Introduction

The delivery of healthcare in the UK has seen considerable change in recent years with the reconfiguration of NHS healthcare commissioners, increasing emphasis on patient-reported outcome measures, and budgetary restrictions. Dentistry has not been immune to these developments with contractual changes particularly noteworthy. Historically, orthodontic treatments were predominantly undertaken by non-specialist general dental practitioner (GDP) providers within the NHS, but this situation gradually changed with the acceptance that fixed appliances in the hands of specialists were capable of superior results.1 In recent years, however, alternatives to conventional courses of fixed appliance orthodontics have emerged. Much of this treatment is offered by GDPs, predominantly in the form of 'accelerated orthodontics' or treatment involving aesthetic removable and fixed appliances2 but this has been accompanied by a significant increase in successful litigation claims.3

Similar patterns of care, with delivery involving both specialists and non-specialists, have been observed in other dental disciplines including paediatric dentistry4 and periodontics,5 and are also established internationally in orthodontics.6 What differentiates this trend within orthodontics from that in other specialties is that a significant proportion of the treatments offered by general practitioners have more limited objectives than conventional specialist-delivered care; some of it is also suggested as an adjunct to produce a more conservative restorative solution than would be possible without recourse to orthodontics. In this paper, nine areas of debate and misunderstanding concerning orthodontic planning and treatment are discussed.

Are molar relationships relevant?

The ideal Class I molar relationship was originally defined by Angle7 and later refined by Andrews.8 Angle's initial belief was that the molars were the cornerstone to the occlusion. While adolescent growth may alter skeletal relationships, typically reducing the convexity of the lower face and improving skeletal II relationships slightly,9 molar relationship is generally considered to be constant once the permanent dentition is established.10 The molar relationship is integral to determining the final incisor relationship. Specifically, with Class I molar relationships and an intact dentition devoid of inter-arch tooth-size discrepancy, non-extraction treatment is likely to translate into a Class I incisor relationship. Moreover, in the presence of moderate to severe crowding, consideration should be given to symmetrical extraction of four premolar units to preserve Class I molar and incisor relationships.

With Class II molar relationships at the outset in an intact dentition, simple alignment is likely to translate into a residual overjet following treatment. Consequently, consideration should be given to correcting the molar relationship to Class I with one of a number of adjuncts including: a functional appliance, fixed Class II corrector, headgear or upper and lower extractions if achievement of Class I incisors is a treatment objective (Fig. 1). Alternatively, in an uncrowded lower arch, consideration could be given to accepting the Class II molar relationships by camouflaging the incisor relationship with the loss of maxillary premolars alone (Fig. 2). The alternative would be to accept a residual overjet following treatment, but this would have implications both for aesthetics and post-treatment stability, likely requiring a commitment to life-long retention.

Figure 1: In a growing patient this Class II molar relationship was corrected to Class I.
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Consequently, incisor and canine relationships were corrected allowing the overjet to be reduced

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Figure 2: Class II division 1 incisor relationship with Class II molar and canine relationships of the left side.
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Non-extraction treatment without active distal molar relationship to Class I would lead to an increased overjet at the end of treatment. Maxillary premolars were therefore removed and anchorage supported with temporary anchorage devices to facilitate overjet reduction and relief of crowding. The Class II molar relationships were preserved but both incisor and canine relationships corrected to Class I

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Is a Class I incisor worth aiming for?

Traditionally, achievement of Class I incisors has been an objective of comprehensive orthodontic treatment. The rationale for this relates to the likelihood of stability and aesthetics associated with this relationship between the upper and lower incisors. Stability stems from the combination of a normal overjet and overbite with the maxillary incisors resting on the tips of the mandibular incisors, which in turn may be stabilised with a fixed lingual retainer.

Retroclined incisors, characteristic of Class II division 2 incisor relationship, in particular are believed to be a by-product of a high resting position of the lower lip.11,12 While alignment of upper incisors in such cases tends to be particularly rapid, acceptance of a residual overjet is often unwise because of a marked tendency for the lip-to-tooth relationship to re-establish itself following treatment.10 It is, therefore, highly likely that the maxillary incisors will retrocline following treatment in the absence of the stabilising effect of the lower incisors.

Occasionally, a decision may be made to accept a residual overjet in the presence of a skeletal II discrepancy not severe enough to warrant orthognathic correction, whereby retraction of the maxillary incisors would compromise the support of the upper lip. In such instances, permanent bonded retention is mandatory and the potential instability of the outcome should be discussed during the informed consent process.13,14

Should non-extraction treatment be undertaken wherever possible?

The reliance on extractions as part of orthodontic treatment has fluctuated over the decades. At the turn of the twentieth century, Edward Angle espoused non-extraction fixed appliance treatment with 'arch development' involving buccal expansion and incisor proclination.15 After initially following this philosophy, Tweed subsequently abandoned such an approach, on the basis that 80% of his recalls had poor facial aesthetics, occlusal instability and irreparable damage of the investing tissues of the teeth in the incisor and premolar regions.16

As a consequence, in the period between the early 1950s to the late 1970s, many orthodontic patients underwent premolar extraction in the expectation of enhanced post-treatment stability. Since then, there has been a widespread desire within the orthodontic community to curb the number of permanent teeth removed for orthodontic reasons; this tenet persists to the present day.

Although there is short-term inconvenience and discomfort associated with dental extractions,17 the severity of associated pain has been shown to be less marked than that arising from the initial engagement of an orthodontic aligning wire.18 In addition, there is no proven risk to either the oral health and function or to the facial aesthetics of an individual who has had dental extractions as part of orthodontic treatment. Moreover, extractions are usually prescribed to relieve crowding in an effort to minimise either transverse or antero-posterior arch length changes during treatment; it would therefore be counterintuitive to expect significant changes in the facial profile to arise with carefully planned treatment. At various times extractions have been implicated in causing (i) temporo-mandibular joint dysfunction (TMJD), purportedly stemming from posterior displacement of the mandible and displacement of the articular disc; (ii) premature ageing, related to the loss of lip support; and (iii) compromised smile aesthetics (Table 1). Careful systematic review of the available evidence has failed to support such views;19 moreover, there is now wide acceptance that extractions have the potential to improve both smile aesthetics and facial aesthetics with careful planning.20,21

Table 1 Adverse effects of orthodontics
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While there is some evidence of enhanced stability with extraction approaches,22 in other research little difference between post-treatment incisor irregularity with extraction or non-extraction treatment has been reported.23,24 Reliable data on the merit of orthodontic extractions cannot be derived from retrospective research due to the inevitable confounding effects of contrasting space conditions, likely to have prompted the extraction decision before treatment. The ideal study to assess this controversial area would be a randomised controlled trial with prolonged follow-up. At present, ethical concerns preclude conducting a trial in this area. However, it is accepted that the decision to extract should be made on an individual basis accounting for space conditions, including crowding, overjet, torque requirements and facial aesthetics. Ideally, such decisions should be supported with formal space analysis.25

Does comprehensive orthodontics take two to three years to complete?

Comprehensive orthodontic treatment encompasses an initial phase of alignment typically in nickel-titanium wires, usually taking in the region of four to six months, followed by vertical, transverse and antero-posterior corrections, space closure and finishing and detailing (Table 2). The duration of orthodontic cases in both adolescence and adulthood is typically in the region of 15 months.26 Treatment involving extractions is usually slightly lengthier than non-extraction treatment.27 Combined orthodontic-surgical care is likely to result in an extension to treatment, although treatment times can be quite variable; similarly, treatment incorporating mechanical eruption of unerupted or ectopic teeth is usually quite prolonged.28,29

Table 2 Rapid tooth movement
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Is treatment faster with modern brackets?

Orthodontic appliances have undergone considerable refinement over the last 30 years. The pre-adjusted edgewise appliance was introduced by Andrews in the 1970s,30 largely based on occlusal cornerstones derived from analysis of untreated ideals.8 Pre-adjusted edgewise brackets were the first to be programmed to impart specific degrees of tip, torque, in-out and rotational control on each tooth thereby reducing the need for wire-bending. The most vaunted and positively marketed development since the introduction of the pre-adjusted edgewise appliance have been self-ligating brackets (Table 3), which incorporate either a slide or clip mechanism to entrap the archwire, removing the need for elastomeric or stainless steel auxiliary ligatures.

Table 3 Be wary of claims regarding novel treatment methods
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However, there is no evidence to suggest reduced treatment times with modern self-ligating bracket systems.31 While these brackets have demonstrated reduced frictional resistance to archwire sliding in laboratory studies, there is now a wealth of prospective clinical evidence indicating that this theoretical advantage does not translate into shorter treatment times. In particular, there have been three randomised trials comparing treatment duration with self-ligation and conventional brackets, none of which has demonstrated a time saving with the newer systems.32,33,34,35

Is torque delivery important?

Torque can be defined as 'rotation without translation' or 'preferential movement of the root with a stationary crown'. Torque is a product of force couples generated between bracket and wire; rectangular stainless steel wires with high elastic modulus and minimal play between wire and bracket slot are necessary for effective torque delivery (Fig. 3). Torque delivery is considered to be an integral part of orthodontic treatment; effective torque delivery is one of six recognised occlusal keys necessary to produce an ideal occlusal result.8 In addition, torque delivery is often important in the buccal segments as alleviation of crowding in round wires results in bucco-lingual inclination changes, which may compromise occlusal interdigitation, overbite and stability. In the anterior regions, appropriate torque contributes to dental aesthetics; the labial face of the maxillary central incisor should lie parallel to the facial vertical for optimal dental aesthetics, with greater requirement for palatal root torque in the presence of increased lower anterior facial height.37 In addition, torque expression is important in producing stable outcomes, particularly where teeth were significantly displaced before treatment (Fig. 4).

Figure 3: Class I malocclusion with severe crowding and palatal displacement of both maxillary lateral incisors (Fig. 3a).
figure 3

Following alignment the lateral incisors have been brought into the correct position; however, there is inadequate labial root torque on the upper left lateral incisor (Figs 3b-c). Thick wires with high elastic modulus are required to address this. Torque delivery can be time consuming but is valuable in terms of prospective stability and dental aesthetics

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Figure 4: This Class I malocclusion with palatally-displaced lateral incisors was treated with fixed appliances (Figs 4a-b).
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Sufficient torque was delivered to the maxillary lateral incisors producing an acceptable aesthetic result following 15 months of treatment (Fig. 4c). Routine follow-up 18 months following removal of the appliances, the result has remained stable despite the lack of bonded retention (Figs 4d-e)

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Are better outcomes achieved with modern brackets?

While novel techniques such as the use of temporary anchorage devices (TADs) have broadened the scope and enhanced the predictability of treatment (Table 4), there is no evidence to suggest that refinement of brackets has been accompanied by better outcomes. Prospective research comparing treatment times with self-ligating brackets have also alluded to comparable levels of occlusal improvement with these systems.32,33,34,35Clearly, the quality of a course of orthodontics is contingent more on the standards and skills of the operator than on the bracket system used. Both labial and lingual customised appliances have been produced, with either brackets, wires or both tailored to the individual patient. Customised lingual appliances have become particularly popular due to the wide variation in the morphology of lingual surfaces, which complicates adaptation of stock brackets to these teeth and has a bearing on torque delivery (Fig. 5).

Table 4 Some newer techniques are well proven and highly effective
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Figure 5: Class I crowded case treated with customised lingual appliances over a seven-month period.
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The lack of uniformity of lingual surfaces mean that stock brackets may have poor adaptation to lingual surfaces making treatment more complex

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Is bonded retention a guarantee of stability?

The increasing emphasis on non-extraction treatment has brought the use of fixed retainers into sharper focus (Table 5). Bonded retention is not without problems: fixed lingual retainers may encourage plaque accumulation with potential periodontal implications.38 Consequently, their use may not be appropriate in the presence of poor oral hygiene. Failure rates with fixed retainers have been shown to be high.39 As such, 'permanent' retention does not remove the requirement that the teeth are placed in positions of soft tissue balance. Additionally, prediction of relapse on an individual basis has proven impossible, invoking the need for a long-term retention strategy for many patients.

Table 5 Fixed retainers will not always hold poorly planned tooth positions
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Furthermore, while bonded retainers may maintain rotational correction of teeth, they may be inadequate to resist soft tissue pressures, for example, those arising following correction of bimaxillary proclination. Consequently, inclination changes and tooth migration may arise despite intact retainers; augmentation of fixed retainers with removable retainers may moderate this tendency. It has also been demonstrated that residual activity in bonded retainers may lead to dramatic inclination changes;40 prolonged supervision of retention is therefore advisable (Fig. 6).

Figure 6: Presentation of an orthodontic case ten years following removal of fixed appliances with rotation and axial inclination changes of terminal teeth on the retainer (22, 43).
figure 6

The changes may stem from residual activity in the bonded retainer wire

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Is inter-proximal reduction safe?

There is long-term evidence indicating the safety of inter-proximal reduction.41 In this research no increased risk of either caries or periodontal problems ten years subsequent to the procedure was demonstrated. All inter-proximal reduction in the study was carried out by an internationally-renowned orthodontist; therefore, while the procedure may well be performed safely, it is important that it is undertaken with care and attention aiming to produce a smooth surface without inter-proximal ledges risking plaque accumulation and associated risk of periodontal compromise, sensitivity and caries progression (Fig. 7).

Figure 7: This patient presented having commenced treatment with a general practitioner with a removable aligner system.
figure 7

The practitioner had undertaken liberal inter-proximal reduction of the lower anteriors to facilitate alignment, introducing unaesthethic morphological changes and ledges inter-proximally. The teeth were subsequently aligned with fixed appliances in less than six months

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Conclusion

Traditional orthodontics involves a complex decision-making process not merely a binary decision of whether one form of treatment is appropriate or otherwise. The treating clinician is charged with choosing between an array of treatment options, appliances and auxiliaries based on a range of considerations including facial aesthetics, dental aesthetics, and intra- and inter-arch relationships. There is a wide diversity of presentations of malocclusion warranting tailored treatment planning and mechanics. Therefore, while short courses of orthodontics performed on a non-extraction basis may improve alignment in the short term, it is important that treatment of this nature is carefully planned, restricted to amenable cases and suitably retained.