Inter-incisor gap (II gap): With the mouth open maximally, measure the distance between the incisors (or alveolar margins). The inter-incisor gap is affected by temporo-mandibular joint and upper cervical spine mobility.

If the gap is less than 3 cm, intubation difficulty is more likely. If the gap is less than 2.5 cm LMA insertion will also be difficult.

In a large series, an II gap of less than 3 cm reduced easy intubation from 95 % to 62 %.