RESUMEN
The present study was conducted to evaluate the effect of rapid maxillary expansion [RME] the primary nocturnal enuresis [NE]. A sample consists of 19 patients, with resistant primary nocturnal enuresis, aged 6-15 years, treated by banded Hyrax expander in the College of Dentistry University Baghdad, 7 patients out of study group considered as control group at first to exclude placebo effect of the appliance. CT scan was used to evaluate the increase in the nasal cavity width at the level of inferior choncha, rhinomanometry used to assess nasal airflow and nasal resistance, osmolality measured to evaluate plasma antidiuretic hormone [ADH] all these parameters done before and 2-3 months at expansion in Al-Kadhymia Teaching Hospital. Patients in the study group underwent rapid maxilla expansion in 10-15 days, after 2 to 3 months of expansion most of the patients show complete dryness and others show notable improvement in nocturnal enuresis. The improvement in nocturnal enuresis following rapid maxillary expansion may be due to: -1-Restoration of normal sleep patterns, that make the patient wake easily, this caused by improvement nasal breathing, snoring, deep sleep, and treatment of mouth breathing following rapid maxilla expansion. -2-Increase in the antidiuretic hormone secretion, that causes decrease in the plasma osmolality and urine production following rapid maxillary expansion