The exchanges of heat, whose nasal mucosa is the instrument, play indirectly a prominent role in human brain thermoregulation. Their alteration by nasal obstruction is the source of sleepy and behavioral problems : these disorders cease as soon as exclusively nasal ventilation at rest and when sleeping is
From these data, «optimal nasal ventilation» is put forward as an operative physiological definition. They allow a better understanding of malocclusion etiology. They specify the objectives to be reached thanks to dentofacial orthopedics.