First of all, what is a crooked face? The textbooks call it “facial skew”. The face of a normal individual is not completely symmetrical, and some asymmetry does not affect the overall beauty and coordination of the figure. Only when the asymmetry exceeds 10%, or the difference between the left and right sides is greater than 2mm, is it considered an asymmetrical deformity, i.e. facial deviation, mainly in the lower face, i.e. lower jaw deviation or chin deviation. The prevalence of facial deviation: 2.6-6.4% among orthodontic patients. A large percentage of these patients, including the parents themselves, may not be aware of the facial deviation at the time of the initial consultation, but are identified by an experienced orthodontist. Due to the influence of hair style, glasses, posture and facial expressions, a slight deviation is overlooked by many people, including, of course, some so-called orthodontists. It is only when the deviation gets worse and becomes obvious that it becomes easily visible. So what causes facial obliquity? Its etiological mechanism is complex and unclear, currently four kinds of etiological classification are recognized: 1, dental type Due to malocclusion or occlusal factors, due to early loss of milk teeth, congenital missing teeth, or due to finger-sucking, lateral chewing and other oral habits caused by both sides of the dental arch asymmetry or upper and lower dental arch mismatch, in order to avoid interference, the lower jaw is shifted to one side when biting, forming the lower jaw Skewing. 2. Functional Due to finger sucking, cheek sucking habit, abnormal swallowing, mouth breathing, chronic rhinitis, and adenoid/tonsil hypertrophy, etc., the maxillary arch is narrowed, resulting in occlusal interference, and in order to avoid interference, the lower jaw is shifted to one side during occlusion, resulting in mandibular obliquity. 3. Bony i.e. true asymmetry, congenital asymmetry in the development of the left and right side of the maxilla or mandible. Bilateral asymmetry of the condyle, articular fossa and both sides of the mandible due to developmental differences between the left and right sides (differences in size, length and growth rate), condylar osteoma, condylar fracture, trauma, chronic inflammation, etc. are common causes of bony asymmetric deformity. 4.Muscle type Asymmetry of neck muscles directly causes asymmetry of bone growth. Studies have shown that oblique neck, sternocleidomastoid and latissimus dorsi muscle hyperfunction can cause facial obliquity. There is also an association between cervical spine postural position and facial deviation. The first two causes, i.e., dental and functional facial deviation, should be treated as early as possible to eliminate occlusal interference and bring the movement of the jaws into proper alignment as soon as possible. Otherwise, the asymmetric deformity may continue to worsen with growth and development, and eventually develop from a dental or functional asymmetric deformity to a bony asymmetric deformity. And bony skew, due to growth and developmental deformity, with age, the asymmetry will aggravate the magnification becomes obvious, and can not be improved because of orthodontic teeth, contrary to expectations will only appear worse end — “the more corrected the more skewed”, in the final analysis actually has nothing to do with orthodontics, except that the most obvious process of growing skewed occurs in the best orthodontic The most obvious process of growth deviation occurs at the best age for correction. The boy’s growth peak is 14 years old, and the growth of the skew can continue even into the 20s. The ultimate means for the bony type is orthognathic surgery after the growth of the skew has stopped. As for the muscular type, the onset of the muscles should be promptly treated with relaxation surgery, correcting the cervical posture is imperative, and then with orthodontic treatment to correct the dental deviation. As the mandibular deviation can make the condyle position abnormal. It is easy to cause hazomandibular joint disorder. Serious facial deviation not only affects the aesthetics of the patient’s face, occlusal function and the health of the temporomandibular joint, but also brings psychological damage, causing low self-esteem and depression.