Measurement · ARTIC
Articular angle (S-Ar-Go)
Loading the reference ceph.
Definition
The second Björk polygon angle: at Articulare, between the line up to Sella and the posterior border of the ramus (down to Gonion).
How
At Ar, measure the angle between Ar→S and Ar→Go (norm ≈ 143°).
Purpose
The one polygon angle mechanics can actually change (it closes as the mandible is repositioned forward, opens with distalization). A large articular angle accompanies retrusion of the mandible; a small one forward posturing/prognathism.
High
Above the norm reads as the ramus swings back from the cranial base — mandibular retrusion, vertical tendency.
Low
Below the norm reads as the ramus stands forward — prognathic/horizontal tendency.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Articular angle (S-Ar-Go) here is a real reading and not a diagram.