OPTION 2

Incisor Anteroposterior Position:

•            This requires cephalometric assessment. The treatment objective at the outset will determine whether the existing lower incisor position is acceptable.

•            If a forward movement of the lower incisors is desired, for example in a Class II division 2 malocclusion, space will be created by this movement.

 

•            If all four lower incisors are advanced by 1 mm, additional space will be created distal of the incisors by an equivalent amount on each side, totalling 2 mm space.

•            Conversely, retraction of either the upper or lower incisors is a space requirement; a 1 mm retraction of all four incisors will require 2 mm space.

 

•            It is essential that the incisors which are measured cephalometrically are the same incisors which are used for measurement of the overjet and for the assessment of the crowding or spacing when deciding on the arch form.

•            The retraction of incisors by a distance requires the same amount of space in each buccal segment. In the lower diagram, the inter-molar distance is equivalent to the distance between second premolars in the upper diagram.

 

Retraction of incisors by a distance requires the same amount of space in each buccal segment

 

Key Concept

Incisor anteroposterior movement

•            With few exceptions, the lower incisor anteroposterior (AP) position should be accepted to maximise stability. In Class II malocclusions, the upper incisors must be retracted for overjet reduction. Conversely, in Class III malocclusions the upper incisors may be advanced and the lowers retracted to correct a reverse overjet.

•            For every 1 mm all four incisors are retracted, 2 mm of space (1 mm per quadrant) is required. Conversely, for every 1 mm all four incisors are advanced, 2 mm of space will be created.