Class II division 2 malocclusion
Class II division 2 is the term used to describe a malocclusion where the lower incisal edges occlude posterior to the cingulum plateau of the upper incisors and the upper central incisors are retroclined (British Standards Institute classification). The overbite (OB) is characteristically deep, the overjet maybe normal or increased, and the molar relationship is Class II. There is an association between this malocclusion and impacted maxillary canines. The prevalence of Class II division 2 is estimated to be approximately 10% among Caucasians. This malocclusion has a strong genetic association.
Aetiology of Class II division 2 malocclusion
Class II division 2 is commonly associated with a mild skeletal II pattern due to mandibular retrognathia. The chin point may be well positioned in a number of cases with retrusion more evident at the dento-alveolar region (Figure 23.1Ai). A moderate/severe skeletal II pattern may be present, however, is more likely to be associated with a Class II division 1 incisor relationship as the lips are more likely to be incompetent. Class II division 2 may rarely be associated with a skeletal I or III relationship if the soft tissue pattern is unfavourable.
Vertically, the lower anterior face height (LAFH) and Frankfort-Mandibular planes angle is often reduced (Figure 23.1Ai). This maybe associated with an anticlockwise (forward) mandibular growth rotation (see Chapter 5). A reduction in the LAFH predisposes to a high lower lip line, deep OB and a pronounced labiomental fold.
In the transverse dimension, there may be a scissor bite in the premolar region which is a result of narrowing of the lower arch and because a wider part of the maxilla opposes a narrower part of the mandible (relative transverse discrepancy, Chapter 8).
Soft tissue factors
As a result of the reduced LAFH, the lower lip usually rests high on the crowns of the maxillary central incisors (Figure 23.1Aii). A high lower lip line results in retroclination of the maxillary central incisors, an increase in interincisal angle and deepening of the OB (Figure 23.1Aiii).
A deep labiomental fold