Abstract: Optical imaging in medical field is crucial for early detection of oral diseases, to carry out more effective minimally-invasive targeted-therapies and to restore diseased tissues functionally and aesthetically. Optical methods can be based on the properties of light scattering, absorption and fluorescence. In doing so, LEDs and classical light sources can be used. All of these methods have one basic principle in common; the optical spectrum of a tissue contains information about the biochemical composition and/or the structure of the tissue, which provide diagnostic information for tissue characterization. Among them, the most promising techniques to detect and classify different stages of caries are those based on the quantitative measurements of tooth auto fluorescence and diffuse reflectance.