Correction of crowding of the upper row of teeth, the principle is generally to increase the amount of bone and reduce the amount of teeth: 1, can increase the length of the dental arch, can be pushed molar teeth backward or labial inclination of anterior teeth; 2, increase the width of the dental arch, can be through the palatal mesial gap extension to increase the width of the arch or orthodontic arch expansion; 3, can be through the dental arch, alveolar bone functional expansion to increase the amount of bone and reduce the amount of teeth, generally through the neighboring surface de-glazed to reduce the teeth of the proximal and distal Median diameter; 4. Reduction of tooth volume by extraction and reduction treatment. Through the above methods, crowding of the maxillary dental arch can be corrected. The doctor will choose the appropriate method according to the patient’s situation.