Previous studies have shown that near-infrared (NIR) reflectance and transillumination imaging can be used to acquire high contrast images of early caries lesions and composite restorative materials. The aim of the study was to determine the optimum NIR wavelengths for imaging demineralized areas under dental sealants. Fifteen natural human premolars and molars with occlusal lesions were used in this in vitro study. Images before and after application of sealants were acquired using NIR reflectance and NIR transillumination at wavelengths of 1300, 1460, and 1500 to 1700 nm. Images were also acquired using polarization sensitive optical coherence tomography (OCT) for comparison. The highest contrast for NIR reflectance was at 1460 nm and 1500 to 1700 nm. These NIR wavelengths are coincident with higher water absorption. The clear Delton sealant investigated was not visible in either copolarization or cross-polarization OCT images. The wavelength region between 1500 and 1700 nm yielded the highest contrast of lesions under sealants for NIR reflectance measurements.