Assessment of crowding. These photographs show the method of assessing the degree of crowding by
measuring the width of the misaligned tooth compared with the amount of available space in the arch. In this
example, the first photograph shows that the width of the tooth is 6 mm and the second photograph shows that
the amount of space available in the arch for this tooth is 4 mm. This suggests crowding of 2 mm for this tooth.
Incisor anteroposterior change
It is often necessary to alter the anteroposterior position of the upper incisors, particularly when reducing
an overjet. If incisors are retracted, this requires space; if incisors are proclined then space is created.
The aim is to create an overjet of 2 mm at the end of treatment. Every millimetre of incisor retraction
requires 2 mm of space in the dental arch. Conversely, for every millimetre of incisor proclination 2 mm
of space are created in the arch.
For example, if a patient presented with an overjet of 6 mm and the incisors needed to be retracted to
create a normal overjet of 2 mm, then this would require space. Every millimetre of retraction requires
2 mm of space. So to reduce the overjet by 4 mm would require 8 mm of space.
Levelling occlusal curves
Where there is no occlusal stop the lower incisors may over-erupt. This may result in an occlusal curve
which runs from the molars to the incisors and is known as a Curve of Spee as seen in Figure 2. The
amount of space required to level an increased curve of Spee is controversial, as it is affected by a number
of factors, such as the shape of the archform and tooth shape. However, as a guide Table 1 gives an
estimation of the space required.