Measurement · GON
Gonial angle (Ar-Go-Gn)
Loading the reference ceph.
Definition
The angle of the mandible itself: at Gonion, between the ascending ramus (toward Articulare) and the mandibular body (toward Gnathion).
How
At Gonion (Go), measure between Go→Ar (posterior border of the ramus) and Go→Gn (lower border of the body).
Purpose
Describes mandibular morphology and growth direction: an obtuse gonial angle unrolls the mandible into a vertical, long-faced pattern; a square (acute) angle rolls it forward into a horizontal, deep-bite pattern. Also flags how much bite-opening the mandible will tolerate.
High
Above the norm reads as an obtuse mandibular angle — vertical grower, long lower face, weak chin projection.
Low
Below the norm reads as a square mandibular angle — strong horizontal grower, deep-bite/brachyfacial pattern.
Built from
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Gonial angle (Ar-Go-Gn) here is a real reading and not a diagram.