Measurement · JGONIAL
Gonial angle (Ar-Go-Gn) — Jarabak
Loading the reference ceph.
Definition
The mandible's own angle at Gonion between ramus (Go→Ar) and body (Go→Gn); the third angle of the Björk polygon.
How
At Gonion, measure between Go→Ar and Go→Gn. In the Björk–Jarabak analysis it joins the saddle and articular angles; their sum sets the growth-direction read.
Purpose
Within Jarabak's polygon this is the biggest lever on the sum of angles: an obtuse gonial angle drives the sum above 396° (clockwise/vertical growth prediction), an acute one below (counterclockwise/horizontal).
High
Above the norm reads as an obtuse angle — vertical (clockwise) growth prediction.
Low
Below the norm reads as a square angle — horizontal (counterclockwise) growth prediction.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Gonial angle (Ar-Go-Gn) — Jarabak here is a real reading and not a diagram.