The British Standards classification defines a Class II division 1 incisor relationship as follows: ‘the lower incisor edges lie posterior to the cingulum plateau of the upper incisors, there is an increase in overjet and the upper central incisors are usually proclined’. In a Caucasian population the incidence of Class II division 1 incisor relationship is approximately 15–20 per cent.
Prominent upper incisors, particularly when the lips are incompetent, are at increased risk of being traumatized. It has been shown that children with an overjet greater than 9 mm are twice as likely to have suffered trauma involving their upper incisor teeth as are those with normal or reduced overjets.
9.1.1. Skeletal pattern
A Class II division 1 incisor relationship is usually associated with a Class II skeletal pattern, commonly due to a retrognathic mandible (Fig. 9.1). However, proclination of the upper incisors and/or retroclination of the lower incisors by a habit or the soft tissues can result in an increased overjet on a Class I (Fig. 9.2), or even a Class III skeletal pattern.
A Class II division 1 incisor relationship is found in association with a range of vertical skeletal patterns. Management of those patients with significantly increased or significantly reduced vertical proportions is usually difficult and is the province of the specialist.
9.1.2. Soft tissues
The influence of the soft tissues on a Class II division 1 malocclusion is mainly mediated by the skeletal pattern, both anteroposteriorly and vertically, and also by the patient’s efforts to achieve an anterior oral seal.
In a Class II division 1 malocclusion the lips are typically incompetent owing to the prominence of the upper incisors and/or the underlying skeletal pattern. If the lips are incompetent, the patient will try to achieve an anterior oral seal in one of the following ways:
circumoral muscular activity to achieve a lip-to-lip seal (Fig. 9.3);
the mandible is postured forwards to allow the lips to meet at rest;
the lower lip is drawn up behind the upper incisors (Fig. 9.4);
the tongue is placed forwards between the incisors to contact the lower lip, often contributing to the development of an incomplete overbite;
a combination of these.
Where the patient can achieve lip-to-lip contact by circumoral muscle activity or the mandible is postured forwards, the influence of the soft tissues is often to moderate the effect of the underlying skeletal pattern by dento-alveolar compensation. More commonly a seal is achieved by the lower lip being drawn up behind the upper incisors, which leads to retroclination of the lower labial segment and/or proclination of the upper incisors with the result that the incisor relationship is more severe than the underlying skeletal pattern.
However, if the tongue comes forward to contact the lower lip during swallowing, proclination of the lower incisors may occur, helping to compensate for the underlying skeletal pattern. This type of soft tissue behaviour is often associated with increased vertical skeletal proportions and/or grossly incompetent lips, or a habit which has resulted in an increase in overjet and an anterior open bite. In practice, it is often difficult to determine the degree to which this is adaptive tongue behaviour, or whether a rarer endogenous tongue thrust exists (see Chapter 12).
Infrequently, a Class II division 1 incisor relationship occurs owing to retroclination of the lower incisors by a very active lower lip (Fig. 9.5).
9.1.3. Dental factors
A Class II division 1 incisor relationship may occur in the presence of crowding or spacing. Where the arches are crowded, lack of space may result in the upper incisors being crowded out of the arch labially and thus to exacerbation of the overjet. Conversely, crowding of the lower labial segment may help to compensate for an increased overjet in the same manner. In such cases, extractions anterior to the second premolars in the lower arch may result in the lower labial segment dropping lingually with a concomitant worsening of the incisor relationship.
A persistent digit-sucking habit will act like an orthodontic force upon the teeth if indulged in for more than a few hours per day. The severity of the effects produced will depend upon the duration and the intensity, but the following are commonly associated with a determined habit (Fig. 9.6):
proclination of the upper incisors;
retroclination of the lower labial segment;
an incomplete overbite or a localized anterior open bite;
narrowing of the upper arch thought to be mediated by the tongue taking up a lower position in the mouth and the negative pressure generated during sucking of the digit.
The first two effects will contribute to an increase in overjet.
The effects of a habit will be superimposed upon the child’s existing skeletal pattern and incisor relationship, and thus can lead to an increased overjet in a child with a Class I or Class III skeletal pattern, or can exacerbate a pre-existing Class II malocclusion. The effects may be asymmetric if a single finger or thumb is sucked (Fig. 9.7).
9.2. OCCLUSAL FEATURES
The overjet is increased, and the upper incisors may be proclined, perhaps as the result of a habit or an adaptive swallow; or upright, with the increased overjet reflecting the skeletal pattern. The overbite is often increased, but may be incomplete as a result of an adaptive tongue-forward swallow, a habit, or increased vertical skeletal proportions. If the latter two factors are marked, an anterior open bite may result. If the lips are grossly incompetent and are habitually apart at rest, drying of the gingivae may lead to an exacerbation of any pre-existing gingivitis.
The molar relationship usually reflects the skeletal pattern unless early deciduous tooth loss has resulted in mesial drift of the first permanent molars.
9.3. ASSESSMENT OF, AND TREATMENT PLANNING IN, CLASS II DIVISION 1 MALOCCLUSIONS
Before deciding upon a definitive treatment plan the following factors should be considered:
The patient’s age
This is of importance in relation to facial growth: first whether further facial growth is to be expected, and second, if further growth is anticipated, whether this is likely to be favourable or unfavourable. In the ‘average’ growing child, forward growth of the mandible occurs during the pubertal growth spurt and the early teens. This is advantageous in the management of Class II malocclusions. However, correction of the incisor relationship in a child with increased vertical skeletal proportions and a backward-opening rotational pattern of growth has a poorer prognosis for stability. This is because the anteroposterior discrepancy will worsen with growth, and in addition an increase in the lower face height may reduce the likelihood of lip competence at the end of treatment.
In the adult patient, a lack of growth will reduce the range of skeletal Class II malocclusions that can be treated by orthodontic means alone and will also make overbite reduction more difficult.
The difficulty of treatment
The skeletal pattern is the major determinant of the difficulty of treatment. Those cases with a marked anteroposterior discrepancy and/or significantly increased or reduced vertical skeletal proportions will require careful evaluation, an experienced orthodontist, and possibly surgery for a successful result.
The results of a recent retrospective study of over 1200 consecutively treated Class II division 1 malocclusions found that patients with large overjets and more upright incisors were less likely to achieve an excellent outcome.
The likely stability of overjet reduction
The soft tissues are the major determinant of stability following overjet reduction. Before planning treatment it is often helpful to try to determine those factors that have contributed to the development of that particular Class II division 1 maloccusion and the degree to which they can be modified or corrected by treatment. For example, the patient shown in Fig. 9.8 has an increased overjet on a Class I skeletal pattern with a lower lip trap. In the absence of a habit, it is probable that the upper incisors were deflected labially as they erupted, and it is likely that
retraction of the upper incisors within the control of the lower lip would be stable as the lips would then be competent. In contrast, the patient shown in Fig. 9.9 has a Class II skeletal pattern with increased vertical skeletal proportions and markedly incompetent lips. An anterior oral seal was achieved by contact between the tongue and lower lip. In this case overjet reduction is unlikely to be stable as, following retraction, the upper labial segment would not be controlled by the lower lip and the forward tongue swallow would probably continue.
Ideally, at the end of overjet reduction the lower lip should act on the incisal one-third of the upper incisors and be able to achieve a competent lip seal. If this is not possible, it should be considered whether treatment is necessary and, if indicated, whether prolonged retention or even surgery is required.
The patient’s facial appearance
In some cases a consideration of the profile may help to make the decision between two alternative modes of treatment. For example, in a case with a Class II skeletal pattern due to a retrusive mandible, a functional appliance may be preferable to distal movement of the upper buccal segments with headgear. The profile may also influence the decision whether or not to relieve mild crowding by extractions.
Occasionally, although management by orthodontics alone is feasible, this will be to the detriment of the facial appearance and acceptance of the increased overjet or a surgical approach may be preferred. Features which may lead to this scenario include an obtuse nasolabial angle or excessive upper incisor show (Fig. 9.10).
9.3.1. Practical treatment planning
Treatment planning in general is discussed in Chapter 7. Class II division 1 malocclusions are commonly associated with increased overbite, which must be reduced before the overjet can be reduced. Overbite reduction requires space (about 1–2 mm for an averagely increased overbite) and allowance for this must be made when planning space requirements in the lower arch. Significantly increased overbites will require more space and fixed appliances, or even surgery. Overbite reduction is also considered in more detail in Chapter 10, Section 10.3.1.
If extractions are required in the lower arch, both spontaneous and active tooth movement are facilitated by removal of the corresponding tooth in the upper arch. The actual choice of extraction site will depend upon the presence of crowding, the tooth movements planned, and their anchorage requirements. However, in the treatment of moderately severe Class II division 1 malocclusions with fixed appliances, lower second premolars and upper first premolars may be chosen. This extraction pattern favours forward movement of the lower molar to aid correction of the molar relationship and retraction of the upper labial segment.
Where the lower arch is well aligned and the molar relationship is Class II, space for overjet reduction can be gained by distal movement of the upper buccal segments or by extractions. Where possible, a Class I buccal segment relationship is preferable. If extractions are carried out in the upper arch only, the molar relationship at the end of treatment will be Class II. This is functionally satisfactory, but as half a molar width is narrower than a premolar, some residual space often remains in the upper arch. If fixed appliances are used, the upper first molar can be rotated mesiopalatally to take up this space by virtue of its rhomboid shape.
Distal movement is discussed in more detail in Chapter 7, Section 7.7.3, and is usually considered if the molar relationship is half a unit Class II or less, although a full unit of space can be gained in a cooperative, growing patient. If the prognosis for overjet reduction is guarded, it may be advisable to gain space
in the upper arch by distal movement of the upper buccal segments rather than by extractions. Then should relapse occur this will not result in a reopening of the extraction space.
Treatment in the following situations is difficult and is best managed by a specialist:
The molar relationship is Class II and the lower arch is crowded as the extraction of one unit in each quadrant in the upper arch will not give sufficient space for relief of crowding and overjet reduction (see Fig. 7.14).
The molar relationship is greater than one unit Class II.
Management of these cases may involve the extraction of four teeth from the upper arch; distal movement of the upper buccal segments; or a functional appliance used initially to gain a degree of anteroposterior correction. Upper and lower fixed appliances are then usually required to complete alignment.
9.4. EARLY TREATMENT
Given the susceptibility of prominent incisors to trauma, early treatment is a tempting proposition. In addition, the child’s parents are often concerned and are keen for early treatment. However, there are a number of factors that need to be considered:
In younger children the lips are often incompetent, thus reducing the chances of stability following overjet reduction. Therefore, if treatment is carried out in the early mixed dentition, very prolonged retention may be required until the permanent dentition is established, with obvious implications for dental health.
Because of space considerations it may not be possible to reduce the overjet fully, thus increasing the chances of relapse.
If the upper incisors are retracted before the maxillary permanent canines have erupted, there is a risk of root resorption or deflection of the canines.
In practice, if overjet reduction is carried out in the early mixed dentition, further treatment is often required once the permanent dentition is established, by which time the patient’s co-operation is flagging.
In America a large, randomized, controlled clincial trial has been set up to look at the timing of treatment for Class II malocclusions. Pre-adolescent children were randomized to either observation or to early treatment with either a functional appliance or headgear. Following this phase patients in all three groups
underwent comprehensive treatment with fixed appliances in the permanent dentition. The preliminary data from this study indicates that the early skeletal effects from functional or headgear appliance treatment are not maintained long-term and that following completion of fixed appliance therapy in the permanent dentition, little difference, if any, remained between the early treatment and control (observation) groups. Although, on average, the time in fixed appliances was reduced for children who underwent early treatment the overall treatment time was considerably longer if the early treatment time was included.
Fig. 9.11. Boy aged 9 years with a Class II division 1 malocclusion on a Class II skeletal pattern. As the upper incisors were at risk of trauma, treatment was started early with a functional appliance. Following eruption of the permanent dentition, definitive treatment involving the extraction of all four second premolars and the use of fixed appliances was carried out to correct the inter-incisal angle and alieviate the crowding: (a)–(c) pretreatment (age 9); (d) at end of treatment with functional appliance (note the retroclination of the upper incisors as most of the reduction of the overjet has been achieved by dento-alveolar change); (e) following extraction of second premolars fixed appliances were placed; (f)–(h) following removal of fixed appliances (age 15).
At present many clinicians feel that treatment is best deferred until the eruption of the secondary dentition where space can be gained for relief of crowding and reduction of the overjet by the extraction of permanent teeth (if indicated), and soft tissue maturity increases the likelihood of lip competence. In the interim a custom-made mouthguard can be worn for sports. However, if the upper incisors are thought to be at particular risk of trauma during the mixed dentition, treatment with a functional appliance can be considered (Fig. 9.11).
9.5. MANAGEMENT OF AN INCREASED OVERJET ASSOCIATED WITH A CLASS I OR MILD CLASS II SKELETAL PATTERN
Fixed appliances, with extractions if indicated, will give good results in skilled hands in this group (Fig. 9.12).
Provided the skeletal pattern is Class I, that fixed appliances are not indicated for other features of the malocclusion, and that the increased overjet can be reduced by tilting of the upper labial segment, a removable appliance can be considered (Fig. 9.13). The feasibility of using tilting movements to reduce an overjet can be evaluated with a prognosis tracing from a lateral cephalometric radiograph (see Chapter 6, Section 6.8).
Fig. 9.13. Class II division 1 malocclusion managed with removable appliances. The patient suffered from recurrent ulceration due to cyclic neutropenia and therefore the patient’s medical practitioner requested an appliance which could be removed if the ulceration became severe: (a), (b) pretreatment; (c) showing removable appliance with palatal finger springs to retract the canines and a flat anterior bite plane for overbite reduction; (d) post-treatment.
If lower arch extractions are required, the likelihood that good spontaneous alignment of the lower arch will occur during treatment with an upper removable appliance is increased if moderate crowding is managed by extraction of the first premolars in a growing child. If the crowding is mild, consideration should be given to either accepting the crowding, perhaps with the extraction of second molars, or extracting the second premolars and using fixed appliances (see Chapter 7, Section 7.7).
A functional appliance can be used to reduce an overjet in a cooperative child with well-aligned arches and a mild to moderate skeletal Class II pattern, provided that treatment is timed for the pubertal growth spurt (Chapter 18). If the arches are crowded, anteroposterior correction can be achieved with a functional appliance followed by extractions, and then fixed appliances can be used to achieve alignment and to detail the occlusion.
9.6. MANAGEMENT OF AN INCREASED OVERJET ASSOCIATED WITH A MODERATE TO SEVERE CLASS II SKELETAL PATTERN
Management of the more severe case is the province of the experienced operator. There are three possible approaches to treatment:
Growth modification by attempting restraint of maxillary growth, by encouraging mandibular growth, or by a combination of the two (Fig. 9.14). In practice, the amount of change that can be produced is small and success is dependent upon favourable growth and an enthusiastic patient. Prolonged retention until growth is complete is desirable. Headgear can be used to try and restrain growth of the maxilla horizontally and/or vertically, depending upon the direction of force relative to the maxilla. Functional appliances
appear to produce restraint of maxillary growth whilst encouraging mandibular growth.
Orthodontic camouflage using fixed appliances to achieve bodily retraction of the upper incisors (Fig. 9.15). The severity of the case that can be approached in this way is limited by the availability of cortical bone palatal to the upper incisors and by the patient’s facial profile. If headgear is used in conjunction with this approach, a degree of growth modification may also be produced in favourably growing children.
Surgical correction (see Chapter 20).
Fig. 9.14. Patient treated by growth modification. Because correction required a combination of restraint of vertical and forward growth of the maxilla and encouragement of forward growth of the mandible, a functional appliance with high-pull headgear was used: (a), (b) pretreatment aged 12 years; (c), (d) at the end of retention aged 15 years.
As mandibular growth predominates over maxillary growth during the pubertal growth spurt, more Class II malocclusions than Class III malocclusions can be managed with orthodontics alone. Research indicates that the amount of growth modification that can be achieved is limited, but even a small amount of skeletal change can be helpful. In practice, the child with a moderately severe Class II skeletal pattern can often be managed by a combination of approaches 1 and 2, provided that growth is not unfavourable. This usually involves an initial phase of functional appliance therapy carried out during the pubertal growth spurt, followed by a second phase of fixed appliance treatment plus extractions if indicated.
Orthodontic camouflage can also be achieved by proclination of the lower labial segment. In the main this movement is inherently instable, but it can be stable in a small number of cases where the lower incisors have been trapped lingually by an increased overbite or pushed lingually by a habit or by a lower lip
trap. Diagnosis of these cases is difficult and the inexperienced operator should avoid proclination of the lower labial segment at all costs. Occasionally, some proclination of the lower labial segment and permanent retention is felt by the adult patient and operator to be preferable to a surgical option.
Unfortunately, gummy smiles associated with increased vertical skeletal proportions and/or a short upper lip will often worsen as the incisors are retracted. Therefore active steps should be taken to manage this problem. Milder cases are best managed by either the use of high-pull headgear to a functional type of appliance or a fixed appliance to try and restrain maxillary vertical development while the rest of the face grows. In severe cases of vertical maxillary excess or where there is an excessive amount of upper incisor show in an adult patient, surgery to impact the maxilla is advisable.
In cases with a severe Class II skeletal pattern, particularly where the lower facial height is significantly increased or reduced, a combination of orthodontics and surgery may be required to produce an aesthetic and stable correction of the malocclusion (see Chapter 20). The threshold for surgery is lower in adults because of a lack of growth.
Fig. 9.15. Patient with Class II division 1 malocclusion on a moderately severe Class II skeletal pattern treated by orthodontic camouflage in which both upper first premolars were extracted to gain space for overjet reduction and fixed appliances were used for bodily retraction of the upper incisors: (a)–(c) pretreatment (note the upright upper incisors); (d)–(f) post-retention.
A common mistake is to stop treatment before overjet reduction is fully completed. In many cases the patient continues to retract the lower lip behind the
upper incisors to achieve an anterior oral seal, with a subsequent relapse in incisor position. Therefore full reduction of the overjet and the achievement of lip competence is advisable.
Unfortunately no amount of retention will make an inherently unstable tooth position become stable, and so retention must be considered during treatment planning. Provided that the upper incisors have been retracted to a position of soft tissue balance and are controlled by the lower lip, only a short period of retention is required to allow for adaptation of the periodontal fibres and soft tissues. One exception to this is functional appliance therapy where retention until growth is complete is advisable (Chapter 18).
PRINCIPAL SOURCES AND FURTHER READING
Aelbers, C. M. F and Dermaut, L. R. (1996). Orthopedics in orthodontics: fiction or reality. A review of the literature. American Journal of Orthodontics and Dentofacial Orthopedics, 110, 513–19 and 667–71.
Banks, P. A. (1986). An analysis of complete and incomplete overbite in Class II division 1 malocclusions (an analysis of overbite incompleteness). British Journal of Orthodontics, 13, 23–32.
Battagel, J. M. (1989). Profile changes in Class II division 1 malocclusions: a comparison of the effects of Edgewise and Frankel appliance therapy. European Journal of Orthodontics, 11, 243–53.
Burden D. J. et al. (1999). Predictors of outcome among patients with Class II division 1 malocclusion treated with fixed appliances in the permanent dentition. American Journal of Orthodontics and Dentofacial Orthopedics, 116, 452–59.
King, G. J., Keeling, S. D., Hocevar, R. A., and Wheeler, T. T. (1990). The timing of treatment for Class II malocclusions in children: a literature review. Angle Orthodontist, 60, 87–97.
The arguments for and against early treatment of Class II division 1 malocclusions.
Tulloch, C. J. F., Phillips, C., and Proffit, W. R. (1998). Benefit of early Class II treatment: progress report of a two-phase randomised clinical trial. American Journal of Orthodontics and Dentofacial Orthopedics, 113, 62–72.
The results of this important trial are essential reading for any clinician involved in treating patients with Class II malocclusions.