There are many types of orthodontic appliances, which are generally selected according to the method of correction of malocclusion, and there are four general categories: movable appliances: can be freely removed by the patient from the mouth, often used for minor tooth movement and to improve minor malocclusion, or as a retainer after the completion of orthodontic treatment. They are used, for example, for the correction of simple malocclusions during the period of milking and replacement teeth, or in conjunction with fixed orthodontic appliances, and the effectiveness of the treatment relies heavily on the cooperation of the patient. In addition, in recent years, a “bracketless invisible orthodontics” technology has emerged, which is the product of a perfect combination of modern computer-aided three-dimensional diagnosis, rapid prototyping technology and new materials. Through the computer simulation of the orthodontic process, and the use of elastic transparent polymer material for each stage of tooth movement to create a free removable braces, the patient wears a series of braces in order to achieve the purpose of orthodontic treatment. However, the indications for “bracketless invisible orthodontic treatment” are more strict and are currently only applicable to some simple cases. Fixed aligners: As the name implies, fixed aligners that cannot be removed by the patient can do a wide range of tooth movement and change the position of crowns and roots. Currently more than 90% of patients use fixed aligners, which are mounted on the teeth by the doctor with special medical adhesive and are more efficient than removable aligners. Currently there are various types of fixed aligners, based on the material, there are stainless steel (obvious appearance, is commonly known as “iron mouth steel teeth”), transparent ceramic, transparent resin (transparent material and tooth color close to the more beautiful, but relatively expensive) and other types; based on the location of the bonding, there are placed on the outside of the teeth of the lip side of the aligner. This type of aligner is the most, there are also lingual aligners placed inside the teeth, many actors will choose this completely invisible aligner, because it is completely invisible from the outside, to achieve a very hidden effect, but the discomfort of the first wear may be more obvious, the technical requirements are also higher than the lip side aligners. Functional orthodontic appliances: also belong to the patient can take off the movable orthodontic appliances, mainly used in the period of teeth replacement or just after the replacement of teeth is still in the growth spurt of children, can correct some bony malocclusion, the effect depends on the patient’s cooperation and their own growth and development, after the completion of treatment, often also need to resort to fixed orthodontic treatment. Extra-orthodontic braces: They are also a type of aligner that can be removed by the patient, and are mainly used to correct some skeletal malocclusions during the growth phase, and are sometimes used to assist in the movement of teeth for adult patients.