It is normal for normal babies to start teething at 6 months of age, and it is normal for late teething to occur at 10 months of age. If the teeth do not appear more than 10 months, it is called “late eruption of milk teeth” in medical science. The whole process of tooth development is closely related to the internal and external environmental factors of the body. The most common cause of delayed eruption of milk teeth is calcium deficiency, which is medically known as vitamin D deficiency rickets. The malfunction of calcium and phosphorus metabolism in children caused by vitamin D deficiency delays the development of the tooth germ, resulting in late eruption of the milk teeth. In addition to calcium deficiency, endocrine metabolic disorders, such as hypothyroidism (cretinism), can also prevent tooth germ formation and delay tooth emergence. In addition, neurological disorders and certain infectious diseases, as well as congenital skeletal hypoplasia, impair the process of tooth growth and development, calcification, and eruption. There is also a rare disease DD congenital edentulism reported, which refers to edentulous malformation without a single tooth in life. In addition to edentulism, the patient is not often accompanied by underdevelopment of hair, nails, sebaceous glands and sweat glands. When an infant is teething, especially if it is more than 1 year old and has not yet teething, it cannot be denied that it must be due to calcium deficiency, and the child must be blindly given calcium supplements; he must be taken to the hospital for a comprehensive examination to identify the cause and be treated by the doctor for the right condition. The growth and development of children’s teeth starts from the early fetal stage, specifically from 6 weeks after the mother’s pregnancy. In order for a child to grow a set of healthy teeth, health care must be done from the pregnancy period. It is important to ensure that pregnant women, lactating mothers and infants receive adequate daily intake of protein, vitamins and various minerals, strengthen physical exercise, get more sunlight and, in particular, take calcium supplements. Giving 4-5 months old children some dried bread and hard cookies can exercise the dental bed and facilitate the development of the child’s jawbone and the eruption of milk teeth.