An Introduction to Orthodontics, 2nd Edition

1. The rationale for orthodontic treatment



Orthodontics is that branch of dentistry concerned with facial growth, with development of the dentition and occlusion, and with the diagnosis, interception, and treatment of occlusal anomalies.


Numerous surveys have been conducted to investigate the prevalence of malocclusion. It should be remembered that the figures for a particular occlusal feature or dental anomaly will depend upon the size and composition of the group studied (for example age and racial characteristics), the criteria used for assessment, and the methods used by the examiners (for example whether radiographs were employed).

Table 1.1 UK Child Dental Health Survey 1993

In the 12-year-old age band:

Crowding sufficient to impede/prevent eruption


Overjet >5 mm


At least one instanding incisor


It has been estimated that approximately 66 per cent of 12-year-olds in the UK require some form of orthodontic intervention, and around 33 per cent need complex treatment. In addition, now that a greater proportion of the population are keeping their teeth for longer, orthodontic treatment has an increasing adjunctive role prior to restorative work.


It is perhaps pertinent to begin this section by reminding the reader that malocclusion is one end of the spectrum of normal variation and is not a disease.

Ethically, no treatment should be embarked upon unless a demonstrable benefit to the patient is feasible. In addition, the potential advantages should be viewed in the light of possible risks and side-effects, including failure to achieve the aims of treatment. Appraisal of these factors is called riskbenefit analysis and, as in all branches of medicine and dentistry, needs to be considered before treatment is embarked upon for an individual patient. In parallel, financial constraints coupled with the increasing costs of health care have led to an an increased focus upon the costbenefit ratio of treatment. Obviously the threshold for treatment and the amount of orthodontic intervention will differ between a system that is primarily funded by the state and one that is private or based on insurance schemes.

The decision to embark upon a course of treatment will be influenced by the perceived benefits to the patient in terms of improved function and aesthetics, balanced against the risks of appliance therapy and the prognosis for achieving the aims of treatment successfully. In this chapter we consider each of these areas in turn, starting with the results of research into the possible benefits of orthodontic treatment upon dental health and psychological well-being.

1.3.1. Dental health


Research has failed to demonstrate a significant association between malocclusion and caries, whereas diet and the use of fluoride toothpaste are correlated with caries experience. However, clinical experience suggests that in susceptible children with a poor diet, malalignment may reduce the potential for natural tooth-cleansing and increase the risk of decay.

Periodontal disease

The association between malocclusion and periodontal disease is weak, as research has shown that individual motivation has more impact than tooth alignment upon effective tooth brushing. Certainly, in the partially edentulous mouth the last remaining teeth are usually the lower incisors an area which is commonly associated with crowding. Nevertheless, certain occlusal anomalies may prejudice periodontal support.

Crowding may lead to one or more teeth being squeezed buccally or lingually out of their investing bone, resulting in a reduction of periodontal support. This may also occur in a Class III malocclusion where the lower incisors in cross-bite are pushed labially, leading to gingival recession. Traumatic overbites can also lead to increased loss of periodontal suppport and therefore are another indication for orthodontic intervention.

Finally, an increased dental awareness has been noted in patients following orthodontic treatment, and this may be of long-term benefit to oral health.

Trauma to the anterior teeth

The risk of trauma to the upper incisors increases with the size of the overjet. The 1983 Child Dental Health Survey found that children with overjets in excess of 9 mm were twice as likely to experience trauma. Boys and patients with incompetent lips appear to be more at risk; however, the prevalence of trauma reduces with age, with the peak incidence occurring around 10 years.

Masticatory function

Patients with anterior open bites and those with markedly increased or reverse overjets often complain of difficulty with eating, particularly when incising food.


The soft tissues show remarkable adaptation to the changes that occur during the transition between the primary and mixed dentitions, and when the incisors have been lost owing to trauma or disease. In the main, speech is little affected by malocclusion, and correction of an occlusal anomaly has little effect upon abnormal speech. However, if a patient cannot attain contact between the incisors anteriorally, this may contribute to the production of a lisp (interdental sigmatism).

Tooth impaction

Unerupted teeth may rarely cause pathology. Unerupted impacted teeth, for example maxillary canines, may cause resorption of the roots of adjacent teeth. Dentigerous cyst formation can occur around unerupted third molars or canine teeth. Supernumerary teeth may also give rise to problems, most importantly where their presence prevents normal eruption of an associated permanent tooth or teeth.

Temporomandibular joint dysfunction syndrome

This topic is considered in more detail in Section 1.7, where the effects of both malocclusion and orthodontic treatment upon the temporomandibular joint and associated musculature are considered.

In summary, there are a number of dental traits which do appear to have an adverse effect upon the longevity of the dentition, indicating that their correction would benefit long-term dental health. These include the following:

·     Increased overjet

·     Increased traumatic overbites

·     Anterior crossbites (causing a decrease in labial periodontal support of affected lower incisors)

·     Unerupted impacted teeth (where there is a danger of pathology).

·     Crossbites associated with mandibular displacement.

1.3.2. Psychosocial well-being

While it is accepted that dentofacial anomalies and severe malocclusion do have a negative effect on the pyschological well-being and self-esteem of the individual, the impact of more minor occlusal problems is more variable and is modified by social and cultural factors. Research has shown that an unattractive dentofacial appearance does have a negative effect on the expectations of teachers and employers. However, in this respect, background facial appearance would appear to have more impact than dental appearance.

A patient's perceptions of the impact of dental variation upon his or her self-image is subject to enormous diversity and is modified by cultural and racial influences. This results in some individuals being unaware of marked malocclusions, whilst others complain bitterly about very minor irregularities.

The dental health component of the Index of Orthodontic Treatment Need was developed to try and quantify the impact of a particular malocclusion upon long-term dental health. The index also comprises an aesthetic element which is an attempt to quantify the aesthetic handicap that a particular arrangement of the teeth poses for a patient. Both aspects of this index are discussed in more detail in Chapter 2.


After working with the general public for a short period of time, it can readily be appreciated that demand for treatment does not necessarily reflect need for treatment. Some patients will complain bitterly about mild rotations of the upper incisors, whilst others are blithely unaware of markedly increased overjets. It has been demonstated that awareness of tooth alignment and malocclusion, and willingness to undergo orthodontic treatment, are greater in the following groups.

·     females

·     higher socio-economic families/groups

·     in areas which have a smaller population to orthodontist ratio, presumably because appliances become more accepted.

One interesting example of the latter has been observed in countries where provision of orthodontic treatment is mainly privately funded, for example, the USA, as orthodontic appliances are now perceived as a status symbol.

With the increasing dental awareness shown by the public and the increased acceptability of appliances, the demand for treatment is increasing rapidly, particularly among the adult population who may not have had ready access to orthodontic treatment as children. In addition, increased dental awareness also means that patients are seeking a higher standard of treatment result. These combined pressures place considerable strain upon the limited resources of state-funded systems of care. As it appears likely that the demand for treatment will contine to escalate, some form of rationing of state-funded treatment is inevitable and is already operating in some countries. In Sweden for example, the contribution made by the state towards the cost of treatment is based upon need for treatment as determined by the Swedish Health Board's Index.


Like any other branch of medicine or dentistry, orthodontic treatment is not without potential risks (see Table 1.2).

Table 1.2 Potential risks of orthodontic treatment


Avoidance/Management of risk


Dietary advice, improve oral hygiene, increase availablity of fluoride
Abandon treatment

Periodontal attachment loss

Improve oral hygiene

Root resorption

Avoid treatment in patients with resorbed, blunted, or tapered roots

Loss of vitality

If history of previous trauma to incisors, counsel patient

1.5.1. Root resorption

It is now accepted that some root resorption is inevitable as a consequence of tooth movement. During the course of a conventional two-year fixed-appliance treatment around 1 mm of root length will be lost on average. However, this mean masks a wide range of individual variation, as some patients appear to be more susceptible and undergo more marked root resorption. Radiographic signs which indicate an increased susceptibility include shortened roots with evidence of previous root resorption, pipette-shaped or blunted roots, and teeth which have previously suffered an episode of trauma. In addition, more marked resorption is seen in cases where extensive movement of root apices has been undertaken.

1.5.2. Loss of periodontal support

As a result of reduced access for cleansing, an increase in gingival inflammation is commonly seen following the placement of fixed appliances. This normally reduces or resolves following removal of the appliance, but some apical migration of periodontal attachment and alveolar bony support is usual during a two-year course of orthodontic treatment. In most individuals this is minimal, but if oral hygiene is poor, more marked loss may occur.

Removable appliances may also be associated with gingival inflammation, particularly of the palatal tissues, in the presence of poor oral hygiene.

1.5.3. Decalcification

Caries or decalcification occurs when a cariogenic plaque occurs in association with a high-sugar diet. The presence of a fixed appliance predisposes to plaque accumulation as tooth cleaning around the components of the appliance is more difficult. Decalcification during treatment with fixed appliances is a real risk, with a reported prevalence of between 2 and 96 per cent (see Chapter 17, Section 17.7).

1.5.4. Soft tissue damage

Traumatic ulceration can occur during treatment with both fixed and removable appliances, although it is more commonly seen in association with the former as a removable appliance which is uncomfortable is usually removed. Over-enthusiastic apical movement, can lead to a reduction in blood supply to the pulp and even pulpal death. Teeth which have undergone a previous episode of trauma appear to be particularly susceptible, probably because the pulpal tissues are already compromised.

Temporomandibular joint dysfunction syndrome

This is discussed in Section 1.7.


The decision to embark upon orthodontic treatment must also consider the effectiveness of appliance therapy in correcting the malocclusion of the individual concerned. This has several aspects.

·     Are the tooth movements planned attainable? This is considered in more detail in the chapter on treatment planning but, in brief, tooth movement is only feasible within the constraints of the skeletal and growth patterns of the individual patient. The wrong treatment plan, or failure to anticipate adverse growth changes, will reduce the chances of success. In addition, the probable stablility of the completed treatment needs to be considered. If a stable result is not possible, do the benefits conferred by proceeding justify prolonged retention, or the possibility of relapse?

·     There is a wealth of evidence to show that orthodontic treatment is more likely to achieve a pleasing and successful result if fixed rather than removable appliances are used, and if the operator has had some postgraduate training in orthodontics.

·     Patient co-operation.

The likelihood that orthodontic treatment will benefit a patient is increased if the malocclusion is severe and appliance therapy is planned and carried out by an experienced orthodontist. The likelihood of gain is reduced if the malocclusion is mild and treatment is undertaken by an inexperienced operator.

In essence, it may be better not to embark on treatment at all, rather than run the risk of failing to achieve a worthwhile improvement.

Table 1.3 Failure to achieve treatment objectives

Operator factors

Patient factors

Errors of diagnosis

Poor oral hygiene

Errors of treatment planning

Failure to wear appliances

Anchorage loss

Failed appointments

Technique errors


The aetiology and management of temporomandibular pain dysfunction syndrome (TMPDS) have aroused considerable controversy in all branches of dentistry. The debate has been particularly heated regarding the role of orthodontics, with some authors claiming that orthodontic treatment can cause TMPDS, whilst at the same time others have advocated appliance therapy in the management of the condition.

There are a number of factors that have contributed to the confusion surrounding TMPDS. The objective view is that TMPDS is of multifactorial aetiology, with psychological, traumatic, and occlusal factors all being implicated. Of these, stress is probably the most important, with its effect being mediated by para-functional activity, for example bruxism, which causes muscle pain and spasm. Success has been claimed for a wide assortment of treatment modalities, reflecting both the multifactorial aetiology and the self-limiting nature of the condition. Apart from internal derangement of the joint, the symptoms of TMPDS usually respond to any treatment which helps to reduce abnormal parafunctional muscle activity.

1.7.1. Orthodontic treatment as a contributory factor in TMPDS

A survey of the literature reveals that those articles claiming that orthodontic treatment (with or without extractions) can contribute to the development of TMPDS are predominantly of the viewpoint (based on the authors opinion) and case report type. In contrast, controlled longitudinal studies have indicated a trend towards a lower incidence of the symptoms of TMPDS among post-orthodontic patients compared with matched groups of untreated patients.

The consensus view is that orthodontic treatment, either alone or in combination with extractions, does not cause TMPDS.

1.7.2. The role of orthodontic treatment in the prevention and management of TMPDS

Some authors maintain that minor occlusal imperfections lead to abnormal paths of closure and/or bruxism, which then result in the development of TMPDS. If this were the case, then given the high incidence of malocclusion in the population (5075 per cent), one would expect a higher prevalence of TMPDS than the reported 530 per cent. A number of carefully controlled longitudinal studies have been carried out in the USA, and these have found no relationship between the signs and symptoms of TMPDS and the presence of non-functional occlusal contacts or mandibular displacements. However, other studies have found a small but statistically significant association between TMPDS and crossbites, anterior open bite and Class III malocclusions. It is important to remember the multifactorial nature of TMPDS perhaps, the presence of a displacing contact in susceptible individuals contact may act as the focus of a parafunctional habit mediated by stress.


American Journal of Orthodontics and Dentofacial Orthopedics101 (1) (1992).

This is a special issue dedicated to the results of several studies set up by the American Association of Orthodontists to investigate the link between orthodontic treatment and the temporomandibular joint. It is essential reading for all those involved in dentistry.

Harris, M., Feinmann, C., Wise, M., and Treasure, F. (1993). Temporomandibular joint and orofacial pain: clinical and medicolegal management problems.British Dental Journal174, 12936.

Discusses the role of psychogenic factors in the aetiology of TMPDS.

Holmes, A. (1992). The subjective need and demand for orthodontic treatment. British Journal of Orthodontics19, 28797.

Luther, F. (1998). Orthodontics and the TMJ: Where are we now? Angle Orthodontist68, 295318.

An authoritative review of the literature on this subject.

Murray, A. M. (1989). Discontinuation of orthodontic treatment: a study of the contributing factors. British Journal of Orthodontics16, 17.

Office of Population Censuses and Surveys (1994). Children's dental health in the United Kingdom 1993. HMSO, London.

Richmond, S. (1993). The provision of orthodontic care in the general dental services of England and Wales: extraction patterns, treatment duration, appliance types and standards. British Journal of Orthodontics20, 34550.

Salonen, L., Mohlin, B., Götzlinger, B., and Helldén, L. (1992). Need and demand for orthodontic treatment in an adult Swedish population. European Journal of Orthodontics14, 35968.

Shaw, W. C., OBrien, K. D., Richmond, S. and Brook, P. (1991). Quality control in orthodontics: risk/benefit considerations. British Dental Journal170, 337.

A rather pessimistic view of orthodontics.

Tang, E. L. K. and Wei, S. H. Y. (1990) Assessing treatment effectiveness of removable and fixed orthodontic appliances with the occlusal index. American Journal of Orthodontics and Dentofacial Orthopedics99, 5506.

The authors concluded that the effectiveness of fixed appliances (as measured with the occlusal index) is much greater than that of removable appliances.

Turbill, E. A., Richmond, S., and Wright, J. L. (1999). A closer look at GDS orthodontics in England and Wales 1: Factors influencing effectiveness. British Dental Journal187, 21116.

Wassell, R. W. (1989) Do occlusal factors play a part in temporomandibular dysfunction? Journal of Dentistry17, 10110.

The restorative viewpoint.


Wheeler, T. T. McGorray, S. P., Yurkiewicz, L., Keeling, S. D., and King, G. J. (1994) Orthodontic treatment demand and need in third and fourth grade schoolchildren. American Journal of Orthodontics and Dentofacial Orthopedics106, 2233.

Contains a good discussion on the need and demand for treatment.



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