Measurement · U1NAmm
U1 to N–A (mm)
Loading the reference ceph.
Definition
The linear distance from the upper incisor's tip (its most labial point) to the N–A line — the bodily (not tip) position of the upper incisor.
How
Drop a perpendicular from the U1 incisal tip (U1T) onto the N–A line; the distance is read in mm, positive when the tip sits anterior to the line (norm ≈ 4 mm).
Purpose
Separates bodily protrusion from mere tipping: a normal U1–NA angle with a large mm value means the whole tooth (and its alveolus) is forward. Guides whether retraction should be bodily (torque control) or tipping.
High
Above the norm reads as the upper incisor is bodily forward of the maxillary line (dentoalveolar protrusion).
Low
Below the norm reads as the upper incisor is bodily retracted toward/behind N–A.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so U1 to N–A (mm) here is a real reading and not a diagram.