Measurement · CONVEX
Angle of convexity (N-A-Pog)
Loading the reference ceph.
Definition
How far A point deviates from the straight facial line N–Pog: the angle between N→A extended and A→Pog. Positive = convex (A ahead of the line), negative = concave.
How
Draw N–A and A–Pog. Extend N–A beyond A; the angle between that extension and A→Pog is the convexity (0° = perfectly straight profile).
Purpose
Downs' shape read of the midface: it catches maxillary protrusion OR mandibular retrusion as one 'profile bend' number. Strongly convex profiles read Class II; concave profiles Class III.
High
Above the norm reads as a convex skeletal profile — A point bulges ahead (Class II pattern).
Low
Below the norm reads as a concave skeletal profile — the midface sits behind the chin line (Class III pattern).
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Angle of convexity (N-A-Pog) here is a real reading and not a diagram.