Lower arch

The lower arch should be examined and planned in the first instance. Whatever treatment is carried out in the lower arch often determines the treatment to be carried out in the upper. Examine the teeth for any tipping, rotations and crowding. Teeth which are tipped mesially are much more amenable to treatment, both with removable and fixed appliances than teeth which are distally tipped. They also respond much better to extractions and spontaneous alignment than other teeth. The presence or absence of rotations is important because rotated teeth are most easily treated with fixed appliances. The more crowded the teeth are the more likely it is that extractions will be needed in order to correct the malocclusion. A method of assessing crowding is given in Figure 3. Firstly, measure the size of the teeth and add these together (length A). Then measure from the mid-line to the distal of the canine with a pair of dividers. Measure from the distal of the canine to the mesial of the first permanent

Fig. 1 Decalcification attributable to fixed appliances and a patient with poor oral hygiene throughout treatment

Fig. 2 This patient has a reasonable need for orthodontic treatment, but the poor oral hygiene and gingival condition precludes this

molar. Add these together to give you the approximate arch length (length B). Subtract B from A to give you the degree of crowding. This must be repeated for both sides of the arch.

The degree of crowing influences the need for extractions. Although one should not be dogmatic and several other factors influence the planning of extractions, as a general rule the greater the crowding the more likely extractions are necessary. Table 1 gives an outline of the relation between degree of crowding and need for extractions.

Table 1 Relationship between crowding and extractions

Degree of crowding

Need for extractions

< 5 mm


5-10 mm


> 10 mm


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