Measurement · SNH
Subnasale to H-line
Loading the reference ceph.
Definition
The perpendicular distance from Subnasale to Holdaway's H-line (upper lip Ls → soft chin Pog′) — how deep the base of the nose sits behind the lip line.
How
Draw the H-line Ls→Pog′; drop a perpendicular from Sn; read in mm (norm ≈ 5 mm, Sn behind the line → reported anterior-positive here).
Purpose
One of Holdaway's harmony checks: it grades upper-lip curl and depth of the subnasale region. Deviations flag a lip that is too taut/flat (small value) or an overly deep, protrusive lip curl (large value).
High
Above the norm reads as a deep subnasale recess behind a prominent lip (strong lip curl).
Low
Below the norm reads as a shallow recess — flat, strained upper lip against the nose base.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Subnasale to H-line here is a real reading and not a diagram.