Measurement · INTER
Interincisal angle
Loading the reference ceph.
Definition
The posterior angle between the long axes of the most prominent upper and lower central incisors — how the incisors 'lean into' each other.
How
Draw the upper incisor long axis (apex U1A → tip U1T) and the lower incisor long axis (L1A → L1T); the interincisal angle is the angle between the two axes on the lingual (posterior) side, where they cross behind the incisal tips.
Purpose
Summarizes total incisor procumbency in one number. Proclined (flared) incisors close the angle; upright or retroclined incisors open it. A very obtuse angle with a deep bite is the classic Class II division 2 pattern; a low angle means dental protrusion with lip strain risk on retraction.
High
Above the norm reads as upright/retroclined incisors (large, obtuse angle) — think Class II div 2, deep-bite tendency.
Low
Below the norm reads as proclined, flared incisors (bimaxillary dental protrusion) — lips and profile are being pushed forward by the teeth.
Built from
Listed by Steiner, Downs.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Interincisal angle here is a real reading and not a diagram.