Orthodontic extractions: history and current trends

Edward Angle – In the beginning…

It was Edward Angle, the father of modern orthodontics, in the late 19th century who originally defined a ‘normal occlusion’ and then further classified deviations from the ideal, namely malocclusion, based on the molar relationship.¹⁰ He believed that, provided a Class I molar relationship was present, everyone had the capacity to have all 32 permanent teeth aligned within their jaws, giving them the optimum function and aesthetics.¹¹ The justification for this was based on Wolff's law, namely that bone would form as a result of the forces applied to it when moving the teeth. Furthermore Rousseau, a philosopher of the time who was focused on the ‘perfectibility of man’, suggested the problems of modern man were environmental in origin, and as such orthodontic extractions would prevent the attainment of perfection. There was also support for the aesthetics of this approach, by a friend of Angle, Edmund Wuerpel, an eminent artist of the time. He helped develop ideal aesthetic criteria, suggesting that the best facial and dental aesthetics occurred when all 32 permanent teeth are placed in an ideal occlusion. Angle claimed that his appliances, by moving the teeth into their correct positions, would grow bone and give the optimal aesthetic result. At the same time, the restoration of teeth was becoming ever more a reality, making their extraction for orthodontic purposes less necessary. Orthodontic relapse was also blamed on a failure to achieve an ideal occlusal outcome. These factors ultimately led to most of Angle's cases being treated on a non-extraction basis, with expansion of the arches and incisor proclination providing the necessary space for tooth alignment.

Aesthetics and stability

Calvin Case, a professor based in Michigan USA, opposed the ideas of Angle due to the excessive dental protrusion such treatment created, which he considered unaesthetic.¹² He supported an extraction approach.¹³ Case challenged Angle's treatment philosophy at a meeting of the National Dental Association, which later became labelled the ‘The Extraction Debate of 1911’. However, Case lost the argument resulting in his ideas being largely ignored therefore extractions were rarely prescribed for orthodontic reasons.

It was not until after Angle's death in 1930, that Charles Tweed, originally a student of Angle, became concerned about the amount of relapse in cases assessed 25 years post-retention.¹⁴ As such, he re-treated a few cases with four first premolar extractions and the results, in his opinion, were not only more aesthetic, but more stable.¹⁵ He was also particularly interested in the lower incisor position as a marker of stability.

Modern diet

Raymond Begg, a classmate of Tweed working in Adelaide, Australia, independently noted similar concerns regarding stability and aesthetics and so also adopted an extraction approach. Begg, however, also argued there was insufficient space in the arches for the full permanent dentition in an era of soft modern diets. This idea was based on an examination of Aboriginal skulls, which showed significant dental abrasion and therefore a lower dental-alveolar ratio.¹⁶ In modern humans, the combination of a softer diet and less abrasion, along with a smaller jaw size, means that there is a higher dento-alveolar ratio, resulting in insufficient space for the teeth to be aligned. Begg, therefore, argued that extractions are justified in order to compensate for this lack of non-carious tooth surface loss and the other anthropological changes seen. It was also at this time that Begg was developing his own appliance system, fundamentally based on the principles of extractions as an integral part of the treatment.

The theories of Case, Tweed and Begg slowly gathered pace and combined with ever-increasing evidence and professional experience of the stability and aesthetics of a non-extraction treatment, resulted in a ‘boom’ of orthodontic extractions. By the 1960s and early 1970s, orthodontic extraction rates were as high as 80%.⁵ This was frequently four first premolar extractions in the then held belief that this would ensure stability. As time moved on however, orthodontic extraction rates went into decline (Table 2).

Aesthetics revisited

When extraction rates were at their highest, Richard Riedel, working out of Seattle, Washington, USA, in the 1950s focused once again on dental and facial aesthetics. He noted the ability to significantly alter facial profiles through orthodontic treatment and also reported that there was a public preference for a fuller profile,¹⁷ as facilitated by a non-extraction approach. This preference was noted from as far back as the first sources of aesthetic idealism, from profile drawings of Apollo Belvedere right through the 1950s with analysis of beauty pageant winners.

Returning to relapse

In the 1980s, Richard Little in Seattle assessed 65 cases treated with extractions and edgewise mechanics at least 10 years post-retention, and reported that 70% showed crowding in the incisor region, 20% of which were deemed to require re-treatment.¹⁸ He analysed more closely the arch form changes that had taken place, not only in orthodontic cases, but in normal untreated cases as well. He found that there was a steady decrease in intercanine width and an increase in lower incisor irregularity from the age 13 years onwards.¹⁹ It could therefore be argued that if all cases relapsed, then extractions were of no major benefit. However, Little's work, among other research,^20,21,22 has shown that although relapse does occur in most cases, extractions might reduce the amount of relapse, and aid stability when compared to non-extraction treatment. Although relapse might be reduced, the fact that it will indeed happen in a large proportion of cases has helped shape the current thinking that orthodontic retention is now a life-long commitment, if dental alignment is to be maintained throughout life.

Bonded retainers

It is argued that the development of ‘adhesive dentistry’ has been one of the biggest advancements in the history of dentistry.²³ It began in the 1950s when Buonocore demonstrated the benefits of acid etching and the creation of micro-mechanical retention, such that macro-mechanical retention was no longer an essential requirement.^24,25,26 Since then, bonding technology has evolved through to the current eighth generation of bonding systems.

Direct bonding has revolutionized orthodontics in two ways. First, prior to direct bonding, bands would be placed on each individual tooth in order to generate enough purchase to facilitate the application of orthodontic forces. However, this resulted in the creation of significant spaces between teeth once the bands were removed. Direct bonding allowed brackets to be placed without interfering with the interdental spaces.

Secondly, fixed retainers could be bonded discretely to the lingual surfaces of the incisors and canines. Prior to this, a fixed retainer was only affixed to the canines with a bar passing behind and in contact with the incisor teeth that was not only unaesthetic, but would also not necessarily prevent lower incisor rotational relapse. There was also a high risk of decalcification or decay developing around the bands should microleakage occur. In the 1970s, Knierim was one of the first to report on an ‘invisible lower cuspid to cuspid retainer’ in which round orthodontic wire was held in place using the acid-etch technique in combination with a composite resin.²⁷ Since then there have many developments, with Zachrisson being an advocate of multi-stranded wire²⁸ in the hope that the inherent flexibility would allow some physiological tooth movement and reduce the chance of retainer debond during service. Later developments with composite fibre retainers were also marketed with improved aesthetics. However, these are more rigid and appear to have a higher failure rate.²⁹ Although there is currently limited evidence as to the ‘best’ fixed retainers, they have been shown to be useful additions to an orthodontist's armamentarium for retention. Fixed retainers are also now more popular than ever due to patient factors, such as acceptable aesthetics with ‘invisible’ or minimally invasive wires, as well as removing the onus of compliance that comes with removable retainers (Figure 2). There is some evidence suggesting they maintain alignment as well as, if not better than removable retainers.^30,31 Furthermore, bonding techniques now make it feasible to produce a good long-term result that requires minimal maintenance by patients and clinicians. It also enables unstable tooth movements to be achieved and maintained in the longer term, with the aim of producing better facial or dental aesthetic outcomes.

Interdental enamel reduction

In the 1980s, John Sheridan, an orthodontist from Louisiana, USA, developed Begg's theories of dental attrition further. He argued that, if enamel can be safely removed by nature, then it should be possible to be replicated in the orthodontic office (Figure 3).³² Much of the work surrounding interdental enamel reduction has focused on assessing the stability it may promote, as well as any negative effects on the dentition. To date, it is considered a safe procedure to carry out provided a suitable protocol is followed.³³ As much as 8 mm of space per arch can be gained if all contact points are available.³⁴ There is some evidence to suggest that stability is improved. However, this evidence is weak and is mainly based around lower incisor crowding.^35,36,37

Temporomandibular joint disorder (TMJD)

In 1987, there was a landmark legal orthodontic case in the USA, namely Brimm vs Malloy.³⁸ The prosecution argued that the orthodontic treatment provided to a 16-year-old girl, involving headgear and premolar extractions, had resulted in TMJD. It was argued that the treatment and mechanics employed had over-retracted the incisors, resulting in joint issues. At the time there was little evidence available to argue against this and the orthodontist lost the case at a cost of $1 million. This resulted in a rapid increase in research into orthodontic treatment and TMJD, and the current evidence suggests that orthodontic treatment does not cause TMJD³⁹ and cannot be used to treat it. However, the successful prosecution of an orthodontist is likely to have resulted in more clinicians leaning towards non-extraction treatment, as well as patients demanding a non-extraction approach for fear of developing TMJD.

Self-ligating brackets

Self-ligating bracket systems have been around since the 1930s (Figure 4). However, they gained significant attention when the Damon system was heavily marketed in the 1990s. A number of claims were made for the appliance, including lighter forces, lower friction, shorter treatment times and reducing the need for extractions to below 5%⁴⁰ due to ‘arch-development’. These claims are mostly unfounded,^41,42 but an active marketing campaign, re-branding of arch expansion, is likely to have contributed towards a reduction in extraction treatments despite the inherent instability of arch expansion.

The internet has not only resulted in patients being able to more easily access information about orthodontic treatment themselves, but also in them being targets of direct marketing, which is likely to have also contributed to a reduction in extraction treatments.