Tooth decay, also known as worm teeth, is a disease caused by bacterial infection of the hard tissues of the teeth, which causes decay and disintegration of the hard tissues of the teeth, and the hard tissues on the dental film are generally compared with the surrounding hard tissues, and generally the hard tissues on the dental film show high density images, that is, white images. The enamel, as the hardest material in the body, shows the highest density image on the dental film, followed by the dentin, and the lowest density image is the alveolar bone, because it is more loose. If there is a low density image among them, and it is located completely in the enamel and dentin, it is generally considered as caries, and we can check the specific situation of caries according to the extent and depth of the shadow.