Children’s teeth are completely replaced and the age of tooth replacement is around 6-12 years old. Children’s baby teeth are fully grown in around 3 years of age, so parents must distinguish between what is baby teeth and what is permanent teeth. There are 20 baby teeth, five on the top, five on the bottom, five on the left and five on the right. At the age of 6, children will have their first permanent tooth, which is located at the end of all baby teeth and is the first big tooth. Many parents will mistake it as milk tooth and do not protect it, which eventually leads to premature decay or premature loss of this tooth, and this tooth is often the key to jaw building during the period of tooth replacement, so parents must go to the pediatric dentist in time when the child enters the period of tooth replacement, and perform sulcus closure on this tooth to prevent the occurrence of tooth decay.