As dental awareness is growing and orthodontic appliances are now becoming more socially acceptable, a increasing number of adult patients are seeking orthodontic treatment. At the same time, a greater proportion of the general public are keeping their teeth for longer, which is resulting in an increasing demand for orthodontic treatment to facilitate restorative and periodontal care.
19.1. DIFFICULTIES POSED BY ORTHODONTIC TREATMENT FOR ADULTS
Orthodontic treatment is usually carried out in children around the time of the pubertal growth spurt and/or soon after eruption of the permanent dentition. Both spontaneous and dynamic tooth movement are accomplished more readily at this age, and active growth facilitates the correction of skeletal discrepancies. In contrast, if orthodontic treatment is delayed until adulthood treatment may be complicated by the following:
Negligible growth Although recent studies indicate that growth does continue throughout adulthood, this is at a much diminished rate compared with childhood. This means that the threshold for surgery is lower in adult patients with skeletal discrepancies or increased overbite.
Reduced tissue blood supply and cell turnover As a result the response to orthodontic force is more sluggish (in children the initial reaction to orthodontic force occurs within 24 hours, whereas in adults it can take up to 3 weeks) and tissue reorganization following tooth movement takes longer.
Reduced periodontal attachment The incidence and severity of periodontal attachment loss increases with age, and the load upon a reduced periodontium can be further exacerbated by tooth loss. In some cases the teeth are less able to resist soft tissue and occlusal forces, leading to migration and drifting of particularly the incisors. Where orthodontic treatment is planned for teeth with reduced periodontal support, the forces applied to the teeth need to be decreased accordingly, and patients with gingival recession should be counselled that orthodontic treatment may accelerate this problem.
Missing and heavily restored teeth Tooth loss may lead to migration and/or tilting of the adjacent teeth and to over-eruption of the opposing teeth, thus contributing to disruption of the occlusion. In addition, atrophy of the alveolar bone following extraction can lead to ‘necking’ (Fig. 19.1). Inadequate restorations with poor contact points, deficient occlusal stops, or premature contacts may also lead to occlusal disharmonies and/or mandibular displacement. The choice of teeth for extraction in adults is often determined by the prognosis of individual teeth.
Adults are less able to adapt to discrepancies in the occlusion Therefore even more care is required to ensure that a good functional occlusion is achieved at the end of treatment.
19.2. PRACTICAL ORTHODONTIC MANAGEMENT IN ADULTS
A thorough orthodontic assessment (Chapter 5) should be carried out prior to planning treatment, and this should include a careful examination of the condition of the teeth, both periodontally and restoratively. In some adults this may involve taking full-mouth radiographs. If the patient has several missing teeth it is important to observe the path of closure of the mandible on the hinge axis, looking particularly for displacements. As with children, good dental care is a prerequisite to orthodontic treatment, but in the adult it is even more important that any periodontal disease is controlled before orthodontic appliances are placed. In many adult patients assessment and treatment planning should be carried out jointly with other disciplines, particularly if periodontal disease is present and/or restorative work is necessary.
Management of Class I, Class II, and Class III malocclusions in the adult will generally run along the lines discussed in Chapters 8, 9, 10, 11. However, owing to the lack of growth there is a lower threshold for surgery in the management of skeletal discrepancies and increased overbite. Treatment planning in the adult, including anchorage requirements, may be compromised by previous tooth loss and the condition of the remaining teeth, and in some cases a compromise may have to be accepted as a result.
Where possible, overbite reduction should be achieved by intrusion, as extrusion of the molars tends to relapse once appliances are removed. On occasion, limited crown reduction can be considered when over-eruption has occurred. Rarely, this may involve elective devitalization to prevent pulpal problems, followed by crowning when treatment is complete. Alternatively, surgery may be required.
Lighter forces should be used in the adult, particularly initially and where periodontal support is reduced. A slower rate of tooth movement can be expected in the older patient, particularly initially. Spontaneous tooth movement and space closure is also much reduced in the adult dentition. Distal movement of the upper buccal segments is not really an option in the mature dentition, although extraoral anchorage can be used provided that the patient is prepared to accept it. Despite the increased acceptance of orthodontics, adult patients are usually keen for appliances to be as unobtrusive as possible. Tooth-coloured brackets (Fig. 19.2) lingual or minibrackets can be used, and these improve the aesthetics of a fixed appliance. Crowned or heavily restored teeth often pose a problem for bonded attachments. Silane coupling agents can be used in conjunction with a composite orthodontic adhesive for bonding to porcelain veneers or crowns, but the retention rates are often disappointing. If much of the labial surface is involved in a metal restoration, there may be no alternative but to use a band around the tooth. Patients should be warned prior to starting treatment if there is a risk of a restoration being dislodged when the appliance is removed, and if complex restorative treatment is required this is often best delayed until after the orthodontic phase is complete.
Because of the slower rate of tissue reorganization, retention following orthodontic treatment in the adult may need to be prolonged or even permanent.
19.3. ORTHODONTICS AS AN ADJUNCT TO RESTORATIVE WORK
As the proportion of the population with some natural teeth increases, so does the need for joint management of adults with ‘mutilated’ dentitions due to tooth loss and periodontal disease. Where collaboration between orthodontist and
restorative dentist is required in the management of a case, it is preferable to see the patient jointly to formulate a integrated treatment plan. The following are examples of problems that benefit from a joint restorative–orthodontic approach:
Redistribution/closing of space Following unplanned tooth loss, space closure or movement of a proposed abutment tooth into the middle of an edentulous span may be indicated to facilitate fabrication of a durable prosthesis.
Uprighting of tilted bridge abutments If, following the loss of a permanent tooth, the adjacent teeth tilt into the space, replacement of the missing unit with bridgework may be complicated by a lack of parallelism of the abutment teeth. One possible option is to upright the adjacent teeth prior to bridgework.
Intrusion of over-erupted teeth Intrusion of over-erupted teeth may be required prior to restorative work in the opposing arch.
Extrusion of fractured teeth This is usually required where the fracture line extends below the gingival margin. Although extrusion brings the margin supragingivally and facilitates placement of a crown or restoration, it must be remembered that extrusion will also adversely affect the crown-to-root ratio.
Where a combined approach is indicated, it is often wise to allow a period of stabilization between the phases of treatment of differing specialities.
19.4. MIGRATION OF PERIODONTALLY INVOLVED INCISORS
Migration of periodontally compromised incisors is an increasingly common problem and therefore is considered separately in this section.
Patients with loss of periodontal attachment may experience labial drifting of the teeth, most commonly the upper incisors, although other teeth can be affected. This may be due to a number of factors, and one or more may be operating in an individual case:
Reduced bony support means that the teeth are less able to withstand adverse soft tissue and occlusal forces, and tooth movement occurs.
Periodontal inflammation leads to extrusion of the teeth, bringing them into traumatic occlusion. If the periodontal support is also reduced, the teeth may drift as a result (Fig. 19.3).
If a premature contact which results in a forward slide of the mandible on closure occurs in a patient with periodontally involved upper incisors, proclination of the upper labial segment may occur as a result.
Lack of posterior support due to tooth loss places undue pressures on the incisors, leading particularly to proclination of the upper incisors.
Initial management has to include stabilization of the periodontal condition and an assessment of the prognosis of the affected teeth. If the prognosis is satisfactory and orthodontic alignment is planned, the most difficult aspect is often over-bite reduction. If the overbite is not markedly increased, a removable bite-plane appliance can be used (Fig. 19.4), but it should be remembered that this will
lead to overbite reduction by extrusion of the molars which will tend to relapse post-treatment. Fixed appliances are required if incisor intrusion is indicated. However, there is a limit to the amount of overbite reduction that can be attempted, and either crown height reduction or surgery may be indicated.
If a forward slide from a premature contact is an aetiological factor, this should be eliminated to allow the patient to attain their true intercuspal position (centric relation). This often necessitates a course of splint therapy, which is best carried out by the restorative member of the team who can then advise on elimination of any premature contacts revealed by this process.
Reduction of the increased overjet is usually relatively straightforward with a fixed appliance in most cases (Fig. 19.5). However, permanent retention is usually necessary following treatment. This can most easily be accomplished with a conventional bonded retainer, although in some cases a metal splint (similar to the retention wings of an acid-etch retained bridge), attached to the palatal aspect of the teeth with composite, may be indicated to provide additional support to periodontally involved teeth (Fig. 19.6).
PRINCIPAL SOURCES AND FURTHER READING
Heasman, P. A. and Millett, D. T. (1996). The periodontium and orthodontics in health and disease. Oxford University Press, Oxford.
Howat, A. P. and Warren, K. (1991). A restorative–orthodontic approach in the older patient. British Journal of Orthodontics, 18, 195–201.
An interesting case report which illustrates the teamwork required in a combined periodontal–orthodontic–restorative treatment for a 60-year-old patient.
Kahl-Nieke, B. (1996). Retention and stability considerations for adult patients. Dental Clinics of North America, 40, 961–94.
Khan, R. S. and Horrocks, E. N. (1991). A study of adult orthodontic patients and their treatment. British Journal of Orthodontics, 18, 183–94.
Melsen, B., Agerbaek, N., Eriksen, J., and Terp, S. (1988). New attachment through periodontal treatment and orthodontic extrusion. American Journal of Orthodontics and Dentofacial Orthopedics, 94, 104–16.
A thought-provoking article.
Melsen, B., Agerbaek, N., and Markenstam, G. (1989). Intrusion of incisors in adult patients with marginal bone loss. American Journal of Orthodontics and Dentofacial Orthopedics, 96, 232–41.
Nattrass, C. and Sandy, J. R. (1995). Adult Orthodontics — a review. British Journal of Orthodontics, 22, 331–7.
Norton, I. A. (1988). The effect of ageing cellular mechanisms on tooth movement. Dental Clinics of North America, 32, 437–46.