Some children have a very high rate of caries, almost all the teeth in the mouth have caries. During the examination, the doctor found yellowish-white plaque on the surface of the child’s teeth and even enamel defects, and told the parents that “your child’s teeth may have lacked calcium during development, thus causing poor enamel calcification. It is only because of the poor quality of teeth that they are prone to caries.” Parents often reply, “Then I’ll start giving my child calcium supplements now.” Is it useful to give calcium supplements after the teeth erupt? It is necessary to know when the calcification of enamel on the tooth surface is completed. Teeth develop through three stages: anagenesis, calcification and eruption. The formation of all the hard tissues of the milk teeth starts in the fetal period and is completed within one year after birth at the latest. The permanent teeth, except for the six-year-old teeth, have a small portion of cusp calcification in the newborn, but the rest begin to calcify after birth, and by about 7 or 8 years of age, the enamel of all permanent tooth crowns except the third permanent molar has been calcified. Therefore, the calcification of enamel is completed before the teeth erupt. Moreover, the calcification of tooth enamel starts from the outside to the inside, and the enamel on the surface of permanent teeth is already calcified by the age of three. Therefore, oral calcium supplementation after the teeth erupt has little effect on the erupted teeth, but can have an effect on the tooth germ that is in the stage of enamel calcification. For your child to have well-developed teeth, calcium supplementation should start during pregnancy, pay attention to balanced nutrition, strengthen resistance, and prevent systemic diseases, especially viral infections, especially within the age of three. In addition, chronic apical inflammation of the milk teeth and dental trauma can also have an impact on the calcification of the enamel of permanent teeth and should be treated early.