A 18 years old male patient, complains of inability to close the lips and history of adenoidectomy 1 month ago. General physical examination reveals increased anterior facial height and incompetent lips. Intraoral findings suggest narrow maxillary arch. These features are seen in patients with-

Respiratory needs are the primary determinant of the posture of the jaws and tongue (and of the head itself, to a lesser extent). Therefore it seems entirely reasonable that an altered respiratory pattern, such as breathing through the mouth rather than the nose, could change the posture of the head, jaw, and tongue. This in turn could alter the equilibrium of pressures on the jaws and teeth and affect both jaw growth and tooth position. To breathe through the mouth, one must lower the mandible and tongue and extend (tip back) the head. If these postural changes were maintained, three effects on growth would be expected: (1) anterior face height would increase, and posterior teeth would super-erupt; (2) unless there was unusual vertical growth of the ramus, the mandible would rotate down and back, opening the bite anteriorly and increasing overjet; and (3) increased pressure from the stretched cheeks might cause a narrower maxillary dental arch. Chronic respiratory obstruction can be produced by prolonged inflammation of the nasal mucosa associated with allergies or chronic infection. It can also be produced by mechanical obstruction anywhere within the naso-respiratory system, from the nares to the posterior nasal choanae. Under normal conditions, the size of the nostril is the limiting factor in nasal airflow. The pharyngeal tonsils or adenoids normally are large in children, and partial obstruction from this source may contribute to mouth breathing in children. Individuals who have had chronic nasal obstruction may continue to breathe partially through the mouth even after the obstruction has been relieved. In this sense, mouth breathing can sometimes be considered a habit.