The timing of tooth eruption is not the same for infants and toddlers due to their different development and there is generally no fixed time. Usually, baby teeth start to erupt at 6-7 months of age. However, some babies may have their baby teeth erupt 4 months after birth, and some babies may have their baby teeth erupt 10 months after birth, which is normal. Starting from the eruption of the incisors in the lower jaw, the teeth will grow at a rate of one more per month, with 6 teeth growing in about 12 months and all 20 milk teeth erupting at about 2.5 years of age. Clinically, the development of teeth, as well as the timing and order of eruption, is often used to reflect the skeletal development of children. Generally, children with good skeletal development can have timely teething and good quality teeth. On the contrary, children with poor skeletal development will also have delayed teething time. Generally, it is normal for children to erupt their first milk teeth within 1 year old. If a child has not yet erupted his first milk tooth beyond 1 year of age, he is considered to have late teething, and if he has not yet erupted all his milk teeth beyond 3 weeks of age, he is considered to have late teething. In this case, it is necessary to consider whether there are physical abnormalities, such as rickets, hypothyroidism, malnutrition, cretinism, etc. It is recommended to consult a doctor for examination as soon as possible.