Malocclusion is a developmental malformation in which the relationship between the teeth, dental arch, jawbone and craniofacial surface is out of alignment, which is a professional theoretical concept. Simply put, malocclusion is when the position of the teeth is different from the normal position, making the teeth’s occlusal relationship uncoordinated. The boundary between malocclusion and normal dentition is not distinct, it is a quantitative to qualitative development process. Generally speaking, we include in the category of normal malocclusion any minor tooth position irregularities that are not too much of an obstacle to the physiological functions of chewing, swallowing, pronunciation and aesthetics. Thus, there is no strict boundary between malocclusion and normal dentition. The prevalence of malocclusion is very high, specifically in our country, in 2003, the prevalence of malocclusion was 67.82% in a survey of 25,392 young children in China, led by the Peking University Dental Hospital. There are various manifestations of malocclusion, both simple and complex. The first type is the misalignment of individual teeth, the specific clinical manifestation of which is the misalignment of teeth. The second category is the arch morphology and teeth alignment abnormalities, the specific clinical manifestations are the dental arch is too wide, too narrow, teeth crowding due to insufficient gap (multiple teeth are not aligned), sparse teeth – that is, the teeth are not closely aligned with each other, and gaps appear between teeth and teeth. The third major category is the abnormalities of the dental arch, jawbone, and craniofacial relationship, the main manifestations of this major category are: enamel (the normal situation is that the upper teeth are in front of the lower teeth, but in enamel patients, the lower teeth are wrapped around the upper teeth, i.e., the lower teeth are in front of the upper teeth, and such patients generally have larger lower jawbones), protrusion of teeth (often manifested as upper front teeth, somewhat like rabbit teeth), anterior open bite (gaps between upper and lower teeth, bite This kind of patient often gives a feeling that the face is particularly long), and there is another kind of malocclusion that looks like a shorter face. There are many other manifestations, so I will not describe them in detail here.