Table 1.

PICOS description.

Population	Clinical patient studies that evaluated the effects of specific rapid maxillary expansion on the volume of the nasopharyngeal airway
Intervention	Rapid maxillary expansion evaluated via cone beam computed tomography
Comparison	Age- and sex-matched subjects who did not undergo rapid maxillary expansion therapy
Outcome	Changes in the dimensions of the nasopharyngeal airway
Study design	Randomized and nonrandomized controlled trials and observational studies. Case reports and author's opinion publications were excluded