Every parent wants their child to have healthy, white, well-aligned teeth. However, although many children have neatly aligned teeth during the period of milk teeth, various problems appear during the replacement process, such as crowding, twisting, reversal, ectopic eruption, eruption difficulties and other malocclusions. This can cause a lot of trouble and pain for parents and children. As a matter of fact, many malocclusions can be prevented and reduced if they are prevented and treated in time during the period of the baby teeth. Parents often ask: Why does my child have gaps in his teeth? In fact, more than 80% of children have gaps in their teeth during the milk teeth period. The maintenance of this gap is very important for the normal development of the face and the fit, which can induce normal eruption of the inherited permanent teeth and a good occlusal relationship, and prevent occlusal disorders caused by insufficient gap. Even for children with malocclusion, if the gap is maintained, it can reduce the severity of malocclusion during permanent tooth replacement and reduce tooth extraction during permanent tooth orthodontic treatment. Generally, the loss of space between milk teeth is caused by caries, so we should pay attention to the prevention and treatment of caries. If the milk teeth are lost due to caries or other reasons, it is necessary to consult the doctor in time and choose the appropriate type of gap retainer. The most common occlusal disorder in children during the period of milk teeth is the anterior or posterior teeth retrusion. The treatment of milk teeth inversion can improve the occlusal relationship and the covering relationship of the front teeth, and prevent the development of the maxilla from being restricted, forming the so-called “crescent face”. After the treatment of most of the anterior molar retrusion, the permanent teeth do not retrude during tooth replacement, and even if a small amount of retrusion occurs, the treatment can be easily performed again. The recoil of the milk molars is mostly detected by the doctor during the examination and should also be treated as early as possible during the milk teeth. Generally speaking, the best time to treat milk teeth recoil is mostly around the age of 4 years. The treatment time does not exceed 3 months. There are many causes of malocclusion in childhood, but bad oral habits are one of the most important ones. There are a variety of bad habits in children, and long-term accompanying bad habits can cause malocclusion. Common bad habits include finger sucking, tongue spitting, lip biting, mouth breathing, night grinding, lateral chewing and so on. These bad habits can cause changes in the oral muscles and dentition after the age of 4. Parents should consult a doctor as soon as they discover these bad habits, determine the cause with the assistance of the doctor, and take appropriate care and psychological guidance so that the child can give up the bad habits as soon as possible. If they cannot overcome them after the age of 6, they should adopt the appropriate orthodontic appliances to help the child stop the bad habits.