[Nasal respiration and recurrence].

Cause and effect relationships existing between "nasal breathing impairment" and "relapse" have inherited from controversies which have animated the debate between the different schools of orthodontics for more than a century. Those differences of opinion seem to have their origin in the lack of accuracy inherent with the general acceptance of the two concepts of "normal nasal ventilation" and "relapse". Rather than retracing their history, we would like to put forward a few proposals aimed at getting rid of the doubtful trouble the present difficulty confronts us with. We have therefore endeavored: 1. to define most exactly our concepts of "optimal nasal ventilation" and "relapse"; 2. to determine, afterwards, the mechanics responsible for facial shape alterations due to nasal obstruction; 3. hence, to deduce the therapeutic behavior enabling us to master those alterations more extensively. Bearing in mind that, in order to legitimate the risk of a treatment, acknowledge its benefit and justify its cost (which may become prohibitive because of relapse), the clinician has to base his options on a body of consistent arguments.