Measurement · L1APOGMM
L1 to A-Pog (mm)
Loading the reference ceph.
Definition
The perpendicular distance from the lower incisal tip to the A–Pogonion line — Ricketts' key lower-incisor position target.
How
Draw A–Pog (the denture line); drop a perpendicular from L1T; read in mm anterior (+) to the line (target ≈ +1 mm ± 2).
Purpose
THE Ricketts finishing target: the lower incisor should sit ~1 mm ahead of A–Pog for a balanced profile and stable result. It converts 'where should the lower incisor end up' into one number that drives space analysis (each mm of advancement gains ~2 mm of arch length).
High
Above the norm reads as lower incisors protrusive to the denture line — profile fullness, stability/periodontal risk if advanced further.
Low
Below the norm reads as lower incisors retruded — flat profile; space analysis gains room if advanced toward the target.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so L1 to A-Pog (mm) here is a real reading and not a diagram.