1. A method for quantifying caries, executed at least in part on data processing hardware, the method comprising: generating a digital image of a tooth, the image comprising intensity values for a region of pixels corresponding to the tooth, gum, and background; automatically extracting a lesion area from sound regions of a tooth by identifying tooth regions, extracting suspicious lesion areas, and removing false positives; identifying an adjacent sound region that is adjacent to the extracted lesion area; reconstructing intensity values for tooth tissue within the lesion area according to values in the adjacent sound region; and quantifying the condition of the caries using the reconstructed intensity values and intensity values from the lesion area; wherein identifying tooth regions comprises sub-steps of: generating a first threshold image from a grayscale fluorescence image of the tooth by selecting intensity data values higher than a first predetermined threshold value c 1 ; generating a second threshold image from a grayscale reflectance image of the tooth by selecting intensity data values higher than a second predetermined threshold value c 2 ; generating a preliminary tooth regions image from the intersection of the first and second threshold images; generating a reference binary image from the grayscale fluorescence image by selecting intensity data values higher than a third predetermined threshold value c 3 , wherein threshold value c 3 exceeds threshold value c 1 ; and generating a refined tooth regions image from regions that are in the preliminary tooth regions image and are connected to objects in the reference binary image.