CLINICAL GUIDELINES FOR ORTHODONTIC RETENTION

ORTHODONTIC RETENTION

1. INTRODUCTION

Retention is the phase of orthodontic treatment which maintains the teeth in their orthodontically corrected positions following the cessation of active orthodontic tooth movement. Orthodontic retainers resist the tendency of teeth to return to their pre-treatment positions under the influence of periodontal, occlusal and soft tissue forces, and continuing dentofacial growth. Very few prospective controlled studies have evaluated the effectiveness of retention

Retention is advisable for almost all treated malocclusions. A recent survey carried out in the UK found that the most commonly used retention period was 12 months. This approach is supported by histological studies which have shown that the supracrestal periodontal fibres remain stretched and displaced for more than 7 months after the cessation of orthodontic tooth movement, suggesting that the retention period should generally be at least 7 months. However, individual patient factors can often modify the length of the retention phase.

2. OCCLUSAL AND OTHER FACTORS WHICH MAY MODIFY THE RETENTION PROTOCOL

2.1 Lower incisor alignment

Increases in lower incisor irregularity occur throughout life in a large proportion of patients following orthodontic treatment and also in untreated subjects. Recent evidence suggests that most change will take place by the middle of the third decade. It has been suggested that prolonged retention of the lower labial segment until the end of facial growth may reduce the severity of lower incisor crowding.

Patients’ expectations of the stability of their lower incisor alignment should be considered on completion of orthodontic treatment. If an individual is unwilling to accept any deterioration in lower incisor alignment following orthodontic treatment then permanent fixed or removable retention may have to be considered.

2.2 Corrected rotations of anterior teeth

As the supracrestal gingival fibres are known to take the longest amount of time to reorganise, prolonged retention of corrected rotations may be helpful in reducing relapse. While the use of adjunctive circumferential supracrestal fiberotomy has been shown to be effective in reducing relapse within the first 4-6 years after debonding, the additional long term clinical benefit from the procedure is relatively small.

2.3 Changes in the antero-posterior lower incisor position

Any intentional or non-intentional change of more than 2mm indicates the need for long-term or indefinite retention.

2.4 Correction of deep overbite

Following the correction of a very deep overbite, the use of an anterior biteplane until the completion of facial growth has been recommended. This may be particularly useful when there is evidence of an anterior mandibular growth rotation.

2.5 Correction of anterior open bites

While the use of retainers incorporating posterior biteblocks has been recommended for prolonged retention of anterior open bite malocclusions with unfavourable growth patterns, there is currently a lack of scientific evidence to support this.

2.6 Patients with a history of periodontal disease or root resorption

In patients with previously treated severe periodontal disease, permanent retention is advised. For those with minimum to moderate disease, a more routine retention protocol can be used. There is evidence of an increased risk of deterioration of lower incisor alignment post-retention in cases with root resorption or crestal bone loss.  These cases may therefore benefit from prolonged retention.

2.7 Growth modification treatment

Following the use of headgear or functional appliances, retention using a modified activator appliance has been reported as effective in maintaining Class II correction.  However, no comparative studies have confirmed the usefulness of this form of retention.

2.8 Correction of posterior and anterior crossbites

When the incisor overbite and posterior intercuspation are adequate for maintaining the correction, no retention is necessary.

2.9 Adult Patients

When the periodontal supporting tissues are normal and no occlusal settling is required, there is no evidence to support any changes in retention protocol for adult patients compared with adolescent patients.

2.10 Spaced dentitions 

 Permanent retention has been recommended following orthodontic treatment to close generalised spacing or a midline diastema in an otherwise normal occlusion.

3. RETAINER DESIGN

3.1 Removable retainers with a labial bow (Hawley and Begg type retainers)

These retainers are robust and can be worn during eating. Hawley retainers have been recently shown to have the advantage of facilitating posterior occlusal settling in the initial three months of retention.The labial bow can be used to accomplish simple tooth movements if required, and an anterior biteplane can easily be incorporated for retention of a corrected deep overbite.

3.2 Removable vacuum formed retainers 

  
Vacuum formed retainers are relatively inexpensive and can be quickly fabricated on the same day as appliance removal. They are discreet and can be modified to produce tooth movements if required. Full posterior occlusal coverage (including second molars if present) is advisable in order to reduce the risk of over eruption of these teeth during retention.

Recent research has shown that vacuum formed retainers were significantly less effective in promoting posterior occlusal settling than Hawley retainers.  However this is likely to be of little importance if good posterior intercuspation has been established by the time of debonding.

3.3 Fixed bonded retainers (Smooth wire, Flexible spiral wire)

  
Fixed retainers are indicated for long-term retention of the labial segments, particularly when there is reduced periodontal support, and for retention of a midline diastema.  Fixed retainers are discreet and reduce the demands on patient compliance. However they are associated with failure rates of up to 47%, particularly on upper incisors when there is a deep overbite. In addition, calculus and plaque deposition is greater than with removable retainers. Fixed retainers therefore require long term maintenance.

Flexible spiral wire retainers allow differential tooth movement and are particularly useful for patients with loss of periodontal support. Current orthodontic opinion recommends either the use of 0.0215 inch multistrand wire, or 0.030 - 0.032 inch sandblasted round stainless steel wire.