Mouth breathing habits are frequently associated with orthodontic problems. In the nasal area, the lack of ventilation leads to an underdevelopment of the maxilla: lateral and sometimes anterior cross bites appear. In the buccal area, the want of maintaining the mouth opened induces a new postural position of the mandible which alters the pattern of growth of the mandible ("long face"). The functional context of the buccal praxis is also altered: low or protruded tongue, deviant swallowing, troubles of speech.... The treatment of this pathological context needs a pluridisciplinary approach where the otorhinolaryngologist, the dentist, the orthodontist and the speech pathologist have to play an important role. In the orthodontic fields, we have to carry out an orthopedic treatment (rapid maxillary expansion, facial masks,...) to normalize the growth of the maxilla before the orthodontic treatment.