Limitations of orthodontic treatment: Class III camouflage

Management of Class III: what are the options?

Essentially, there are two treatment alternatives for Class III malocclusion in the non-growing patient.

Orthodontic camouflage (OC)

This means accepting the underlying skeletal relationship and orthodontically repositioning the dentition to achieve a Class I incisor relationship, hence camouflaging the skeletal discrepancy. The concepts of camouflage treatment were introduced to orthodontics in the 1930s, coinciding with the development of cephalometrics and the belief that facial growth was primarily genetically determined and, therefore, immutable to any orthodontic treatment.

Camouflage treatment can be successful in cases where the skeletal discrepancy is mild to moderate, with good soft tissue aesthetics, no significant asymmetry and an adequate overbite prior to treatment (Table 1). In camouflaging a Class III malocclusion, the effects are dento-alveolar, primarily proclination of the maxillary incisors and retroclination of the mandibular incisors, which results in the lower lip being slightly less protrusive.^{16,17,18,19,20,21,22} In cases that start with a protrusive lower lip, this can be beneficial²³ (Figure 1). Tooth movement to camouflage a severe skeletal discrepancy may be physically impossible,²⁴ or could result in an unacceptable compromise to the soft tissue profile as the over-retraction of lower incisors to create a positive overjet, can result in relative prominence of the chin (Figure 2).

Table 1. Clinical features used to define the limits of orthodontic camouflage (OC) in Class III cases.

Features that suit OC treatment	Features for which OC treatment should be avoided
Skeletal Class I or mild Class III relationship	Retroclined lower incisors
Minimal dento-alveolar compensation (ideally proclined lower incisors, upright/retroclined upper incisors)	Proclined upper incisors
Anterior displacement on closing, with the patient able to achieve edge-to-edge incisor relationship in the retruded contact position (RCP)	Reduced overbite
Average or increased overbite	Increased lower face height
Average or reduced lower face height	Moderate to severe Class III skeletal base relationship
Normal soft tissue features (nose, lips, chin)	No anterior displacement on closing from RCP into ICP
No transverse skeletal problems	Significant Class III molar relationship

Skeletal

The severity of the underlying malocclusion is one of the key factors in whether it is desirable, or indeed possible, to attempt OC in a Class III malocclusion. While this can be assessed and described clinically, research has primarily been based on the use of cephalometrics. Numerous, generally retrospective, studies have tried to define the limitations of orthodontic treatment for Class III malocclusions.^{28,31,32,33,34,35,36,37} These usually involve the assessment of a series of cases to define them as either treatable, with or without recourse to OGN, or cases that had been or could be successfully treated with either modality. Dividing the samples into participants who were or should be ideally treated either with OC or OGN, simple univariate analyses or multivariate analysis, generally in the form of discriminant analysis, a statistical technique for categorizing data into groups, is used to look at the cephalometric dental and skeletal differences between the two groups in hope of either providing a measurement that would provide a ‘threshold’ value or an algorithm created from a number of measures that provides an indicator of whether OC or OGN is the appropriate treatment approach (Table 2)

As Class III is not a single entity and has numerous phenotypes, unsurprisingly these studies have thrown out a variety of parameters that seem to influence treatment decisions. Those most commonly reported, where there was a difference between the OC and OGN groups pre-treatment, were the angulation of the lower incisors to the mandibular plane, ANB, Wits, inter-incisal angle, Holdaway angle, SNB, the maxillary/mandibular unit length ratio (M/M) and the gonial angle. No studies found a pre-treatment difference between the OC and OGN groups in relation to the sagittal position of the maxilla as measured by SNA, and only one found a difference in relation to the angulation of the maxillary incisors, with those in the OC group being more retroclined by 5°.³⁵ This would imply the determining factors seem to be primarily related to the degree of dento-alveolar compensation of lower incisors and the underlying sagittal discrepancy as reflected in the relative degree of mandibular prognathism and the convexity of the profile.

What is also apparent is that the vertical growth pattern is important, with patients exhibiting a hyperdivergent facial form being less amenable to camouflage treatment. This, in part, is accounted for in the Wits analysis, because it uses the functional occlusal plane as its reference line, and this rotates downwards and backwards in cases with an increased maxillary–mandibular planes angle. It is also reflected in the use of the gonial angle in three of the studies as a discriminator between Class III malocclusions that were amenable to OC, and those that would require OGN to treat them. The difficulty of OC in high-angle cases may in part be due to the reduced overbite or anterior open bite that is often found, which any proclination of the upper incisors would worsen. Furthermore, the lower incisors tend to be relatively upright or retroclined, which combined with the narrower symphyseal bone and thinner gingival biotypes often found in such patients, means physically there is less scope for further retroclination and dento-alveolar compensation, because this would result in the loss of labial attachment and predispose to recession (Figure 3).²⁴

As well as the A-P and vertical discrepancies inherent in a Class III malocclusion, the transverse relationship also needs to be considered, especially in relation to asymmetry. Kochel et al presented an updated model to the one originally proposed by Stellzig-Eisenhauer et al that included mandibular deviation.^32,35 This, however, did not increase the accuracy of the prediction of the model.

When the mean measurements reported in these studies are looked at there is a large range, with much crossover between the OC and OGN patient groups and across the studies. It is apparent that there is no single measurement or formulae that can provide the answer (Table 3). One of the inherent problems is that to perform a valid and reliable discriminant analysis, certain assumptions and conditions need to be met, including having a large and representative sample size. The studies listed are all retrospective or cross-sectional and have small sample sizes, which may lead to biased, inaccurate or misleading results. Owing to the selection criteria for inclusion, where there is generally a baseline cut-off to classify a case as Class III, as seen in Table 3, there is a large range in severity. This means that they are not looking primarily at the borderline cases where the treatment planning is difficult, but a wider range of Class III malocclusions, including those on the extremes, where it is easier to make decisions. They also are heterogeneous, using different measurements and samples from different ethnic groups with different cephalometric norms. This makes interpretation difficult, and therefore, the application of the results must be exercised with caution especially when being applied to different ethnic groups.

Soft tissues

In Ackerman and Proffit's classic paper, they defined the treatment limitations in what they described as the soft tissue envelope in which the dentition develops.³⁸ The soft tissue constraints on orthodontic treatment are as follows:

In Class III cases, this envelope is affected by the underlying skeletal pattern, which can result in dento-alveolar compensation, typically retroclination of the lower incisors and proclination of the uppers. The extent of this will, in part, determine what further orthodontic tooth movements are possible. If the lower incisors are already significantly retroclined, further retroclination may not be advisable or even physically possible.²³

Facial aesthetics

Facial aesthetics are important to assess and a big determinant for deciding between OGN and OC treatment. Maxillary hypoplasia is associated with paranasal hollowing, flattening of the malar bases, a reduced nasolabial angle and increased scleral show. Mandibular prognathism can result in excessive prominence of the lower lip and chin. There is also a higher incidence of asymmetry in Class III cases, all of which maybe a concern to the patient.

A maxillary hypoplasia can lead to a lack of incisor show at rest and on smiling and, therefore, poor dental aesthetics. OC is unlikely to improve this and indeed can make it worse if the upper incisors are proclined (Figure 4). In cases of mandibular prognathism, retroclination of the lower incisors will result in lower lip retraction, relatively making the chin look more prominent (see Figure 2).^21,22 This is also affected by the form of chin and symphysis, with high-angle, hyperdivergent patients often having thinner symphyses and less prominent, flatter chins. Aesthetically, the lower lip should be as prominent as the chin so any further retraction can result in poor soft tissue aesthetics.

It is, therefore, important to assess the face both in profile and from the front. If there is a good profile in centric relation, this would be an indicator that the case is amenable to treatment with OC.³⁹ The Holdaway angle can also be used, and this has been found to be an important discriminator between cases that can be treated with OC and those that require OGN. This is the angle formed between the soft tissue plane, soft tissue nasion to soft tissue pogonion, and the H-line, a line drawn from soft-tissue menton tangent to the upper lip.⁴⁰ This has an ideal value of 10° when the facial convexity is normal, lower values being indicative of a skeletal III relationship. Threshold values distinguishing between surgical and non-surgical cases have been reported of 3.5° by Kerr et al, 7.2° by Benyachi et al and 12° by Rabie et al, the latter being above the ideal angle of 10° reported by Holdaway, but representing a Chinese population.^30,32,33 This emphasizes the importance of ethnicity in making these decisions using cephalometric norms determined in European patients.

Dental

OC treatment for Class III invariably involves proclining the upper incisors and/or retroclining the lowers, increasing dento-alveolar compensation. The limits of this depend on many factors, including the vertical growth pattern, the width and quality of the alveolar bone and the gingival biotype. While it is possible to retrocline the lower incisors a significant degree in the attempt to camouflage a Class III malocclusion, there is a hard and soft tissue limit. The lower incisors are susceptible to recession if retroclined, especially in high-angle Class III cases with a narrow symphysis and pre-existing thin biotype.^41,42 While the risk of recession is less when the upper incisors are proclined, excessive proclination increases the risk of non-axial loading, fremitus and mobility (Figure 5).

Attempts have been made to put cephalometric figures on these limits. Steiner produced his cephalometric ‘sticks’ that allowed for the modification of the angulation of the upper and lower incisors based on the ANB angle.⁴³ Tweed based the placement of the lower incisors on the angle between them and the Frankfurt plane, which in turn is influenced by the Frankfurt mandibular planes angle and the vertical growth pattern.⁴⁴ Bennett and McLaughlin developed the soft tissue cephalometric analysis (STCA) based on the work of Arnett and Fastlight.^45,46,47 They stated that the upper incisors could be proclined to 120° to the maxillary plane and the lower retoclined to 80° to the mandibular plane, dependent on the size of the thickness of the symphysis and the amount of bone available.²⁴ This has been supported by a study looking at the limits of incisor movement in Class III OC cases, which found the maxillary incisors being 120° to the sella-nasion line and the mandibular incisors 80° to the mandibular plane.¹⁸ It may be possible to retrocline the lower incisors more than this, but this should be done with caution owing to the risk of loss of attachment and the impact on facial aesthetics (see Figure 3).¹⁸

Occlusal

The presence of an anterior displacement from centric relation to centric occlusion is a favourable sign that OC is possible because it indicates the underlying skeletal relationship is only mildly skeletal III or even skeletal I, often described as a pseudo Class III relationship. As long as there has not been excessive dento-alveolar compensation, cases that present with a significant forward displacement are usually amenable to OC (Figure 6).

The buccal segment also needs to be assessed in relation to the molar and canine relationship. Therefore, one of the further parameters suggested by Lin et al that indicate a case is treatable with OC is a Class I buccal segment relationship in centric occlusion.³⁹ If the molar relationship is not Class I but Class III, it does not mean the case could not be treated with OC, but rather that space will be required in the lower arch for retraction of the canines into Class I to achieve a Class I incisor relationship. This can be created with lower arch extractions. This is usually lower premolars (Figures 7 and 8), but lower first molars can be considered especially if they are restored (Figure 9).^16,48 Alternatively, the buccal segment relationship can be corrected by retraction of the whole lower dentition, which has been made possible by the use of skeletal anchorage.

Patient expectations

While it may be successful in correcting the malocclusion, OC treatment will not change the underlying skeletal relationship or profile significantly. Therefore, it is important to ascertain the patient's concerns because this is crucial to deciding between OC or OGN surgery. If a patient is happy with their facial appearance, OC can be confidently undertaken (Figure 10). However, if the main concern is facial appearance and chin prominence, OGN surgery should be recommended (Figure 11).

OGN surgery for Class III malocclusions in non-growing patients is predictable and stable in the long term, especially in maxillary advancement and bimaxillary surgery.^{49,50,51,52,53} OGN results in improvements in quality of life both physically and psychosocially after surgery, and is associated with high patient satisfaction rates.^49,50,54 Similarly, patients with a Class III malocclusion who receive OC treatment also report high degrees of satisfaction.^17,55 In the small number of dissatisfied patients, this was a result of the residual mandibular prognathism. Therefore, if a presenting patient expresses concern about the relative prominence of their chin, this is an indication that OGN surgery may be the most appropriate treatment option.

Conclusions

The treatment of Class III malocclusions remains a challenge. Numerous studies have attempted to identify dental and skeletal parameters to assist in clinical decisionmaking, the commonest reported being the Wits and Holdaway analyses. However, no simple figure or equation has determined the best treatment in borderline cases. Other factors are equally as important, most notably the patients’ concerns and expectations. Treatment decisions need to factor these in as part of a shared decisionmaking process.