Figure 1. Landmarks and reference planes. S, Sella; N, Nasion; Po, Porion; Or, Orbitale; Co, Condylion; Ar, Articulare; ANS, anterior nasal spine; PNS, posterior nasal spine; A, Point A; B, Point B; U1E, incisal edge of maxillary central incisor (U1); U1A, root apex of U1; L1E, incisal edge of mandibular incisor (L1); L1A, root apex of L1; Pog, Pogonion; Gn, Gnathion; Me, Menton; Go, Gonion; Sella-Nasion plane (SN plane), line from S to N; Frankfort horizontal plane (FH plane), line from Po to Or; Palatal plane, line from PNS to ANS; Functional occlusal plane, line drawn along the maximum intercuspation of the posterior teeth; N-perpendicular plane (N-perp plane), perpendicular line to FH plane passing through Nasion; Facial plane, line from N to Pog; Mandibular plane, line from Go to Me.