To read caries on an x-ray dental film, it is important to learn to differentiate between normal and abnormal tissue, as well as to differentiate between the different meanings indicated by high-density and low-density shadows. The higher the relative hardness, the higher the density on the dental film, showing a high-density shadow, which appears white, while the lower the relative density, the lower the hardness, which appears black. The whitest colored high-density shadow on a dental film is enamel, followed by dentin and osteoid, while the alveolar bone is also a high-density image. The relatively low-density images on the radiograph are air, soft tissue, and caries, which are less dense than the high-density images and appear exactly where the high-density corresponds to the caries.