A method for diagnosis and evaluation of tooth decay comprises: locating in an x-ray image the contour of the dento-enamel junction (DEJ) measuring optical density along contours substantially parallel to and on either side of the DEJ contour and calculating at least one numerical decay value from the measured optical densities. A method for diagnosis and evaluation of periodontal disease comprises: measuring in an x-ray image a bone depth (BD) relative to the position of the cemento-enamel junctions (CEJs) of adjacent teeth measuring bone density along a contour between the adjacent teeth and calculating a numerical crestal density (CD) value from the measured bone density. Calibration standards may be employed for facilitating calculation of the numerical values. A dental digital x-ray imaging calibration method for at least partly correcting for variations of the optical densities of images acquired from the dental digital x-ray imaging system.
