Table 1. Definition of landmarks used in this study.

Symbol	Definition
Gn	The midpoint between the most anterior and inferior points on the outline of the mandibular symphysis
Me	The most inferior point on the outline of the mandibular symphysis
H	The most anterior and inferior point of the hyoid bone
C3	The most anterior and inferior point of the third cervical vertebra
C3-Me line	The line connected between point C3 and point Me
CSA	The cross-sectional area of the upper airway on each CBCT sagittal plane