Table 1.

Definition of Landmarks and Reference Planes Used for the Assessment of Changes in Dimensions of the Nasal Airway After Nonsurgical Miniscrew-Assisted Rapid Maxillary Expansion

Definition	Description
Landmark
ANS	Anterior nasal spine: a bony protrusion extending forward at the base of the nasal aperture
Choanae	The choanae are bounded medially by the vomer, inferiorly by the horizontal plate of the palatine bone, laterally by the medial pterygoid plate, and superiorly by the body of the sphenoid bone1
C3	The most inferior and anterior point on the third cervical vertebra
Reference planes
FH plane	Frankfort horizontal plane, which is determined by both porions and left orbitale
C3 plane	Parallel to the FH plane and passing through C3
ANS-perp. plane	Perpendicular to the FH plane and passing through ANS
Choanae plane	The plane along the choanae

ANS, choanae, C3, FH plane, C3 plane, ANS-prep. plane, and choanae plane were identified on two-dimensional lateral cephalograms reconstructed from three-dimensional cone beam computed tomography (CBCT) images.