Landmarks and reference lines used for orofacial airway space: Pt (pterygoid point), the posterior point of the pterygopalatine fossa; ANS (anterior nasal spine), anterior point of the maxilla; PNS (posterior nasal spine), posterior point of the palatine bone; Me (Menton), the inferior point of the symphysis; H1, intersection between the posterior border of the tongue and the hyoid bone; H2, the most anterior point of the hyoid bone; T, the most anterior point of the outline of the tongue; palatal plane, a line passing through the ANS and PNS.