Under normal circumstances, tooth replacement starts at the age of 5~7 years old, and permanent teeth will replace milk teeth one by one at the age of 6~12 years old. People will have two sets of teeth in their lifetime, milk teeth and permanent teeth. Milk teeth erupt 6~10 months after birth, and then they will go through the period of tooth replacement when the permanent teeth replace the milk teeth. Generally, the first teeth to erupt are the first permanent molars, which are located after the second milk molars, and are called the six-year-old teeth because they erupt around the age of six. At the same time, or a little later, the permanent mesial incisors will erupt to replace the milk mesial incisors, followed by the posterior lateral incisors and the first premolars, etc. The replacement of milk teeth is a physiological phenomenon, but the replacement of milk teeth is a physiological phenomenon. Tooth replacement is a physiological phenomenon, but during tooth replacement, symptoms such as low fever, irritability, increased salivation, and sleep disturbance may occur, and if these symptoms occur, timely consultation should be made. Attention should also be paid to protecting children’s dental health by reducing sweet foods and brushing their teeth regularly.