10.2. OCCLUSAL FEATURES
Classically, the upper central incisors are retroclined and the lateral incisors are at an average angulation or are proclined, depending upon their position relative to the lower lip (see Fig. 10.4). Where the lower lip line is very high the lateral incisors may be retroclined (see Fig. 10.3). The more severe malocclusions occur either where the underlying skeletal pattern is more Class II or where the lip musculature is active, causing bimaxillary retroclination.
In mild cases the lower incisors occlude with the upper incisors, but in patients with a more severe Class II skeletal pattern the overbite may be complete onto the palatal mucosa. In a small proportion of cases the lower incisors may cause ulceration of the palatal tissues (Fig. 10.7), and in some patients retroclination of the upper incisors leads to stripping of the labial gingivae of the lower incisors (Fig. 10.8). In these cases the overbite is described as traumatic, but fortunately both are comparatively rare.
In the mild Class II division 2 malocclusion, where the lower incisors occlude with the upper incisors, treatment can be limited to achievement of alignment and the incisor relationship accepted.
Stable correction of a Class II division 2 incisor relationship is difficult as it requires not only reduction of the increased overbite (discussed in Section 10.3.1), but also reduction of the inter-incisal angle which classically is increased (Fig. 10.10). If re-eruption of the incisors and therefore an increase in overbite is to be resisted, the inter-incisal angle needs to be reduced, preferably to between 125° and 135°, so that an effective occlusal stop is created (Fig. 10.11).
The inter-incisal angle in a Class II division 2 malocclusion can be reduced in a number of ways:
Torquing the incisor roots palatally/lingually with a fixed appliance (Fig. 10.12).
Proclination of the lower labial segment (Fig. 10.13). This approach should only be employed by the experienced as, although it provides additional space for alignment of the lower incisor teeth, proclination of the lower labial segment will only be stable if it has been trapped lingually by the upper labial segment.
Proclination of the upper labial segment followed by use of a functional appliance to reduce the resultant overjet and achieve intermaxillary correction (Fig. 10.14).
A combination of the above approaches.
The treatment approach chosen for a particular patient will depend upon the aetiology of the malocclusion, the presence and degree of crowding, the patient’s profile, and their probable compliance.
Once the decision has been made to accept or correct the incisor relationship, consideration should be given as to whether extractions are required to relieve crowding and to provide space for incisor alignment. Some practitioners have
argued that closure of excess extraction space in a Class II division 2 malocclusion will result in further retroclination of the labial segments and a ‘dished-in profile’. This claim is usually made in association with the presentation of isolated case reports. However, research using groups of carefully matched patients has shown that there is little difference in the amount of retraction of the lips between extraction and non-extraction treatment approaches (see Chapter 7, Section 7.8). Nevertheless, it would seem advisable in the management of Class II division 2 malocclusions to minimize lingual movement of the lower incisors in order to avoid any possibility of worsening the patient’s overbite; indeed, it may be preferable to accept a degree of lower arch crowding rather than run this risk. Certainly, extraction of permanent teeth in the lower arch in Class II division 2 maloccclusions should be approached with caution, and if any doubt exists specialist advice should be sought. In addition, clinical experience suggests that space closure occurs less readily in patients with reduced vertical skeletal proportions, which are commonly associated with Class II division 2 malocclusions, than in those with increased lower face heights.
In general, proclination of the lower labial segment should be considered unstable, but it has been argued that in some Class II division 2 malocclusions the lower labial segment is trapped behind the upper labial segment, resulting in retroclination of the lower incisors and constriction of the lower intercanine width. This means that a limited increase in intercanine width and a degree of proclination of the lower labial segment can be stable, although it is important to assess the lower labial supporting tissues to avoid iatrogenic gingival recession. However, proclination of the lower incisors is helpful in reducing both overbite and the inter-incisal angle.
In view of the above comments, it is not surprising that Class II division 2 malocclusions are managed more frequently on a non-extraction basis, particularly in the lower arch, than are other types of malocclusion.
This discussion has highlighted some of the difficulties inherent in planning treatment of Class II division 2 incisor relationships. Except for the mild case, where management is to be limited to alignment of the upper arch, correction of Class II division 2 incisor relationships is best left to the specialist.
10.3.1. Approaches to the reduction of overbite
Intrusion of the incisors
Actual intrusion of the incisors is difficult to achieve. Fixed appliances are necessary and the mechanics employed pit intrusion of the incisors against extrusion of the buccal segment teeth; as it is easier to move the molars occlusally than to intrude the incisors into bone, the former tends to predominate. In practice, the effects achieved are relative intrusion, where the incisors are held still while vertical growth of the face occurs around them, plus extrusion of the molars. High-pull headgear can be hooked onto the anterior segment of the archwire of an upper fixed appliance to try and achieve intrusion of the upper labial segment; however, this approach has become less popular due to concerns over headgear safety and root resorption.
Increasing the anchorage unit posteriorly by including second permanent molars (or even third molars in adults) will aid intrusion of the incisors and help to limit extrusion of the molars. Arches which bypass the canines and premolars to pit the incisors against the molars, for example the utility arch (Fig. 10.15), are employed with some success to reduce overbite by intrusion of the incisors, although some molar extrusion does occur.
Eruption of the molars
Use of a flat anterior bite-plane on an upper removable appliance to free the occlusion of the buccal segment teeth will, if worn conscientiously, limit further occlusal movement of the incisors and allow the lower molars to erupt, thus reducing the overbite. This method requires a growing patient to accommodate the increase in vertical dimension that results, otherwise the molars will reintrude under the forces of occlusion once the appliance is withdrawn. However, this tendency can be resisted to a degree if the treatment creates a stable incisor relationship.
Extrusion of the molars
As mentioned above, the major effect of attempting intrusion of the incisors is often extrusion of the molars. This may be advantageous in Class II division 2 cases as this type of malocclusion is usually associated with reduced vertical proportions. Again, vertical growth is required if the overbite reduction achieved in this way is to be stable.
Proclination of the lower incisors
Advancement of the lower labial segment anteriorly will result in a reduction of overbite as the incisors tip labially. This approach should only be carried out by the experienced orthodontist (see Section 10.3.2). However, in a few cases where the lower incisors have been trapped behind the upper labial segment by an increased overbite, fitting of an upper bite-plane appliance may allow the lower labial segment to procline spontaneously (Fig. 10.16).
In adults with a markedly increased overbite and those patients where the underlying skeletal pattern is more markedly Class II, a combination of orthodontics and surgery is required.
10.3.2. Practical management
The incisor relationship is to be accepted
In milder cases where the lower incisors occlude onto tooth tissue it may be possible to accept the increased overbite, limiting treatment to alignment, particularly of the upper lateral incisors.
As discussed above, it may be preferable to accept mild to moderate lower arch crowding rather than run the risk of extractions leading to lingual movement of the lower labial segment and a worsening of the overbite. If the crowding is marked, extraction of lower first premolars may be required. However, if lower arch extractions run the risk that the lower incisors may tilt lingually and come to occlude with the palatal gingivae behind the upper incisors, it may be preferable to use fixed appliances and correct the incisor relationship instead (see below).
Space for alignment of the upper arch can be created by extractions (Chapter 7, Section 7.7.1) or by distal movement of the upper buccal segment teeth (Chapter 7, Section 7.7.3). Extraction of the upper first premolars is usually indicated if the first premolars have been lost in the lower arch or the buccal segment relationship is greater than half a unit Class II. Extraction of second premolars will give less space anteriorly and can be considered if upper arch crowding is mild and/or
distal movement of the molars is not indicated or the patient is unwilling to wear headgear.
Distal movement of the upper buccal segments can be considered where the lower arch alignment is to be accepted and the molar relationship is not greater than half a unit Class II. Extraction of the upper second molars may be required to facilitate distal movement, provided that upper third molars of a good size are present and in a favourable position. In some cases removable appliances can be used to achieve upper arch alignment. Although a removable appliance cannot be used to de-rotate rotated upper lateral incisors, relief of crowding and retraction of these teeth into the line of the arch may provide sufficient improvement (Fig. 10.17). The appliance should incorporate a flat anterior bite-plane to free the occlusion of the lower labial segment and achieve some overbite reduction.
When planning treatment in these cases it is important to bear in mind that, if the upper incisors are retroclined, the upper canines should only be retracted sufficiently to provide space for alignment of the incisors. This is because retroclined upper incisors occupy less arch length than upright incisors; therefore if the maxillary canines are retracted to Class I, excess space will be created in the upper labial segment. This may leave the upper canines buccally positioned relative to the arch in a half-unit Class II relationship with the lower canines, in which case consideration should be given to correcting the incisor relationship with fixed appliances.
If use of a removable appliance will not produce an acceptable result then fixed appliances are indicated.
The incisor relationship is to be corrected
Correction of the incisor relationship is indicated where the overbite is complete to the palatal soft tissues, or is liable to become so following extractions in the lower arch to relieve crowding. In some patients, reduction of overbite is necessary in order to be able to treat other features of a malocclusion. Certainly, correction of the incisor relationship should be given priority if the overbite is traumatic.
It will be apparent from the discussion at the beginning of Section 10.3 that there are three possible treatment modalities as described below.
When fixed appliances are used the inter-incisal angle can be reduced by palatal/lingual root torque or by proclination of the lower incisors. The relative role of these two approaches in the management of a particular malocclusion is a matter of fine judgement.
Torquing of incisor apices is dependent upon the presence of sufficient cortical bone palatally/lingually and places a considerable strain on anchorage. This type of movement is also more likely to result in resorption of the root apices than other types of tooth movement.
Mild crowding in the lower arch may be eliminated by forward movement of the lower labial segment. If crowding is marked, extractions will be required and a lower fixed appliance used to ensure that space closure occurs without movement of the lower incisor edges lingually (Fig. 10.18). Space for correction of the incisor relationship can be gained by upper arch extractions or by distal movement of the upper buccal segments. If headgear is used for anchorage or distal movement, a direction of pull below the occlusal plane (cervical pull) is usually indicated in Class II division 2 malocclusions as the vertical facial proportions are reduced. A lingual crossbite, if present, usually affects the first premolars only. If extraction of the upper first premolars is not indicated, or if the second premolars
are involved, elimination of the crossbite will involve a combination of contraction across the affected upper teeth and expansion of the lower premolar width. Following treatment, the prognosis for the corrected position is good as cuspal interlock will help to prevent relapse.
On completion of treatment it is prudent to retain with a upper removable appliance incorporating a bite-plane. Ideally, retention should be continued until growth is complete to try and prevent a return of the overbite. Whilst this is not always practicable, one approach is to retain for about 6 months full time, followed by 6 months nights only. If proclination of the lower labial segment is decided upon, an assessment of the stability of this movement needs to be made at the planning stage and permanent retention instituted where indicated.
Functional appliances can be utilized in the correction of Class II division 2 malocclusions in growing patients with a mild to moderate Class II skeletal pattern and a relatively well-aligned lower arch (Fig. 10.19). Reduction of the inter-incisal angle is achieved mainly by proclination of the upper incisors, although some proclination of the lower labial segment may occur as a result of the functional appliance. If an activator type of functional appliance is used, then a pre-functional phase is required to procline any retroclined incisors and to expand the upper arch (to ensure the correct buccolingual arch relationship at the end of treatment). This can be achieved using a removable appliance (Fig. 10.20); this design is known as an ELSAA (Expansion and Labial Segment Alignment Appliance). If a twin-block functional is used, then a spring to procline the
incisors can be incorporated into the upper appliance. Finally, fixed appliances are often required to detail the occlusion. If the lower incisors have been proclined, the stability of their position should be assessed and, if doubtful, permanent retention (or at least retention until growth is complete) should be instituted.
Surgery (see Chapter 20)
A stable aesthetic orthodontic correction may not be possible in patients with an unfavourable skeletal pattern anteroposteriorly and/or vertically, particularly if growth is complete (Fig. 10.21). In these cases surgery may be necessary. A phase of presurgical orthodontics is required to align the teeth. However, arch levelling is usually not completed as extrusion of the molars is much more easily accomplished after surgery. Where the overbite is particularly marked, the lower labial segment may have to be set down surgically, in which case space will have to be created distal to the lower canines for the surgical cuts to be made.
PRINCIPAL SOURCES AND FURTHER READING
Burstone, C. R. (1977) Deep overbite correction by intrusion. American Journal of Orthodontics, 72, 1–22.
A useful paper for the more experienced orthodontist using fixed appliances.
Lee, R. T. (1999). Arch width and form: a review. American Journal of Orthodontics and Dentofacial Orthopedics, 115, 305–13.
Leighton, B. C. and Adams, C. P. (1986). Incisor inclination in Class II division 2 malocclusions. European Journal of Orthodontics, 8, 98–105.
Kim, T. W. and Little, R. M. (1999). Post retention assessment of deep overbite correction in Class II division 2 malocclusion. Angle Orthodontist. 69, 175–86.
Rutter, R. R. and Witt, E. (1990). Correction of Class II division 2 malocclusions through the use of the Bionator appliance. Report of two cases. American Journal of Orthodontics and Dentofacial Orthopedics, 97, 106–12.
Selwyn-Barnett, B. J. (1991). Rationale of treatment for Class II division 2 malocclusion. British Journal of Orthodontics, 18, 173–81.
This paper contains a carefully constructed argument for management of Class II division 2 malocclusion by proclination of the lower labial segment rather than extractions, in order to avoid detrimental effects upon the profile.
Selwyn-Barnett, B. J. (1996). Class II division 2 malocclusion: a method of planning and treatment. British Journal of Orthodontics, 23, 29–36.