When a child reaches the age of 6, the first permanent molar erupts behind the milk molar, and then the milk teeth begin to fall out and the succeeding permanent teeth erupt in the corresponding position, and all the milk teeth are replaced by the age of about 12. At this stage (6-12 years old), there are both permanent and baby teeth in the mouth, which is called mixed dentition, or what we often call the period of tooth replacement. It is also a critical period for the permanent teeth to establish a new occlusal relationship. Therefore, the correct understanding and treatment of the common phenomenon of the teething period is particularly important for the oral care of children at this stage. In general, the following changes will occur during the period of teeth replacement – 1. Small gaps between the newly erupted central incisors or tilt to the sides. Children around 6 years old, just replaced the upper incisors (incisors) often do not come together, the middle of the gap, many parents often bring their children to consult the need for orthodontics. This phenomenon is the result of the root end of the lateral incisors on both sides pressing the root end of the incisors so that the root is tilted toward the proximal center and the crown is tilted toward the distal center, and the gap will close on its own when the two lateral incisors erupt. 2. Mild crowding of incisors at the early eruption of permanent incisors. Usually, the newly erupted permanent teeth are larger than the replaced baby teeth. In the early stage of lower incisor eruption, because the replacement gap is not enough to accommodate the relatively large permanent teeth, mild crowding of the lower front teeth may occur, and the crowding will be improved later with the growth of jaw bone and alveolar process. 3, early eruption of the upper and lower permanent incisors, the anterior teeth appear mild deep overlap relationship. That is, the incisive edge of the upper front teeth covers the lower front teeth below 1/3 of the labial surface. This is a temporary phenomenon of mild deep overlap because the molars are not fully erupted and the occlusal height is not high enough. Later, as the permanent molars erupt and achieve occlusal contact, this phenomenon will disappear on its own. The period of tooth replacement is a critical period for children’s growth and development, and is directly related to whether the child’s future teeth are neat and the face is beautiful. Parents should pay close attention to the eruption and replacement of your child’s teeth and go to the hospital for regular checkups so that your child has healthy teeth and a beautiful face.