When the enamel is abraded, it reveals the dentin and is light yellow. Tetracycline teeth 1, yellow, in the sunlight is bright yellow fluorescence, and later gradually from yellow to brown or dark gray. This transformation is slow and can be promoted by sunlight, so the lip surface of incisors is the first to change color. 2, the front teeth than the back teeth coloring obvious; milk teeth coloring than permanent teeth obvious, because milk teeth enamel is thin, more transparent, not easy to cover the color of the tetracycline conjugate in dentin. 3, the degree of tooth coloring and tetracycline type, dose and the number of times the drug is given. It is generally believed that the coloration caused by shrunken tetracycline, desmethyl chrysomycin, tetracycline hydrochloride is more pronounced than that of hygromycin and chrysomycin. In permanent teeth, the number of courses of tetracycline is positively related to the degree of coloration, but a short period of high dose administration is more effective than an equal total dose given over a long period of time. 4, Tetracycline causes tooth coloration and enamel hypoplasia, both of which are only apparent when given during tooth development. Generally speaking, after 6 to 7 years of age and then give the drug, it does not cause striking tooth discoloration. Dental caries: A disease in which the enamel, dentin, or bone of the teeth undergoes progressive destruction under the influence of external factors. Milky teeth: Milky teeth are autosomal dominant and can occur in a family for several generations, but can also be passed on from generation to generation. If one of the two parents is a patient with the disease, the number of children with the disease is about half of the patients, the incidence of both sexes is equal, and both milk and permanent teeth can be involved. Milky teeth can coexist with osteogenesis imperfecta (brittle bone fracture, blue sclera, otosclerotic deafness), albinism and cardiac malformations. Pigmentation: generally deposited on the surface of the crown of the plaque, tartar, soft tartar and pigment (smoke, tea) stains, often the lingual surface of the teeth than the lips and cheeks of the heavier, mandibular teeth heavier than the maxillary teeth. Careful observation can be seen attached to the surface of the teeth, external forces can be removed.