The strength of the orthodontic force is divided into light force, medium force and heavy force, which should be chosen according to the doctor’s prescription. 1. Mild orthodontic force: the strength is about sixty to one hundred grams, and the strength is light (mainly including elastic rubber bands, etc.); it can mainly make the teeth move to a certain extent. 2. Medium orthodontic force: the strength is about one hundred to three hundred grams, and the tools for generating medium orthodontic force mainly include archwires or spring bends, etc., which are also mainly used for tooth movement. 3. Heavy orthodontic force: the strength is generally greater than three hundred grams, which can affect the growth of bones during the growth period to change the shape of the jaws; in turn, it can lead to the normal development of the maxillofacial shape, and the main tools include extra-oral anterior retractors, extra-oral arches and so on.