The completion of a course of orthodontic treatment is followed by a stabilisation phase, which is known as retention. The objective is to prevent relapse, which is loss of orthodontic correction and movement of the teeth from the ideal aesthetic and functional position. During orthodontic therapy, the periodontal ligaments stretch and reorganise to accommodate the movement of the socket and to make tooth movement possible. If the teeth are not stabilised in their socket, the fibres of the periodontal ligaments will contract and relapse will occur. Relapse is multifactorial. Some contributing factors are continuous growth and muscular imbalances after active orthodontic treatment has ceased. Failing to eliminate the aetiology of the initial malocclusion is associated with relapse as well; for example, persistent digit sucking after completion of an orthodontic treatment will result in recurrence of an open bite. Studies prove that long‐term retention is beneficial for patients and reduces post‐treatment relapse. Over the years, there have been several interpretations of relapse and retention. Some commonly used retentions are discussed in this chapter, although retention is customised for each individual by the orthodontist and can greatly vary.
Importance of Retention
Retention is necessary for the following reasons:
- to allow newly formed bone (osteoid) to mature
- allow gingival fibres and periodontal ligaments to reorganise and adapt to the new arrangements
- neuromuscular adaptation
- to reduce the negative effects of continuous growth on the new occlusion to a degree
- to enhance the stability of orthodontic correction after completion of active treatment.
Orthodontists plan retention during the initial stages of treatment and discuss it with the patient before treatment starts. As with orthodontic treatment, the decision on the type and duration of retention varies among orthodontists. The type of retention planned is highly dependent upon growth, periodontal health, the initial malocclusion, the type of treatment and the condition of the soft tissues. It can take up to six months for the periodontal ligaments to reorganise and adapt to the new position and secure the tooth in the newly positioned socket (Mitchell, 2001). It also takes up to six months for the collagenous fibres in the gingiva to reorganise. However, some gingival fibres, such as the elastic supracrestal fibres, have a prolonged reorganisation time, which can take up to 12 months after removal of appliances. Therefore, retention is indicated for at least six months or longer post treatment. Studies prove that circumferential supracrestal fiberotomy a few weeks before removal of appliances can prevent significant relapse. This is particularly effective in cases of severe rotation.
Once phase I treatment is completed during mixed dentition, retention is recommended until the permanent dentition is established. Permanent retention is critical for prevention of relapse in poor periodontal conditions, as teeth will drift. It may be difficult to guarantee the permanence of the orthodontic correction for every treatment; however, orthodontists consider several factors and carefully plan retention to achieve as much stability of the end results as possible.
Fixed retainers are micromechanically bonded flexible multistranded wires or rigid stainless steel wires across the palatal and lingual surfaces of the anterior teeth (Figure 10.1). In some cases, buccal fixed retainers can be used and these are more commonly used in the posterior region for better aesthetics. The rigid stainless steel is only secured at either end on the canines to ensure that it is passive. Active fixed retainers induce unwanted tooth movement. This type of retention is widely used after completion of a course of phase I and phase II fixed orthodontic therapy.
Generally, fixed retainers can be left in place permanently to avoid any post‐treatment relapse. Fixed retainers cause minimal or no discomfort for the patient. Once the orthodontist confirms the ideal root and crown position on the final radiographs, upper and lower impressions or digital scans of the teeth are required for fabrication of fixed retainers. Even if one arch requires a fixed retainer, upper and lower impressions are needed as laboratory technicians need both arches for articulation of the plaster models to make sure the fabricated fixed retainers do not cause premature contacts.
These fixed retainers can make oral hygiene and maintenance difficult and impact interproximal cleaning or flossing. Patients must be advised to use super floss to achieve adequate interproximal cleaning.
Bonding Fixed Retainers
Steps involved in bonding fixed lingual or palatal retainers are shown in Box 10.1.