Measurement · ACB
Anterior cranial base length (S–N)
Loading the reference ceph.
Definition
The linear length of the anterior cranial base, from Sella (center of the sella turcica) to Nasion.
How
Measure the straight-line distance S→N in mm.
Purpose
Scales the face: cranial-base length correlates with overall facial size, and S–N is the reference limb of SNA/SNB — an unusually short or long S–N warns you those angles may read biased. Also a component of the Björk–Jarabak linear set.
High
Above the norm reads as a long anterior cranial base (large cranial scaffold; angular measures to S–N read slightly smaller).
Low
Below the norm reads as a short anterior cranial base (angular measures to S–N read slightly larger; check ANB against Wits).
Built from
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Anterior cranial base length (S–N) here is a real reading and not a diagram.