Bone expansion generally refers to orthodontic arch expansion. If an eight-year-old child is in the period of tooth replacement, orthodontic expansion is generally not recommended; to the end of the replacement of teeth such as the existence of dental crowding, orthodontic expansion can be considered. 1. At the age of 6~8 years old, during the period of tooth replacement, milk teeth begin to loosen and fall off, and are gradually replaced by permanent teeth. At this time, the new permanent teeth may not be very neat, but the child’s teeth and bones are not the same almost every day, and with time the permanent teeth will gradually grow into their own position, and finally gradually aligned. 2. If the teeth are still crowded at the end of the tooth replacement period, you can take your child to the clinic to clarify the need for orthodontic treatment. Generally, adequate space can be obtained by expanding the width of the abutment bone and the dental arch, so that the teeth can be aligned and stabilized. If the child is in need of orthodontic treatment, it is recommended that parents take their child to a regular hospital to have the condition of crowded teeth evaluated through imaging, measurement, and localized examination, and the doctor will provide targeted treatment.