Measurement · L1OCC
L1 to occlusal plane
Loading the reference ceph.
Definition
The angle the lower incisor's long axis makes with the occlusal plane (Downs reports the deviation from perpendicular).
How
Draw the occlusal plane and the L1 long axis (L1A→L1T); measure their crossing angle (norm ≈ 14.5° from perpendicular).
Purpose
Grades lower-incisor tip against the functional plane: more tip = proclination relative to the bite plane (protrusion/compensation), less = upright incisors.
High
Above the norm reads as lower incisors tipped forward relative to the biting plane.
Low
Below the norm reads as lower incisors upright against the biting plane.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so L1 to occlusal plane here is a real reading and not a diagram.