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Diagnosis and treatment planning

Nigel Harradine

Chapter

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Introduction The chapter on Occlusal Treatment Goals considers what our occlusal goals should be. This chapter addresses further important questions of diagnosis and treatment planning:

• where would we ideally like to place this occlusion horizontally and vertically within the face? • exactly what aspects of the appearance and function of the teeth and face are a source of

dissatisfaction to the patient? • what are the diagnostic features, which we need to observe to decide how we can find the best

means of satisfying these requirements? • how do extractions affect aesthetics, stability and ease of treatment?

With regard to the first point, the vertical position of the occlusion is also important to remember and we should ensure that our treatment mechanics avoid unwanted extrusion of the molars or incisors. The scope for altering the vertical position of the occlusion orthodontically is covered in other chapters. This chapter will discuss the anteroposterior position of the occlusion and the width of the occlusion. Decisions need to be reached as to what is desirable and what is achievable.

In relation to the second point, a gummy smile is a good example of a dentofacial feature which may or may not bother the patient.

A list of diagnostic features relating to these aspects is clearly required and also decisions about how best to assess them.

The last part of this chapter focuses on extraction decisions, which are such an important part of the planning process.

It is inappropriate in this manual to deal in detail with all the potentially relevant features, such as measuring the overjet or assessing the molar relationship. Nor is a level of detail appropriate for orthognathic cases included here. Rather, this section is a core checklist to avoid important categories of data being neglected and to suggest appropriate measures in some categories.

The occlusion Important aspects of occlusal planning have been covered in the chapter on Occlusal Treatment Goals. However, other factors, notably dental disease or missing or previously extracted teeth will alter the potential choice of occlusal goals.

Features important in diagnosis The facial soft-tissue profile The two most important features are probably the prominence of the lips relative to the nose and chin (assessed via the lower lip to E line distance or using Merrifield’s line) and the nasolabial angle (NLA). These have their limitations but are also quick and easy to apply and therefore stand a good chance of being incorporated in routine orthodontic diagnosis. One of the limitations of the NLA (Figure 3.1) is that it comprises both the angle of the lower surface of the nose and also the inclination of the upper lip and facial aesthetics in profile may be more influenced by the latter. An angle between a tangent to the upper lip and the facial horizontal (Figure 3.2) might be a better measure of the aesthetics of upper lip profile but is not in common use and the NLA with intelligent interpretation may therefore be preferred.

The Holdaway angle is another well-known measure of balance in facial profile. It has been used in the British Orthodontic Society national audit of successively treated orthognathic cases (Johnston et al 2006), and is now officially recommended by the BOS clinical effectiveness committee as one of seven cephalometric measures to

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audit the outcome of orthognathic cases. OPAL, which is produced on behalf of the British Orthodontic Society, was used to measure and extract the data and the Holdaway angle is

now included in the OPAL analysis. This angle is open to a little confusion both from differences in definition and also depending on whether the correction factor for the skeletal convexity is applied. The original papers (Holdaway 1983, Holdaway 1984) are recommended and fully explain his thoughts with plenty of examples. The norm is entirely his opinion. A paper by Basciftci et al (2003) used this angle and is a good example of the angle in action as a measure of balance in facial profile. The angle in its conventional definition is between soft tissue nasion-soft pogonion and soft pogonion-labrale superius. The larger the facial convexity (i.e. the more skeletal class 2), the larger the angle should be, according to Holdaway. Interestingly, both the Turkish dental students in this paper and the Bolton norms have Holdaway angles at the very upper end of ‘normal’ according to Holdaway. OPAL gives both the uncorrected value and the value corrected for convexity according to Holdaway’s formula. An important point about Merrifield’s line and the Holdaway angle are that they do not include nose prominence in the assessment of facial balance whereas the Rickets E line does.

A relatively straightforward and interesting analysis for assessing soft tissue balance has been proposed by Bass (2003). The anteroposterior positions of the lips and chin are assessed in relation to a perpendicular from subnasale. This analysis is linear as is Ricketts E line assessment but like the Holdaway analysis, disregards the nose. An appealing aspect in principle is the use of a natural vertical obtained from posing during a lateral photograph, which is then transferred to the cephalometric x-ray. This uses a simple protractor and the E line as a reference common to photograph and cephalogram. A simple method of recording natural head posture is intuitively a sensible way to view aesthetics of the soft tissues. Some digitising programs such as OPAL, permit the recording of natural vertical and then make antero-posterior measurements - e.g. of the nose and chin - in relation to it. This method may increase the popularity of using a natural head posture.

The lips The vertical resting and smiling (upper lip) lip lines are important in

Figure 3.1: The nasolabial angle (NLA). This is a well -established aesthetic indicator, but may not be the best guide to aesthetics of the upper lip profile

Figure 3.2: A suggested alternative to NLA. The lip inclination

Figure 3.3: The Holdaway angle. A measure of facial balance which excludes the nose

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relation to appearance and in some cases to the stability of overjet reduction. These can be measured in mm relative to the upper incisor tip. If any upper gum is shown during smiling, this may be a cause of concern to the patient and this possibility should be explored. Interestingly, Johnson and Smith (1995) propose, in a study on smile width, that the most important feature of a smile that both affects aesthetics and is also affected by orthodontics, is the amount of maxillary gingivae displayed. Their examples of smiles judged to have a poor appearance by a lay panel seem to support this view.

The A-P and vertical skeletal pattern and the incisor inclinations A well-known variety of cephalometric parameters exist for these assessments.

Temporomandibular joint dysfunction Although clinically significant signs and symptoms seem uncommon and there is good evidence that orthodontic treatment does not cause this potential problem, it is quick and easy to at least be aware of the existence and extent of any signs and symptoms.

• joint noises? • discomfort with jaw movement / muscle tenderness? • amount of opening and lateral excursion in mm. This can be recorded in the notes in simple

diagrammatic form and is a good objective sign of a change in actual joint dysfunction. Opening is usually > 40 mm and lateral excursion > an upper incisor width.

The patient's actual complaints For example: Is the patient bothered by the prominent upper teeth or also by the receding chin? This may profoundly affect the chosen plan in cases of borderline skeletal severity. Is the patient bothered by the appearance or function of an anterior open bite or is it the long face or the gummy smile that are the main concern? This may strongly influence the choice between Young Kim type orthodontic mechanics and a Le Fort osteotomy.

Patient compliance The literature has to date been largely unhelpful in identifying predictors of lack of patient compliance. Mid-treatment indicators such as a failure to attend or to progress in the early stages of treatment are of some help, but we still have almost no scientific ability to pick winners in advance. The study by O’Brien et al (2003) did show that a geographical measure of likely social deprivation (the postcode) did significantly predict levels of compliance with functional appliances. However, it is debatable as to how much we would alter the treatment plan in the light of the patient’s address.

Age and sex Spontaneous space closure has been clearly shown by Stephens and Houston (1985) to be highly related to the rate and amount of remaining growth. Johnston has shown (e.g. Livieratos and Johnston 1995) in studies using his pitchfork analysis (Johnston 1996) that in a growing patient, a significant part of the correction of a class 2 molar relationship in a non-extraction case is, on average, due to temporary inhibition of maxillary growth and continuing mandibular growth. This is clearly a large factor to consider when choosing mechanics in a patient with little or no remaining growth.

The problem list Having gathered all the relevant data, we would strongly advocate the compilation of a problem list before deciding on treatment aims and subsequently, treatment means. The advantages of a problem list can be summarised as follows:

• it turns a mass of data into a short and relevant list • no problems are forgotten – at the treatment planning stage or later

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• it focuses thought on the actual problems • it enables problems to be recorded as fully noted, even if the subsequent list of treatment aims

includes a decision to accept a problem rather than to attempt to resolve it.

These are powerful advantages in making good plans, in keeping track of treatment aims during treatment and in recording the limitations of treatment aims. A list of treatment aims will of necessity address all the problems in the list and will lead to a rational selection of the best means of treatment for that patient

The sequence of forming a plan should therefore be:

• compile a problem list • list the treatment aims • list the treatment means

General and specific treatment aims Any specific list of treatment aims will be compiled against an underlying set of general treatment aims or principles. For example, we need to have answers to all the following questions:

• what final occlusion do I normally aim for? • what general aims do I have about changes in arch width and shape? • what do I believe is desirable/achievable regarding vertical tooth position? • what general aims do I have for antero-posterior lower incisor position? • what are my general views about the effects of extractions and what factors influence my choice of

extractions?

All these questions are addressed in one of the chapters of this manual, with the last two being a particular focus of this chapter. It will not surprise readers to hear that we feel that every orthodontist needs views on these questions that are based on the best available evidence, although it needs to be recognised that the current evidence is far from ideal on many of these points. A paper by Lysle Johnston (1998) is typically iconoclastic on this subject and very well worth a read. It is entitled “The value of information and the cost of uncertainty: who foots the bill?”

Antero-posterior incisor position This is a highly important part of any treatment plan. Given that our occlusal goals usually include a class I incisor relationship, the question becomes one of where to aim to put the lower incisors. This should be considered first in its own right and then in relation to extraction philosophy since this a very important determinant of final lower incisor position. This question is very amenable to cephalometric analysis and many well-known cephalometric goals for lower incisor position have been advocated. Those by Tweed, Steiner, Merrifield, (1996) Ricketts, Downs, Mills (1966) and Holdaway are representative (see the book by Athanasiou 1995). The questions that should be asked about any goal for incisor position are:

• does it produce results that are more stable? • are the results more aesthetic? • does it facilitate a good occlusion? • can the planned position be more easily achieved than others? • is the planned incisor position conducive to long-term dental health?

Stability and lower incisor position The most crucial questions are the first three. Regarding stability, few people now dispute that no treatment goal is likely to produce more stable results than those obtained when following Mills’ goal (1968) of aiming to leave

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the average incisor labiolingual position unchanged during treatment. The question is whether other guides to end-of-treatment incisor position will produce results that are equally stable anteroposteriorly. In the past, many have claimed or implied - contrary to Mills’ findings - that their analysis or goal will consistently produce substantial and stable labiolingual change in lower incisor position. The evidence to support this is very slim although individual cases of such a stable change undoubtedly occur. Mills (1966) found that lower incisors which were proclined or retroclined by a minimum of 7 degrees during treatment relapsed by an average of 50% post-treatment. The extent of these post-treatment changes correlated significantly with the amount of labiolingual movement, although there were unpredictable individual exceptions. A study by Houston and Edler (1990) provided strong evidence that the APo line is not a position of lower incisor stability. They also found that in 62% of cases the incisors tended to return towards their starting A-P position. In the remaining cases, the post-treatment A-P changes were haphazard. More recent studies have produced similar findings. Hansen, Koutsonas and Pancherz (1997) found that incisors proclined an average of 11 degrees or 3.2 mm retroclined an average of 8 degrees or 2.5 mm in the following six months when no appliances were in place. Stucki and Ingervall (1998) found that on average 70% of the proclination produced by Jasper Jumpers subsequently relapsed.

Sims and Springate (1995) investigated more modest A-P alterations in lower incisor position and found a similar tendency for incisors moved labially during treatment to return towards their starting position, but found that modest retroclination of incisors was stable or even increased post-retention. This is one of several hints in the literature that invasion of the space previously occupied by the tongue is more stable than invasion of lip or cheek space. These authors also commented on the wide standard deviation of post-treatment change around the average changes.

A study by Williams and Andersen (1995) investigated the very interesting idea that lower incisor proclination might prove to be stable in those patients in whom the mandible is expected to develop in an anterior rotational pattern according to the morphological features described by Bjork. The treatment would in effect be taking advantage of the natural tendency for lower incisors to compensate by proclining as the mandible rotates anteriorly. The authors found an average proclination during treatment of 9 degrees with an average relapse of 3.4 degrees and an average treatment change relative to APo of 2.7 mm with an average relapse of 1.2 mm. The degree of relapse was very significantly related to the amount of labial movement or proclination although some cases were a marked exception to the general rule. Disappointingly, anterior rotators are no more likely to permit stable lower incisor proclination than other groups.

This paper therefore supports the previous studies, but can similarly be interpreted in two ways:

• proclination tends to be unstable

or alternatively,

• approximately 60% of the proclination remains

Both these statements are true, but many clinicians seem to recall only one of them. Several details of the study by Anderson and Williams are worth noting. Firstly, all cases were retained until skeletal maturity (hand-wrist radiographs) - an average of 3.3 years. Secondly, the post-retention Little’s index was much better than most of those reported by Little (1990) (2.8 mm vs. 4.7 mm). Was this due to the long retention until cessation of growth or is it related to the anterior growth rotation? Thirdly, the relapse in lower incisor labial movement was not related to the relapse in Little’s index, which again proved hard to statistically attribute to any parameter other than expansion during treatment of the intercanine width. Finally we should note that not all of those predicted to rotate anteriorly, actually did. Also, marked pogonial growth made some cases appear to have no linear movement of the lower incisors in spite of definite proclination relative to the mandibular plane. An interesting paper!

Key point: Stability of A-P incisor change is not statistically related to stability of irregularity. “Stability” can mean different things.

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Paquette et al (1992) also found that cases which had been treated with an average of 2.8 mm. more lower incisor proclination than another matched group of cases, finished with slightly greater irregularity (Little’s index) out of retention. The difference in post-treatment relapse of irregularity between the two groups was very small (0.6 mm), but the findings did suggest that labial movement of lower incisors during treatment does, on average, increase the chance of subsequent relapse.

No study has demonstrated consistent anteroposterior stability in a group of orthodontic cases in which the lower incisors have been significantly changed in their A-P position during treatment. Reviewing current knowledge on the ability of the soft tissues to adapt to lower arch expansion, Ackerman and Proffit (1997) propose an approximate limit of 2 mm for labial movement of the lower incisors if anteroposterior stability is the main factor influencing our decision.

It is of interest to detour for a moment and note that Artun et al (1990) found that substantial (>10 degrees) proclination of lower incisors was not associated with greater subsequent relapse than a group treated without proclination. However, these were severe Class 3 patients who, subsequent to lower incisor proclination, had a backward mandibular sagittal split osteotomy; i.e. if the soft tissue environment is radically changed by surgical repositioning of the jaw, the usual soft tissue effects do not seem to apply.

An interesting suggestion is the one formally advocated by Selwyn-Barnett (1996) who points out that in effect the lips cannot ‘know’ which incisor is touching them and that we can therefore procline the lower incisor in class 2 division ii cases to touch the lower lip at the same A-P position as was occupied before treatment by the extruded upper incisor. The stability of the results of such a philosophy has not been well tested, but the resulting plan is often required in any case to achieve occlusal goals (Andrews’ keys 3 and 6) and is a useful way of structuring a plan to procline the lower incisors in such cases, as well as a sensible hypothesis about stability. However, Canut and Arias (1999) found that proclining lower incisors in class 2 division ii cases leads to much more relapse of arch irregularity than when the arch length was not increased. This is salutary evidence that a plausible hypothesis may be incorrect. We aim to retain with particular care Class 2 division 2 cases in which we have substantially proclined the lower incisors and with increasing emphasis on informed consent, prior information about the need for and importance of retention is especially relevant in these cases.

An impressive long-term study by Jonsson and Magnusson (2010) over 25 years found that treatments involving extractions produced much less relapse of crowding in both arches when compared with non-extraction cases, particularly in the lower arch. Cephalometrics was not included in this study but it is probable that non-extraction cases involved labial movement of the incisors.

Aesthetics and incisor position Most proponents of a particular anteroposterior goal for the dentition have based their advocacy primarily on the aesthetic advantages. There is, however, very little direct evidence concerning this question. An opinion may be formed based on the fact that the Tweed analysis frequently retroclines lower incisors and the Ricketts analysis frequently plans for labial movement of lower incisors, but what also matters aesthetically in this respect is the anteroposterior position of the overlying lips and this is extremely variable. Park and Burstone (1986) have shown in a very elegantly conceived study that the soft tissue appearance of the lips in relation to a soft - tissue APo line varies enormously even when the Ricketts hard tissue APo line goal is exactly achieved. Achievement of a particular lower incisor position will therefore produce an enormous variety of profiles, although it is still probably true that for any given patient, some lower incisor positions will produce a more aesthetic lip position than others. Even here, opinions vary as to what is an aesthetically desirable goal, treatment to Merrifield’s profile line tending to produce less prominent lips than treatment to Ricketts’ E line for example.

Variability of soft tissue response Quite separate from this question of variability in soft tissues for a given hard tissue position is the fact of the variability of soft tissue response to tooth movement. This is also well documented. Staggers (1990), for example, comparing premolar and second molar extractions, found definite differences in the A-P changes in incisor position between the two groups, but no differences in the changes in soft-tissue facial convexity or of the upper lip relationship to a soft-tissue APo line. Almost all studies show that the soft tissues move much less than the

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underlying teeth. For example, Paquette, Beattie and Johnston (1992) found an average 1.4 mm posterior movement of the upper lip when the upper incisors were retracted by an average of 5.0 mm – an average ratio of 28%. Large tooth movements are therefore required on average to produce clinically substantial soft tissue change, but the variability is huge. In this paper, the range of upper lip anteroposterior change associated with upper incisor retraction was 10.0 mm! Pancherz and Anehus-Pancherz (1993) reported that there was no correlation (r=0.02) between the hard and the soft tissue changes brought about by treatment with the Herbst appliance. More recent papers have continued to find poor correlation between incisor movement and change in the overlying lips. Kusnoto and Kusnoto (2001) found a correlation coefficient of r=0.39 for the upper lip. In other words, the change in incisor position accounted for r2 = 16% of the variation in lip change. The average ratio of movement was 1:4 for lip: incisor change. A paper by Lai et al (2000) suffers from choices in cephalometric values, which greatly lessen the potential usefulness of the results, but still reveals “a large variation in the soft tissue response to dental movements”. The paper includes the result that two groups which differed in their change in upper incisor inclination during treatment by an average of 20 degrees, differed in their change in upper lip to E line distance by an average of only 0.5 mm. This large variation in soft tissue response was emphasised again in a more recent study by Tadic et al (2007) which focused on predictors of change in lip shape and NLA with upper incisor correction in class II cases. They found a large range of change in NLA (40 degrees) and no correlation with incisor A-P change.

Key Point: Changes in anteroposterior incisor position clearly result in much smaller and highly variable changes in the prominence and shape of the overlying lips. Prediction of changes in lip profile is prone to substantial error.

What degree of lip prominence is considered attractive? A final factor when weighing the aesthetic consequences of incisor prominence is the variety of opinion as to what is an attractive degree of lip prominence. This has been investigated in several studies and a good paper which includes a good summary of the literature is the one by Nomura et al (2009). Lay judges from different racial groups were asked to rate lips of varying prominence in silhouette profiles of disclosed racial groups. Several useful findings emerged. For example all judges of all racial groups prefer the lips to be behind Ricketts E line in all racial groups. Hispanic and Japanese judges prefer more retruded lips and white and Kenyan judges have very similar views on lip prominence. This paper repays a read and may help set a target for lip prominence which is more likely to be appropriate for a given patient.

A suggested lower incisor target position All orthodontists need to look at the available evidence and decide their general aims in relation to this important target. As a starting point, the evidence relating to stability indicates that we should aim not to change the antero-posterior position significantly during treatment unless there is a good reason. Most orthodontic cases (as opposed to orthognathic surgical cases) can be treated without significantly altering the labiolingual position of the lower incisors. Also, the aesthetic consequences of changing their position are unpredictable and usually small. However, if this goal of aiming for little change in the initial antero-posterior position is unwaveringly followed, there are several categories of patient where this would have substantial disadvantages.

• in some cases, the aesthetic concerns of lip prominence or inclination are sufficiently marked that they outweigh considerations of stability. For example, in a well-aligned class 1 bimaxillary proclination case, excessive lip and tooth prominence is probably the only potential indication for treatment. Equally, some class 2 cases have a very obtuse nasolabial angle. This can be a strong factor to tip the treatment plan towards surgery. Where surgery is not an option, this factor may sometimes lead to a decision to plan for significant lower incisor proclination to maintain upper lip support whilst reducing the overjet.

• some cases (e.g. some class 2 division ii patients) are impossible to treat to our chosen occlusal goals without substantial lower incisor proclination.

• some cases with reduced or negative overbite require extractions to retrocline the incisors and achieve an overbite

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• correction of class 3 cases without orthognathic surgery frequently requires significant lower incisor retroclination.

• many cases with mild lower arch crowding are very demanding on the wear of class 2 traction if lower arch extractions are prescribed and unwanted incisor retroclination is to be avoided. It is better to move the lower incisors labially to the modest extent required.

• from a purely pragmatic viewpoint, some cases become extremely anchorage demanding if the lower incisors are not moved labially. This point is less frequently mentioned than others such as considerations of profile, but can undoubtedly be a powerful if unstated motive.

Aesthetics versus stability? Small anteroposterior changes in lower incisor position are of little consequence for either appearance or stability. The evidence is that the larger the change, the more these two factors will - on average - conflict. Choosing a position that is less likely to be stable means more emphasis on ‘permanent’ retention and this is the source of a philosophical dilemma. The work of Little and others quoted above has shown that although larger lower incisor changes in position are less stable, lower incisor alignment tends to deteriorate after retention whether or not the anteroposterior lower incisor position has been maintained. Little personally advocates fixed indefinite retention for lower incisors after all orthodontic treatment. In the light of this, two tenable viewpoints have emerged.

Since tooth alignment tends to deteriorate even if we put the teeth where stability is most probable:

• all cases should have indefinite retention and if this is the case, then why should the orthodontist be concerned with minimising spontaneous relapse when all case are to be retained forever anyway?

Or alternatively

• for one reason or another few young patients wear retainers for the rest of their life and it is therefore best practice to try to leave the lower incisors in a position that minimises the probability of relapse when retention is discontinued.

These two approaches are both entirely tenable. At present we favour the second viewpoint as a starting point, but with some definite exceptions for the aesthetic, occlusal and anchorage reasons listed above. A complicating factor for those looking for certainties in life is that all these exceptions are relative and thus open to weighting which varies even between clinicians who would subscribe to the same choice between the two opposing viewpoints. The chapter on Stability and Retention discusses further the evidence about stability in general and the best practical approach to retention in the light of this evidence.

The question of a suitable goal for lower incisor position is inextricably entwined with extraction philosophy and the merits and disadvantages of extractions per se should now be examined - a subject of recently revived controversy.

Extractions versus non - extraction treatment This ancient debate about the possible benefits and disadvantages of extractions is almost as old as orthodontics itself, but has resurfaced more recently with all the heat and fury that apparently occurred at the time of Angle vs. Case (see the articles by Bernstein 1992). In the USA, the debate has on occasion become markedly acrimonious. It is clearly important to look as objectively as possible at the evidence concerning the issues relating to extractions.

Reasons for elective extractions in orthodontics Before examining possible disadvantages of extractions, it is worth reminding ourselves of the reasons for wanting to remove teeth electively.

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• relief of crowding space is provided for crowded teeth without expanding the arches laterally or anteriorly (or in the upper arch, without transferring the crowding to a more distal part of the arch).

• correction of incisor relationship o overjet reduction o lower incisor retroclination to correct a class 3 relationship o providing the space required to move upper labial segment contact points distally as

retroclined upper teeth are torqued to a correct inclination in the correction of a class 2 division ii relationship

o correction of bimaxillary proclination o increase in overbite if the incisors are proclined and the overbite reduced

• provision of anchorage in addition to providing the space for tooth movement, extractions frequently provide additional space which is harnessed to provide intraoral anchorage. Mesial movement of anchor teeth in response to reciprocal forces is therefore possible without the arch having to be expanded anteriorly to accomplish the desired occlusion. Without extractions, no intraoral anchorage is available for distal movement of teeth (except in naturally spaced dentitions or with Temporary Anchorage Devices - TADs) unless incisors are moved labially in one arch or the other. In non-extraction treatment (discounting unpredictable favourable growth), anchorage must be gained extra-orally or from TADs or alternatively, incisors must move labially or buccal teeth must expand. These increases in arch circumference are not always desirable.

Proposed disadvantages of extractions Several potential disadvantages have been proposed:

• mandibular dysfunction • a less attractive dental and facial appearance • longer, more difficult treatment (in some cases) • pain, anxiety and other possible adverse effects of the actual extraction procedure

Key thought: The last three considerations on this list have all contributed to a general downward trend in the rate of elective extractions in orthodontics

Extractions and mandibular dysfunction It has been suggested that extractions may cause mandibular dysfunction by two mechanisms.

• the effect on condylar position within the fossa • loss of vertical face height.

Regarding condylar position, such authors as Witzig and Spahl (1987) and Bowbeer (1987) have proposed that extractions cause “over-retraction” of the upper incisors and that this leads to the condyles being forced posteriorly and hence the articular disc becomes anteriorly placed and hence mandibular dysfunction. The work previously quoted in the chapter Occlusal Treatment Goals demonstrates the paucity of evidence of an association between condylar position and mandibular dysfunction and indeed the inability of orthodontics or restorative dentistry to alter it permanently. With specific reference to extractions, Gianelly (1991a and 1991b) has found no difference in condylar position between those treated with the extraction of four premolars and those receiving no orthodontic treatment. This has been supported by work by Kundinger et al (1991). Luecke and Johnston (1992) found that the temporary effect of orthodontic treatment on condylar position was highly correlated with the mesial movement of buccal segments but not at all with the retraction of incisors. Major et al (1997) used tomography to show that condylar position was unchanged by treatment in both non-extraction and extraction groups. With regard to the view held, for example, by Bowbeer (1987) that extraction of premolars causes a loss of

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vertical dimension and that this causes mandibular dysfunction, Staggers (1990) was unable to find any such effect in a study of premolar and second molar extractions. Kocadereli (1999) also found no difference in change in vertical facial dimensions between 40 cases treated non-extraction and 40 cases treated with first premolar extractions.

It remains possible that extractions predispose to mandibular dysfunction by some other unknown mechanism. However, studies by such workers as Kremenak et al (1992) have found no differences between groups treated with loss of upper premolars, four premolars and non-extraction. Beattie et al (1994) also found no difference in the CMI values for non-extraction cases and extraction cases. In this clever study, the principle of equipoise was used to get two groups matched for all the variables which discriminant analysis had shown to be able to account for the decision to extract or not. In other words, a rare and necessary feat was achieved - to compare the results of extraction versus non-extraction in groups of comparable cases.

Key Point: There appears to be very little evidence to support either of the proposed mechanisms for causation of mandibular dysfunction by extractions or indeed to support any other unknown mechanism. There is therefore no reason to avoid extractions because of concerns about mandibular dysfunction.

Extractions and facial aesthetics Orthodontic treatment involving extraction has also been accused of producing unpleasantly retrusive lips relative to the nose and chin. Studies have certainly shown that it is possible to achieve a degree of long term retroclination of the lower incisors and that this will be associated with the lips being more posterior than would have been the case if the incisors were more procumbent. The variability of soft tissue (lip) position for a given underlying incisor position and the variability of soft tissue response to anteroposterior movement have already been discussed, but it remains true that for a given individual, more posterior incisors means more posterior lips to an unpredictable extent. However, studies comparing the soft tissue changes in patients with differing extraction patterns inevitably encounter the fact that the groups are very unlikely to be balanced in terms of requirements for space and anchorage. For example, Staggers (1990), comparing first premolar and second molar extractions, found that the anteroposterior changes in lower incisor position were only minutely different and the soft tissue changes were very variable, but on average, identical. This would not be at all surprising if the second molar extraction group had much less initial crowding. This study at least shows that it is nonsensical to generalise about the effects of extractions on lower incisor position regardless of other features of the malocclusion and treatment.

Similarly, the studies by Luppanapornlap et al (1993) and by James (1998), both demonstrated that patients treated with extractions had on average slightly more prominent lips at the end of treatment than those treated on a non-extraction basis. This reflected the fact that initial lip prominence was a significant factor in the extraction/non-extraction decision of the orthodontists planning that group of patients. A recent study by Zierhut et al (2000) again showed the small extra lip retraction with extractions (1.7 mm for the lower lip and 1.0 mm for the upper lip) when compared with non-extraction cases, but since extractions had been chosen in cases with slightly more prominent lips, the final average soft tissue profile was identical in both groups. Finally, the study by Shearn and Woods (2000) was notable for showing the wide variety of anteroposterior changes in lower incisor position, which result for all combinations of premolar extractions. This is simply a reflection of all the other variables in the treatment - notably the amount of crowding, of class 2 elastics, of headgear and of differential growth. An opinion that extractions or non-extraction are “good” or “bad” for the profile is clearly simplistic and uninformed.

Key point: All the published data strongly supports the view that orthodontic treatment involving good planning and execution produces very similar profiles in extraction and non-extraction cases.

Lay opinion A good study by Bishara and Jakobsen (1997) involved assessment by lay people of profile changes in class 2 division i malocclusions treated with and without extractions. Lay judges:

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• preferred the profile of normals to the pre-treatment profile of Class 2 division i patients • immediately after treatment, preferred the changes in profile in the extraction group to the

changes in the non-extraction group • two years after treatment, showed no preference for the profiles of either treatment group or for

the untreated normal group • considered the changes with treatment to be very favourable in both treatment groups.

Key point: All the published data strongly supports the view that orthodontic treatment with good planning and execution produces changes in profile which are viewed favourably by the lay public whether or not extractions are involved.

Differences in soft tissue appearance if the same case is treated extraction or non-extraction Of course, the answers to these questions will also be different for different types of malocclusion. Not much evidence, as opposed to opinion, exists on any of the questions, but the study by Paquette et al (1992) referred to above, gave some extremely useful information for one type of malocclusion. The equivalent groups of cases assembled by the equipoise analysis as being equally susceptible to extraction or non-extraction, were unsurprisingly, mild to moderate class 2 division i malocclusions with mild lower arch crowding. The cases averaged 14.5 years post-retention and were recalled and compared aesthetically, for mandibular dysfunction and for stability. Cephalometric analysis of the long term results revealed that the extraction group had lower incisors averaging 2 mm more posterior than the non-extraction group and the lower lip was 1.2 mm further behind E line in the extraction group. However, these measurable and statistically significant differences produced no detectable aesthetic or stability effects. Regarding aesthetics, various assessments of the patients' opinion of the aesthetic changes in their silhouettes and facial photographs both before and after treatment revealed no difference between the groups. Regarding stability, the Little index in the lower labial segment at recall was 2.9 mm in the extraction group and 3.4 mm in the non-extraction group. This difference was again not significant, although the overall reduction in lower labial irregularity was slightly greater in the extraction group (by 1.9 mm.), which happened to be slightly more crowded initially and relapsed fractionally less.

It would seem that in such mildly crowded cases, if they are treated using non-extraction mechanics which only produce mild labial movement of the lower incisors, (average 0.4 mm in this group), it does not matter significantly whether the cases are treated with or without extractions from the viewpoint of aesthetics or stability. Twenty years later a very similar study has been reported by Konstantonis (Angle on line early for 2012). The same equipoise discriminant analysis was used to compare extraction and non-extraction, this time in a sample of class 1 cases. Analysis showed that the extraction decision was based on initial crowding, facial convexity and lower incisor protrusion. This confirms that clinicians were basing their extraction decision on actors relating respectively to stability, facial aesthetics and occlusal fit. Interestingly, the extraction rate in the parent sample was 30% which compared to 55% for the sample treated in the 1970s from which Paquette derived his borderline group In the derived borderline sample, extraction lead to an average of 2 mm greater retraction of the lower lip relative to E line and an increase of 5 degrees in the NLA compared to no change for this angle in the non-extraction group. The superimposed average profiles in that paper show that these differences have a small effect on the facial profile.

These two studies of borderline cases firmly indicate that if it is felt that treatment will be quicker, easier or more pleasant if carried out on a non-extraction basis, then this would be the sensible approach in this type of case. The studies did not investigate these latter aspects, but it seems reasonable to assume for now that if all things are genuinely equal for a given type of case, we should not extract.

An interesting prospective study by Heiser et al (2004), compared two groups with equivalent starting irregularity index (averaging 5.1 and 5.8) treated with and without premolar extractions. It is very probable that the non-extraction group had some labial movement of the lower incisors relative to the extraction group. They measured areas bounded by different parts of the dental arch. The increase in the area bounded by the lower labial segment relapsed more in the non-extraction group, but interestingly, the relapse in Irregularity index was the same in both groups. The connection between change in lower incisor proclination and irregularity index is clearly not a close

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one. For relatively mild crowding, treated in the permanent dentition, extractions possibly confer no significant additional stability of alignment.

However, the impressive long-term study by Jonsson and Magnusson (2010) of cases reviewed more than 25 years after treatment, found that treatments involving extractions produced much less relapse of crowding of greater than 2mm when compared with non-extraction cases, in both arches but particularly in the lower arch. Such a long-term study is rare and for understandable reasons. The authors understandably conclude that non-extraction

cases should receive proportionately more rigorous long-term retention.

In his long-term studies of dental irregularity, Little (1990) identified “lower arch development in the mixed dentition” (i.e. expansion and proclination of the labial segment) as the only treatment regimen to show significantly worse results than others in this respect. Little (2002), again referred to this work in his paper contributing to the section on early treatment which followed the American Association meeting on that subject. The core of his conclusions was that whilst you can hold and use the Leeway space without any detriment to stability, lateral and anterior expansion of the arches at an early age caused a degree of relapse which was “significant and alarming” and this was for cases which only had to have mild proclination to be included in the “expansion” group. Conversely, a paper by Ferris, Alexander, Boley and Buschang (2005), showed that patients with mild crowding but significant irregularity, when treated in the late mixed dentition with RME, arch expansion, interdental stripping and without extractions, had very acceptable stability more than 4 years out of retention. There was no availability of cephalometric data on incisor labiolingual movement, but the arch width measurements showed that a substantial percentage of premolar expansion was stable in this age group. The effect of extraction choices on lateral stability and smile aesthetics is considered below and in the following chapter on Facial Appearance, the Smile and Tooth Aesthetics. It is worth recalling that Little advocates indefinite fixed retention after all treatments whatever the final tooth positions.

Extractions and smile width So far, this section has dealt chiefly with the antero-posterior effects of extractions. Interestingly, the clever study by Spyropoulos et al.(2001) that used computerised modification of photographs, concluded that factors other than profile outline may be more important in facial aesthetics for lay people and it is orthodontists who pay particular attention to the profile. Orthodontic treatment involving extractions has been accused in recent years of causing larger dark intraoral spaces lateral to the buccal segments - a “dark buccal corridor”. However, the study by Johnson and Smith (1995) found no evidence of this and also no evidence that extractions produced less attractive smiles in the opinions of lay judges.

Two more recent studies by Gianelly have looked at the relationship between extractions and width of dentition. In the first, (Gianelly 2003a), he compared a non-extraction group with an extraction of four first premolars group. The principal finding was that post-treatment, canine, premolar and widest molar widths were essentially the same in the two groups. The second similar study (Gianelly 2003b) is more interesting. The first point of note is that he added a measurement at constant arch depth from the upper central incisors and this depth corresponded to the average depth of the molar-premolar contact in a group of non-extraction patients. This is a sound idea, since measurement at a constant arch depth overcomes the problem that non-extraction may well involve distal movement and therefore molar expansion whilst conversely there is frequently molar constriction in extraction case just because the molars move mesially into a narrower part of the arch. The results for this measurement at constant arch depth showed that the extraction group was slightly wider after treatment than were the non-extraction group. This is a good measurement for future studies. The second part of the study was similar to that by Johnson and Smith. Fifty lay judges were asked to rate close up photos of 12 extraction and 12 non-extraction smiles. There were no differences in the aesthetic scores between the groups. Interestingly, the lay judges again seemed unaware of ‘dark buccal corridors’ as an aesthetic factor in smiles, since only one of them

% of cases with > 2mm crowding

Treatment Pre - treatment 25 yrs+

post-treatment

Maxilla

Extraction 16% 0%

Non-extraction 8% 15%

No treatment 4% 6%

Mandible

Extraction 16% 11%

Non-extraction 3% 28%

No treatment 9% 16%

Table 3.1: Jonsson and Magnusson (2010) long term changes in crowding. Percentages of cases with > 2mm crowding

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mentioned it at all. Also there was no difference in the number of teeth displayed in the two groups whilst smiling.

Key Point: When comparing extraction and non-extraction cases, measurement of arch width at a constant arch depth is more informative than measurement of changes in width of a specific tooth

These two studies are similar in many respects to many studies comparing profiles in extraction and non-extraction groups. They are useful in that they look at (and indeed refute) the idea that extraction results in a narrow arch at the dental smile width, but this leaves unanswered what would result if the same cases were treated with the two regimens – especially if the space requirements were substantial. The Gianelly studies naturally involved cases where clinicians had picked horses for courses when choosing to treat extraction or non-extraction. The cases were not matched. One of the conclusions in a thoughtful systematic review by Janson et al (2011) discussed below is that the studies by Gianelly are good research which does indeed support the view that premolar extractions per se do not have a detrimental effect on smile aesthetics.

Studies of buccal corridor spaces Studies using digitally-altered buccal corridor spaces (BCS) are well worth a look, but the results are not yet strongly convincing. A paper by Moore et al (2005), supported the view that the appearance of small buccal corridors is preferred by lay judges, whilst the similar study by Roden-Johnson et al (2005), showed no such effect. Details of study design, such as the extent of the digital alteration or the definition of buccal corridor, are probably important in these investigations. We feel that the measurement and design used by Moore is the more sound. A recent study by Yang et al (2008) is also to be recommended for its innovative but very accessible method of measuring the BCS and found no effect of extractions on BCS. Importantly and understandably, the cases were not randomised for extraction or matched in any way. The following chapter on Facial Appearance, the Smile and Tooth Aesthetics gives a thorough overview of smile aesthetics, but it is helpful here to note the study by McNamara et al (2008), which found no relationship between BCS or upper incisor exposure and smile aesthetics as rated by both lay persons and orthodontists. Here again, we have to be cautious about that finding because BCS was measured using the Smilemesh software program which defines BCS as the distance between the canines and the outer commissure. We would generally prefer to define BCS as the distance from the widest tooth to the inner commissure. Finally, it is worth looking at the illustrations in the paper by Ioi et al (2009) which also used digital alteration of BCS. They found that lay judges preferred smaller BCS. However, in our opinion, their digital manipulation produced a highly unrealistic imitation of a naturally occurring narrow arch, which gave an appearance of extraction of all buccal teeth. A further point in this paper is that the judges were all orthodontists and dental students. Genuinely lay judges are much more appropriate in such a study. These were used in a study by McLeod et al (2011) and interestingly, lay opinion was more fussy in Canada than in the USA about acceptable limits for BCS and for gum exposure on smiling. The illustrations in that paper clearly show the ideal and acceptable ranges for these and other smile features. The authors point out that the narrow focus on the smile area and the specific use of a ‘slider’ to mark the chosen illustrations may well have made the lay judges give a ore stringent view of acceptability that in real life. This question of realistic portrayal of variations in BCS concerned Janson et al (2011) in their thoughtful systematic review of factors influencing smile aesthetics. They concluded that based on studies of actual subjects, BCS on its own has not yet been shown to be a factor in smile attractiveness.

Key Point: Interpretation of research requires scrutiny of the actual dimension which was measured and the specific experimental setup.

Extractions and aesthetics - the study that is needed There are several good studies discussed above that have compared both profile and smile aesthetics in patients who have been treated with or without extractions. In all of these studies, the extraction pattern has – very understandably – not been randomly assigned. Whilst these have been extremely informative, they leave unanswered the question: “How do the smile and profile aesthetics compare if very crowded cases are treated with or without extractions?” This question has recently become much more relevant because some clinicians

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treat virtually everything non-extraction. This change in their practice has in some instances been facilitated by the apparent ease with which crowded teeth can be accommodated using self-ligating brackets. For this study, matched cases are required with large space requirements which are treated with or without extractions. Using the discriminant analysis methods so pertinently applied by Lysle Johnson, such a study must be possible with the cooperation of clinicians of differing philosophies. The results would still leave the question of the stability of expansion as a factor in treatment planning, but would more thoroughly examine the aesthetics of arch expansion.

Planning extractions In the light of the previous scrutiny of the current evidence, we can now produce suggested guidelines for the practical implementation of extraction planning (assuming a full complement of healthy teeth). This section is a series of rules of thumb with supporting explanation and references. It is hoped that this provides a straightforward sequence of evidence-based thoughts which will produce a sensible extraction plan in the large majority of cases.

Plan the lower arch first This adage still seems very sensible as a way of a systematic thought process. However, it should be noted that factors relating to the upper incisors (such as the NLA) may strongly influence the planned A-P incisor position. Almost always, if we extract in the lower arch, there is some residual space to close. If the lower incisors are not to be retroclined (and this is rarely desired), then class 2 traction is required.

Assessing the lower arch crowding As discussed earlier, the factors which influence a target A-P position for the lower incisors should all be considered.

• A-P incisor stability – even though indefinite retention is planned • facial aesthetics

o profile o smile width

• achievement of a good occlusion • ease of achievement • long-term periodontal health

The amount of crowding is frequently a sufficiently strong factor to narrow the choice by itself to one of two lower extraction patterns in many cases.

The recommendations in Table 3.2 imply a differential anchorage effect between extraction of first or second premolars. This differential has long been assumed from the differential force theory, but is supported by a paper by Saelens and de Smit (1998) where the extraction of first premolars successfully accommodated twice the crowding than did the extraction of second premolars. The average lower incisor anteroposterior change was the same in both groups (0 mm) and the molars moved mesially 1 mm more in the second premolar extraction group. This convincing evidence is supported by the paper by Ong and Woods (2001) which clearly showed more

anchorage is provided in the upper arch by extraction of 4s than by extraction of 5s. Creekmore (1997), reviewing this subject concludes that as a rule of thumb, extraction of first premolars provides approximately 66% of the space for aligning/retracting the anterior teeth, whereas extraction of second premolars provides approximately half of the space.

Other factors will significantly influence the choice of

Category Millimetres of crowding Extraction pattern Mild 1 to 4 mm Non-extraction or

second premolars

Moderate 5 to 8 mm First premolars or second premolars

Severe 9+ mm First premolars

Table 3.2: Common extraction patterns related to category of crowding. Other factors may significantly modify this starting point.

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extractions within each category.

• desired antero-posterior incisor position (factors listed above) • any planned canine expansion • canine angulation • curve of Spee

The effect on available space of antero-posterior expansion/retraction The ‘traditional’ rule of thumb is that 1 mm of labial movement will provide sufficient space for 2 mm of crowding (1mm on each side of the arch). This rule of thumb assumes a rectangular arch form. In fact, with a much more realistic parabolic archform, the situation is more complicated and in general the labial movement will need to be greater than 1 mm to produce 2 mm of space. The paper by Steyn et al (1996) demonstrates this and interestingly, also calculates the effect of different arch depths and widths on the anterior movement of incisors required to accommodate a given amount of crowding. In general, the wider the intercanine distance and the shallower the arch depth from the canines to the mid-incisor point, the greater the A-P expansion required to accommodate a given amount of crowding (or conversely the greater the A-P retraction of incisors for a given amount of interdental stripping) and in cases presenting a specific dilemma, inspection of the table in the paper by Steyn is recommended .

In a given instance, the labial movement of lower incisors in a non-extraction case is frequently greater than that required to accommodate the crowded teeth. This reflects the additional use of class 2 traction and the degree of control of lower incisor inclination with occlusal plane levelling. For example, in non-extraction cases Saelens and De Smit (1998) found that to accommodate crowding of only 4 mm required an average of 5 mm of labial movement of lower incisors and not the 2 mm which the rule of thumb would have estimated. It will be seen in the chapter on self-ligation that there may possibly be less incisor proclination and greater lateral arch expansion if light forces and self-ligating brackets are employed to align crowded arches, but this has yet to be supported by strong evidence.

The effect on available space of lateral expansion Lateral expansion has been found to have less effect on arch perimeter than A-P expansion. An interesting paper by Noroozi et al (2002), demonstrates the ability of an algorithm based on two measurements of arch width and two of arch length to predict the arch perimeter increase which will result for any given A-P or lateral expansion. These authors again find that A-P expansion is much more effective than lateral expansion in providing space. Their formula again predicts approximately 1mm of arch length gain for 1mm of incisor labial movement. This is half of the ‘rule of thumb’. In the lateral dimension, each mm of canine expansion gives 0.6 mm of space and each mm of second molar expansion gives 0.3 mm.

Key point: Because dental arches are far from rectangular, 1 mm of labial incisor movement gives approximately 1 mm of extra arch length, not 2 mm. i.e. more labial movement of incisors is required to accommodate crowding than you might think.

The amount of curve of Spee The historical rule of thumb for this factor was 1 mm of space required for every 1 mm depth of curve of Spee. This has been shown to be an excessive calculation of space required. Germane and Staggers (1992) found a non-linear relationship and a less than one to one ratio for curves shallower than 9 mm. A more recent study by Braun et al (1996) found an even smaller effect - namely that a very deep curve of 9 mm only requires 2 mm of additional space. The strong tendency for labial flaring of lower incisors associated with non-extraction levelling of curves of Spee is therefore mainly due to choices in the biomechanics employed rather than to the space requirements. This will be discussed further in the chapter on Managing Overbites and is also referred to in the section on bracket prescriptions in the chapter on The Development of Preadjusted Appliance Systems.

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If the lower arch is non extraction:- Then non-extraction is our treatment of choice in the upper arch. If the case is suitable for functional appliance treatment then this is our preferred option if class 2 correction is required. If the upper second molars have erupted, the upper third molars are present and of good size and at least half a unit of distal movement is proposed, then the extraction of upper second molars can be considered. Waters (2001) has reported that this achieved 1.2 mm additional distal movement of the upper first molar and 5 degrees less incisor proclination, but this should be weighed against the long -term disadvantage of having a smaller more conically rooted third molar in place of a second molar. We almost never extract upper or lower second molars. (One exception is when intruding molars with TADS in the presence of unerupted 8s).

Although non-extraction is our treatment of choice if the lower arch is non-extraction, extraction of upper first premolars is much less demanding on anchorage and the occlusal disadvantages of a class 2 molar relationship are slight (see Andrews 1989: Straight Wire: The Concept And Appliance pages 182-187). If the initial molar relationship is more than half a unit class 2 and the case is not ideal for functional appliances, we would usually advocate extraction of upper first premolars. This does carry an increased chance of small residual spaces in the extraction sites. This is due partly to the difference in mesiodistal width between two premolars and one first molar and partly to the second premolars being teeth that are more frequently disproportionately small. This was discussed in the chapter on Occlusal Treatment Goals. Such occlusal imperfections may be considered much more acceptable than the consequences of insufficient anchorage to correct a class 2 relationship. A recent new factor in this decision between aiming for a class 1 or class 2 molar relationship is our ability to distalise buccal segments with miniscrews (See chapter on Temporary Anchorage Devices in Orthodontics)

If lower premolars are extracted:- Then upper premolars are almost always extracted. If the upper canines are at an ideal angulation or more distally angulated and must move distally by half a unit or more, then extraction of upper first premolars is recommended.

Therapeutic diagnosis Extractions are irreversible. Treatment response can be unpredictable. In a number of cases, it is sensible to start non-extraction and align the arches before making a decision on extraction. If extractions are then carried out, very little treatment time has been lost and the need for the extractions has been demonstrated to clinician and patient. The potentially different response to alignment with very gentle wires and self-ligating brackets has in our view increased the occasions when this approach is sensible. It is important to start such treatment with the clear understanding that if the clinician decides after some visits that extractions are required that this is a decision that must be implemented.

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Witzig JW and Spahl TJ (1987) The clinical outline of maxillofacial orthopaedic appliances 1st ed. Littleton, Mass: PSG Publishing: 167-216

Yang I-H, Nahm DS and Baek H-S (2008) Which hard and soft tissue factors relate with the amount of buccal corridor space during smiling? The Angle Orthodontist; 78: 5–11

Zierhut EC, Joondeph DR., Artun J and Little RM (2000) Long-term profile changes associated with successfully treated extraction and non-extraction Class II division I malocclusions. Angle Orthodontist 70: 208-219

Useful related references not referred to in this chapter

Proffitt WR (1994) Forty-year review of extraction frequencies at a University orthodontic department Angle Orthodontist 64: 407-413