Class II and Class III Subdivisionsthe subdivision always refers to the Class II side for Class II subdivisions and the Class III

side for Class III subdivisions. It is true dental asymmetry not related to localised crowding

Types of Class II SubdivisionsJanson et al 2003 described two basic types.

1. A Type 1 Class II subdivision malocclusion demonstrates coincidence of the maxillary dental

midline with the facial midline and deviation of the mandibular midline.

Any treatment in these Type 1 cases should therefore be aimed at the mandibular arch. This

also maintains symmetry in the maxillary arch, where it is most visible to the patient.

A. For cases with moderate to severe crowding, incisor protrusion, and/or the absence of a

passive lip seal, an extraction approach is ideal. But should three or four premolars be

extracted? To answer this question, Janson 2003 retrospectively evaluated 51 patients with

Class II subdivision malocclusions. Twenty-eight of the patients had four symmetric

premolars removed, while the remaining 23 patients had three premolars removed, two in the

maxillary arch and one in the mandibular arch on the Class I side. The results showed no real

difference for most of the variables assessed. However, the three premolar extraction group

had a greater improvement of the initial interdental midline deviation.

B. Cases with mild crowding are treated with single unit extraction in the lower arch or molar

distalisation

2. A Type 2 Class II subdivision malocclusion has the opposite characteristics, demonstrating

coincidence of the mandibular dental midline with the facial midline and deviation of the

maxillary midline.

If extraction is indicated in these cases, then one maxillary premolar may be removed

Care must be taken to avoid tilting the teeth, skewing the arch, or overcorrecting the midline

of the highly visible maxillary anterior dentition.

The amount of crowding and midline discrepancy also influence the decision to extract a first

or second premolar.

3. Combination Class II subdivision treatment: The remaining 20% of cases show traits of both

Type 1 and Type 2 Class II subdivision malocclusion, with some discrepancy present in both

arches. The goal is therefore to aim correction at both arches, so interarch mechanics such as

elastics or a spring Class II corrector seem most appropriate

Early intervention

Some asymmetries may develop because of the early loss of teeth, and this could simply

involve space maintenance therapy to regain space or symmetry followed by space

maintenance.

Another possible cause is a single-or multiple-tooth crossbite, which results in a slide shift

upon occluding. Treatment entails correction of the cross-bite to remove the occlusal

interference that causes the slide shift upon closure

Types of Class III Subdivisions Although studies similar to those for Class II subdivisions have not been conducted in dental

Class III subdivision cases, Janson 2009 has suggested that an analogous rationale in

diagnosis and treatment planning can be applied in these patients.

Another option that could be considered in Class III subdivision cases is the extraction of a

mandibular incisor