Measurement · L1NBmm
L1 to N–B (mm)
Loading the reference ceph.
Definition
The perpendicular distance from the lower incisor's tip to the N–B line — the lower incisor's bodily prominence.
How
Drop a perpendicular from the L1 incisal tip (L1T) onto N–B; read in mm, positive anterior to the line (norm ≈ 4 mm).
Purpose
Bodily read of lower-incisor prominence. Classically balanced against Pog–NB (Holdaway wanted them roughly equal): incisors much more prominent than the chin read as dental protrusion the profile will show.
High
Above the norm reads as the lower incisor sits bodily forward of the mandibular line.
Low
Below the norm reads as the lower incisor sits back on its base.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so L1 to N–B (mm) here is a real reading and not a diagram.