12 Adult orthodontics

An increasing number of adults are undergoing orthodontic treatment and this is a global trend. Adult dental health has improved significantly over the past few decades in the UK, with more teeth being retained for longer in this population. This has been accompanied by an increasing preoccupation with personal appearance and in particular, the importance of an attractive smile. As a result of the media and increasing use of the Internet, adults are more aware of the aesthetic improvements that can be achieved with orthodontic treatment and it has become more socially acceptable for them to wear fixed orthodontic appliances. Improvements in socioeconomic status and personal wealth have meant that the finances are increasingly available for them to seek out and embark on such treatment.

Why do adults undertake orthodontic treatment?

An adult may be motivated primarily by a desire to improve their dental appearance and may request orthodontic treatment. Amongst this group will be those who either refused or were not given the opportunity of treatment during their childhood, and those who may have received treatment but have been left dissatisfied with the result, often because of subsequent relapse or an inappropriate original treatment plan (Fig. 12.1). Routine orthodontics can be readily carried out in these patients, but the scope of increasingly complex treatment can be more limited in comparison to that which might be achieved in a growing child or adolescent. Moreover, adults can also present with other age-related problems that must be considered when providing orthodontic treatment (Box 12.1).

Figure 12.1 This adult patient was unhappy with the appearance of their teeth.

Orthodontic treatment as a child had involved the loss of four premolars and fixed appliances to correct their class II division 1 malocclusion. Unfortunately, the incisor relationship was not fully corrected, which left a residual overjet that has almost certainly worsened. In addition, there has also been relapse in the incisor alignment within both dental arches (upper panels). Definitive treatment as an adult involved fixed appliances and bimaxillary surgery to correct the underlying skeletal discrepancy and produce a well-aligned class I occlusion (lower panels).

Box 12.1 Special problems associated with orthodontic treatment in adults

A number of features associated with adult patients can make orthodontic treatment more challenging and these all need to be taken into consideration when planning and embarking upon treatment (Nattrass & Sandy, 1995).

Growth

Adults are non-growing individuals which will reduce the scope of treatment available in comparison to that for a child or adolescent.

• Growth modification is not possible: a skeletal discrepancy will have to be either accepted or corrected with surgery.

• A lack of vertical condylar growth makes overbite correction more challenging. To avoid an increase in the vertical dimension, tooth intrusion is required and this is difficult (see Fig. 11.13).

• The midpalatal suture is essentially closed, which precludes any skeletal expansion of the maxillary arch without surgery.

Periodontal Tissues

The prevalence of periodontal disease and loss of attachment increases with age, becoming more common in adults. An adult patient should undergo a complete clinical and radiographic assessment of their periodontal status before embarking on orthodontic treatment (Johal & Ide, 1999). Previous attachment loss does not preclude orthodontics, but active periodontal disease will require treatment and evidence of stabilization before any appliances are placed (Table 12.1). An excellent standard of plaque control should be attained and then maintained throughout treatment, if necessary with professional supra- and subgingival scaling. Teeth with previous attachment loss and reduced bony support will also respond differently to orthodontic force:

• The centre of resistance moves apically (see Fig. 5.4) and tipping occurs more readily than bodily movement; and

• The relative anchorage value will reduce.

Increasing age is associated with a reduction in vascularization and collagen turnover within the periodontium, with an overall reduction in bone volume. Initial tooth movement can be slower in adults and light forces should be used to avoid the risk of root resorption.

Restorations

Adult patients often have a heavily restored dentition, which can complicate the choice of orthodontic extractions and necessitate the bonding of appliances to ceramics or alloys. Root canal-treated teeth are amenable to orthodontic tooth movement as long as they are symptomless and correctly obturated (Drysdale et al, 1996).

Aesthetics

Whilst adult patients will accept fixed orthodontic appliances, they often request aesthetic tooth-coloured brackets, which can produce wear of opposing teeth, enamel fractures on debonding and increased friction. Lingual fixed appliances or transparent removable appliances can also be used, but these can represent a compromise in terms of efficient tooth movement.

Alternatively, orthodontic treatment may not be sought directly by an adult, but prescribed as one component of a specific treatment plan:

• To facilitate restorative or periodontal treatment;

• For surgical correction of a jaw discrepancy to optimize the proposed surgical movements and ensure a stable and functional postsurgical occlusion;

• To use intraoral mandibular advancement appliances as part of a non-surgical treatment regime in the treatment of obstructive sleep apnoea.

Orthodontics as an adjunct to restorative treatment

Adults can often present with an incomplete dentition, permanent teeth having been lost prematurely as a result of caries, periodontal disease or trauma. This can lead to alterations in position of the remaining teeth due to drifting, tipping, rotation or overeruption (Fig. 12.2). Whilst there are obvious negative aesthetic consequences associated with tooth loss and alterations in the position of adjacent teeth, occlusal instability and functional problems can also occur and contribute to:

• Excessive tooth wear;

• Pulpal involvement, loss of vitality and periodontal destruction associated with teeth in traumatic occlusion; and

• Temporomandibular dysfunction.

Figure 12.2 Tooth migration and tipping in adult dentitions compromised by tooth extraction.

In the oral rehabilitation of adult patients affected by tooth loss, orthodontic treatment may be required as part of their multidisciplinary management in a variety of situations:

• Space closure to improve aesthetics and obviate the need for restorative treatment;

• Uprighting of abutment teeth to remove occlusal interferences or provide space for an adjacent restoration (Fig. 12.3);

• Intrusion of overerupted teeth to remove occlusal interferences or provide space in the opposing arch for the placement of a restoration;

• Extrusion of teeth to increase crown length and allow coronal restoration; and

• Simple alignment to remove occlusal interferences or permit coronal restoration.

Figure 12.3 An adult patient with a congenitally absent UL2 was unhappy with the aesthetics of a resin-retained bridge bonded to the UL1 and UL3.

The UL3 was markedly distally angulated, which precluded the placement of an implant restoration for the UL2. Following removal of the bridge pontic, orthodontic treatment was carried out to upright the UL3 and create space for an implant.

In many cases, adjunctive orthodontic treatment of this kind will not attempt definitive correction of a malocclusion; rather it will be restricted to moving only those teeth required for the specific treatment plan.

Orthodontics as an adjunct to periodontal treatment

Tooth migration can also occur as a consequence of attachment loss secondary to periodontal disease. In particular, the labial segments can procline significantly, resulting in an increased overjet, generalized spacing and extrusion with lengthening of the clinical crowns (Fig. 12.4). Orthodontic treatment can be carried out to retract or intrude these teeth and close spaces, but permanent retention is usually required to maintain the new position. Orthodontic intrusion can also reduce the clinical crown height and improve attachment levels if light forces are employed and associated with minimal tipping (Melsen, 2001). A prerequisite before embarking upon any orthodontic treatment in the periodontally compromised patient is stabilization of the disease process itself (Table 12.1).

Figure 12.4 Rotation and extrusion of the UL1 as a result of periodontal disease.

The position of the UL1 was corrected with fixed appliances and permanent retention.

Table 12.1 Treatment targets in patients with active periodontal disease prior to embarking on orthodontic treatment ^a

• Smokers should stop the habit;

• Pocket reduction of 1 mm for those of depth 4–6 mm;

• Pocket reduction of 2 mm or more for those of depth > 6 mm;

• Bleeding and plaque scores less than 15%;

• Cleanable teeth and prostheses; and

• No root caries.

a Johal & Ide (1999).

Orthodontics and orthognathic surgery

A malocclusion associated with any significant discrepancy in the dentofacial skeleton of an adult requires a combination of orthodontics and surgical repositioning of the jaws for definitive correction (Fig. 12.5). These skeletal problems can include:

• Anteroposterior disproportion associated with the size or position of the maxilla and mandible in class II and class III cases;

• Vertical disproportion, associated with excessive or reduced maxillary incisor tooth show, increased overbite or open bite;

• Transverse anomalies; and

• Asymmetries of the face and jaws.

Figure 12.5 Severe class II (upper) and class III (lower) malocclusion.

Orthodontic camouflage may be possible in some cases, but this approach can be a compromise and limited by the extent of the skeletal discrepancy. Growth modification is not possible in an adult, but many of these malocclusions would be amenable to attempts at treatment with a functional appliance if diagnosed in a growing child or adolescent. However, it should be remembered that these more severe forms of skeletal discrepancy are the ones least likely to respond to attempts at growth modification and often end up requiring a surgical approach.

Orthognathic surgery can involve a range of surgical movements, which achieve repositioning of the maxilla or mandible within the facial skeleton (Fig. 12.6). Surgery of this kind does not affect any inherent growth capacity that may reside in the jaws and for this reason it is only carried out once skeletal growth has ceased, in the adult. This is particularly important for class III cases with mandibular excess, where continued forward growth of the mandible after backward surgical repositioning can lead to the reappearance of a reverse overjet if the surgery is carried out before growth has ceased.