Measurement · FDEPTH
Facial depth (Ricketts)
Loading the reference ceph.
Definition
The inferior-posterior angle between the Frankfort horizontal and the facial plane (Nasion–Pogonion). Downs' primary measure of chin position.
How
Draw Frankfort horizontal (Po–Or) and the facial plane from Nasion (N) down to Pogonion (Pog); read the angle at their intersection. A prognathic chin carries the facial plane forward and the angle above 90°.
Purpose
Ricketts' facial-depth read: chin position against Frankfort, expected to increase ~0.3°/year with normal growth. Low values flag the retrognathic (Class II) pattern his mandibular-growth prediction targets.
High
Above the norm reads as a prominent, anteriorly positioned chin (mandibular prognathism / skeletal Class III tendency).
Low
Below the norm reads as a retruded chin (retrognathic mandible / skeletal Class II tendency).
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Facial depth (Ricketts) here is a real reading and not a diagram.