INTRODUCTION

The British Standards Classification defines Class II division 2 malocclusion as follows: the lower incisor edges occlude posterior to the cingulum plateau of the upper incisors; the upper central incisors are retroclined, the overjet is usually minimal but may be increased. Among Caucasians, the prevalence is reported to be about 10%.¹

AETIOLOGY

This malocclusion has a strong genetic component² with most resulting from the interplay of skeletal and soft tissue factors.

Skeletal Factors

Usually the skeletal pattern is mildly Class II, due to mandibular retrognathia, but it may be Class I or even mildly Class III.^3,4 A reduced lower facial height is typical,⁵ in association with an anterior (anticlockwise) mandibular growth rotation, which tends to increase the overbite and lead to forward projection of the chin^2,5 (Figure 17.1a). Due to the relatively wide maxillary base, and narrower lower intercanine width,⁶ the first premolars may be in lingual crossbite (scissors bite).

Figure 17.1 (a) Class II skeletal pattern with reduced FMPA, deep labiomental fold and relatively prominent chin point; (b) associated high lower lip line evident on smiling; and (c) typical Class II division 2 malocclusion.

Soft Tissue Factors

As the lower facial height is reduced, the lower lip line is high on the upper incisors, covering more that one-third of the labial surface, and is the predominant cause of their retroclination⁷ (Figure 17.1b). Increased resting lower lip pressure (∼2.5 times as high as the upper lip resting pressure) is a complementary factor.⁸ Upper and lower lips are also thicker compared with Class 1 malocclusion.⁹ Depending on the lower lip level, the relatively shorter maxillary lateral incisor crowns may either be retroclined along with the central incisors or escape lower lip control and be of average inclination but mesiolabially rotated, a manifestation of inherent crowding (Figure 17.1c). The reduced lower facial height also leads to a relative soft tissue excess of the lower lip, reflected in the commonly observed deep labio-mental fold. Where the lips are strap-like regardless of the skeletal pattern, the upper and lower incisors may be retroclined (bimaxillary retroclination; Figure 17.2); this is sometimes associated with a gummy smile and may be aggravated by upper incisor overeruption.

Figure 17.2 Bimaxillary retroclination; peg-shaped lateral incisor; retained primary canine (the permanent canine was palatally displaced).

Dental Factors

The cingulum on the upper incisors may be reduced or absent, thereby allowing overeruption of the lower incisors to increase the interincisal angle and deepen the overbite.¹⁰ The latter may be exacerbated by a Class II skeletal pattern and retroclination of upper and lower incisors. Relative to other malocclusion types, a more acute upper incisor crown–root angulation¹⁰ and smaller mesiodistal width of the upper and lower incisors have been identified.² There is also a higher incidence of palatally impacted maxillary canines¹¹ and of peg-shaped or absent maxillary lateral incisors¹² (Figure 17.2). Retroclination of the upper incisors, and possibly of the lower incisors, worsens pre-existing crowding.

TREATMENT PLANNING

The factors which should be considered, in particular, with regard to treatment planning are given in Table 17.1. Two principal decisions have to be made with regard to treatment in relation to the incisor relationship and crowding: to accept or correct the incisor relationship; to extract or not for relief of crowding and incisor alignment.

Table 17.1 Factors to consider in treatment planning of Class II division 2 malocclusions