Strategies for Treatment of Adolescent Patients with Class II Malocclusions
Urban Hägg, Ricky Wing Kit Wong
A German anatomist named Wilhem Roux (1850–1924) was the first to investigate the influence of natural forces and functional stimulation on form, and his work became the foundation for the principles of functional orthodontic appliances.1 In 1889 Roux asked, “How many thousands of children afflicted with jaw-borne deformities have had to tolerate useless appliances … before the infinite number of failures tend to deepening knowledge?”2
This question is still relevant today. We ask: Are there orthodontic devices currently in use that can deliver predictable and positive outcomes in the treatment of jaw-borne deformities such as skeletal Class II malocclusion? To answer this question, several randomized clinical trials (RCTs) have been conducted in recent years to study mixed dentition patients with Class II characteristics. In these studies subjects were divided into two groups: one group underwent early-stage (Phase 1) treatment using growth modification devices and the other group was the control group. Later, the patients in both groups underwent a phase of fixed appliance treatment, with and without extractions (this was Phase 2 for those who had had the Phase 1 treatment). By comparing the changes observed in patients during the Phase 1 treatment with the growth changes observed in the control group, one could estimate the effects of the treatment and also make comparisons between the groups treated with various “growth modificators.” No matched controls were available to estimate the treatment effects of the group undergoing fixed appliance therapy because it was considered unethical to delay treatment any further. Consequently it was at best possible to estimate and compare the treatment effects during the early phase; that is, to compare the treatment changes in the groups that had observation followed by a fixed appliance phase with the group that had a combination of growth modification and a fixed appliance. It was reported that in the groups that had undergone the Phase 1 treatment with growth modification devices, there was some effect on the sagittal jaw–base relationship with restraint, forward growth of the maxilla, and/or enhanced growth of the mandible.3,4 However, the possible advantage of these effects did not remain after the treatment with a fixed appliance when compared to the group that had fixed appliance only.
One study concluded that there were “remarkably similar outcomes with and without early phase 1 treatment,”5 while another study reported “an inferior final occlusal result” with the two-stage approach.6 A recent meta-analysis7 concluded that the “effectiveness of functional appliances on mandibular growth in the short term … provided in early adolescence … probably was not very clinically significant.” In conclusion, based on the reports from recent RCTs it seems that a number of orthodontic devices and concepts aimed at treating jaw discrepancies in the last century have had minimal to no benefit when used early.
Dentofacial Characteristics of Class II Malocclusion
Definition of Class II Malocclusion
The original definition of Class II malocclusion by Angle8 was based on the sagittal dental arch relationship of the permanent dentition based primarily on the original position of the first permanent molars. Class II malocclusion as defined by Angle had a bilateral distal molar relationship and, based on the position of the maxillary incisors, was divided into two divisions: Division 1 and Division 2, with proclined and retroclined maxillary incisors, respectively. Cases with a unilateral distal molar relationship were classified as Class II (Division 1 or 2) subdivision. This definition, still widely used, is limited to the sagittal dental arch relationship only, not taking into account the vertical and transversal dental arch relationships or the jaw-base relationship. Consequently, the original definition of Angle Class II malocclusion comprises subjects with a very wide range of dentofacial features, which have to be recognized in the orthodontic diagnosis and problem lists, treatment objectives, and treatment plans. Class II malocclusion is common in all ethnic groups and is reported as present in 10% to 25% of the general population.9
Differential Diagnosis of Class II Malocclusion
The distal relationship between the first permanent molars could be due to mesial rotation of the maxillary first permanent molars, maxillary dentoalveolar protrusion, a skeletal Class II jaw relationship, or a combination of all of these factors. Giuntini et al.10 reported that 80% of subjects with a Class II molar relationship had mesially rotated first maxillary molars. Based on conventional cephalometric analysis the average dentofacial pattern in subjects with Angle Class II malocclusion is skeletal Class II (increased A point nasion B point [ANB] angle) usually with a retrognathic mandible but with normal positioning of the maxilla in Caucasians11,12 and maxillary protrusion in Chinese.13 However, a population study of Chinese patients demonstrated that only about one-third of the subjects with a Class II dental arch relationship were true skeletal Class II judged from the ANB angle or Wits appraisal, whereas about 1 in 10 subjects with Class I dental arch relationship had a skeletal Class II jaw relationship.14 The lower face height11 can be normal but is often increased (vertical maxillary excess), although it can also be decreased (vertical maxillary deficiency). Clinically, subjects with Class II malocclusion often have a convex profile, whereas others have straight profiles. Lips can be incompetent, especially in subjects with increased lower face height, or “overcompetent” in those with decreased lower face height. The maxillary incisors show at rest in subjects with Class II malocclusion and the smile may vary from excessive (gummy smile) to “not showing at all.”
Dentofacial growth is a very complex process. In the clinical context it is important to realize that the positioning of the mandible depends not only on condylar growth but also on the growth rotation of the mandible,15 which is influenced by the growth direction and rotation of the maxilla and even that of the midface. Consequently the positioning of the mandible over a given amount of time depends on the growth rate and direction of the condyle and, in addition, that of the maxilla and midface. Subjects with vertical growth of the condyle will exhibit an anterior rotation pattern but the existence or lack of incisal contact affects the positioning of the mandible and the size of the lower face height. In subjects with both vertical condylar growth and incisal contacts the rotation center is located at the incisors, whereas in those with no incisal contacts the rotation center will be located more posteriorly (i.e., at the first premolars).15 In the latter group the facial height will be relatively shorter and the chin prominence relatively marked. In subjects with sagittal growth direction of the condyle there will be posterior rotation of the mandible and the rotation center will be located at the molar region; these subjects will have a relatively larger lower anterior face height and the mandible will be positioned relatively less forward. Consequently some subjects with Class II malocclusion have a favorable, unchanged, or worsening sagittal jaw relationship. In orthodontic treatment it is important to use appliances in such a way that the facial esthetics, the positioning of the maxilla and mandible, and the jaw relationship do not deteriorate. Fortunately many Class II subjects have an inherent favorable growth pattern and the prognosis for improvement is good or fair in such cases.3,16 In other subjects the prognosis is poor because of their inherent unfavorable growth pattern. Unfortunately many devices used to treat Class II malocclusion have negative effects on the face; that is, while they improve the occlusal relationship, they might ruin a tentatively favorable growth pattern, seriously worsening the treatment outcome in those with a poor inherent growth pattern. In such cases the growth pattern is often blamed for undesirable treatment outcomes when in fact it is more likely that the orthodontic devices are to blame.
Is it possible that a definite Class II malocclusion improves markedly with growth only? In a longitudinal study of untreated skeletal Class II subjects followed from 12 to 23 years of age, the average change in overjet was a reduction of only 1-mm but the sample comprised subjects with greatly improved occlusion, those in whom there was minimal change, and those who became considerably worse.17 The classical study by Björk and Skieller18 in which 21 untreated subjects were followed during adolescence included subjects with Class II malocclusion. The occlusion was greatly improved and “normalized” in Case 5, whereas it got much worse in Case 12. The records of these two cases18 illustrated how the positioning of the mandible is related to the vertical growth of the maxilla, rather than primarily to the amount of condylar growth. In the subject with worsening Class II malocclusion (Case 12), the condylar growth was almost twice as great as in the Case 5 subject, who showed improved occlusion. However, the Case 5 subject had little vertical facial growth whereas the Case 12 subject had marked vertical growth of the face.
Figures obtained from this sample of 21 untreated subjects demonstrated that conventional cephalometric variables did not express condylar growth well. There was no significant association between the amount of condylar growth and change in mandibular prognathism expressed with the sella-nasion B point (SNB) angle (r = 0.15) and only a moderate association when expressed linearly19 parallel to the upper occlusal plane (r = 0.69). Clinicians still attempt to predict mandibular positioning in patients based on certain features of the dentofacial morphology assessed from lateral head films, despite the fact that Baumrind et al.20 demonstrated almost 30 years ago that such predictions were no better than chance. (For more information, see Hägg and Attström21 and Meikle.22)
The treatment options for Class II malocclusion are growth modification, camouflage treatment, and orthognathic surgery. Growth modification aims to influence the growth of the mandible and maxilla; that is, to reduce the skeletal Class II jaw-base relationship by enhancing mandibular and/or restraining maxillary forward positioning while at the same time controlling the lower face height. The treatment plan must be individualized and the position of the maxillary and mandibular incisors carefully evaluated. In many subjects maxillary incisors might appear protruded when they are in fact in a correct position that should be maintained to allow the lower jaw to come forward sufficiently. If maxillary incisors are to be retroclined, this might prevent forward positioning of the mandible. Changing the position of the incisors could potentially modify and compromise the growth changes.
Orthognathic surgery is a versatile and effective way to treat skeletal Class II malocclusion, with surgery of one or both jaws. Surgery of the maxilla, in one or several pieces with or without extraction of teeth, makes it possible to move the maxilla in all three planes. Any movement of the maxilla in the vertical plane affects the position of the mandible in both the vertical and the sagittal planes. Usually mandibular surgery aims to make the mandible longer and position it forward. Subapical surgery of the anterior mandibular segment allows for decompensation of the inclination of mandibular incisors and correction of the curve of Spee. This surgery in combination with extractions of two premolars provides space to place the alveolar segment with its six anterior teeth posteriorly over the mandibular base. In this way a chin prominence is created, allowing for correction of dentoalveolar compensation and an increase of the overjet, which subsequently allow for more forward positioning of the mandible and increased mandibular prognathism. However, there is the potential for relapse in any orthognathic procedure. The average sagittal relapse rate after bilateral sagittal split osteotomy (BSSO) has been reported to be about one-third, and the larger the movements the greater is the risk for substantial relapse.23 In recent years distraction osteogenesis (DO) has been introduced to increase the length of the mandibular body gradually in an effort to produce more stable results, but the relapse rate associated with this approach appears to be very similar to that of BSSO.24
Limitations of Treatment
Treatment objectives should be realistic and should aim to improve the patient’s appearance rather than achieve “ideal” norms. Even with accurate problem lists, realistic treatment objectives, and skillful treatment, there are definite treatment limitations to both growth modification and orthognathic surgery in subjects with skeletal Class II malocclusion. The role of the individual subject’s soft tissue “envelope” must be considered carefully during planning and treatment. Depending on the choice of orthodontic devices and the way in which they are used, there is a risk that treatment could make the patient’s appearance worse. This is the case when there is a lack of vertical control, especially in the molars. Subsequently, the mandible rotates posteriorly and the lower face height increases, which prevents maximum forward positioning of the mandible.
Recent RCTs on Class II treatment have not demonstrated any positive effect on the mandible following treatment with “growth modification devices.” Tulloch et al.,5 who compared one-phase treatment (i.e., fixed appliance only) and two-phase treatment (i.e., a first phase with bionator or headgear followed by a second phase with fixed appliance), stated that there were “remarkably similar outcomes of treatment with and without early phase 1 treatment.” Later, O’Brien et al.6 concluded that “there are definite disadvantages to the 2-stage approach (Twin-block and fixed appliance) … increased burden, appointments, costs, length of treatment and an inferior final occlusal result.” The American Association of Orthodontists’ Council on Scientific Affairs25 concluded that “functional appliances do not increase horizontal mandibular growth in the long term” and in a recent meta-analysis7 it was stated that “effectiveness of functional appliances on mandibular growth in the short term … provided in early adolescence … [were] probably not very clinically significant.” So it seems that the outcomes of the RCTs have finally answered the question raised by Roux in 1889