Measurement · ANB
ANB angle
Loading the reference ceph.
Definition
The angle between the N–A and N–B lines (computed as SNA − SNB) — the sagittal discrepancy BETWEEN the two jaws. The single most-quoted skeletal classification number.
How
Draw N→A and N→B; ANB is the angle between them at Nasion. It is signed: positive when A point is ahead of B point (maxilla leads), negative when B point leads.
Purpose
Classifies the skeletal pattern: roughly 0–4° = Class I, above ~4° = Class II (maxilla ahead of mandible), negative/below ~0° = Class III. Because it is the difference of SNA and SNB it cancels cranial-base position — but it can still be biased by Nasion's vertical position and jaw rotations (which is why Wits is read alongside).
High
Above the norm reads as the maxilla sits ahead of the mandible — skeletal Class II relationship.
Low
Below the norm reads as the mandible sits ahead of the maxilla — skeletal Class III relationship.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so ANB angle here is a real reading and not a diagram.