers Surg. Med. 45:533-541, 2013. (c) 2013 Wiley Periodicals, Inc.