Measurement · L1NB
L1 to N–B (angle)
Loading the reference ceph.
Definition
Steiner's lower-incisor inclination: the angle between the lower incisor's long axis and the N–B line.
How
Draw N→B and the L1 long axis (L1A→L1T); measure the angle between them (norm ≈ 25°). Pair with the L1–NB mm value for bodily position.
Purpose
Positions the lower incisor against the mandible's diagnostic line. With Pog–NB it forms Holdaway's ratio idea (incisor prominence should balance chin prominence).
High
Above the norm reads as proclined lower incisors relative to N–B.
Low
Below the norm reads as retroclined lower incisors relative to N–B.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so L1 to N–B (angle) here is a real reading and not a diagram.