Maintaining the treatment result following the orthodontic movement is the most difficult task of the entire treatment process. It is the biggest challenge a dentist has to face after the treatment is over. It has been proved that the teeth moved through the bone using an orthodontic appliance have a tendency to return back to their original position.
Hence, Retention may be defined as “maintaining the newly moved teeth in ideal functional and esthetic position.” Normal maturational changes, together with post treatment tooth alterations make it difficult for long term stability. When a dentist remove a patient braces, that patient from that moment enters into the ‘Retention stage of the treatment’ which is more important than active or braces stage of the treatment.
Relapse has been defined as “the loss of any correction achieved by orthodontic treatment”.
Stabilizing the treatment results by retention procedures is an integral part of orthodontic therapy. The method of retention to be employed is best selected at the start of treatment itself and should be employed in each treatment plan.
Causes of Relapse
Numerous factors are responsible for relapse. No single factor can be said to be the sole cause of relapse. In most cases, relapse occurs due to combination of causes-
1. Periodontal Ligament Factors
Whenever teeth are moved orthodontically through braces, the periodontal and gingival fibres that encircle the tooth are stretched. These stretched fibres can contract and can cause the teeth to come back to their original untreated position causing the relapse. These fibres need some time to reorganize themselves to this newly accomplished position. Hence after the comprehensive orthodontic treatment, teeth require 4-5 months of full time retention so as to allow the reorganization of these fibres.
2. Relapse Due to Growth Related Changes- Growth is a process that continues throughout life. Patients with skeletal problems may exhibit relapse due to continuation of the abnormal growth pattern after orthodontic therapy. Hence prolonged retention is indicated until active growth is completed.
3. Bone Adaptation- Bone is the basic support to the tooth. Teeth that have been moved recently are surrounded by lightly calcified bone. Thus the teeth are not adequately stabilized and have a tendency to move to their original position.
4. Periodontal Ligament Factors Muscular Forces- Soft tissues can influence the position of the teeth to a larger extent. Teeth are surrounded in all directions by a blanket of muscles. The tongue applies forces which will move the teeth buccally/labially and cheeks and lips oppose these forces. The teeth lie in the theoretical area of balance between these two sets of forces called the neutral zone. Hence it is highly beneficial that at the end of the treatment the teeth are positioned in the neutral zone.
5. Failure to Eliminate the Original Cause- The cause of the malocclusion should be determined at the time of diagnosis and adequate treatment steps should be planned to eliminate them. Failure to remove the etiology can result in relapse e.g. some times the orthodontic problem is because of some habit like thumb sucking or mouth breathing. If at the time of start of the treatment the cause that is the habit is not diagnosed and is not treated before then after the braces are removed the relapse will be there.
6. Role of Third Molars- The third molars erupt very late in the development of dentition. They erupt in most cases between the ages of 18-21 years. By this time most of the
patients have completed their orthodontic treatment. The pressure exerted by the erupting third molars is believed to cause the late anterior crowding causing relapse.
7. Role of Occlusion- Good intercuspation of upper and lower teeth is important factor in maintaining the stability of treated cases. Presence of certain habits such as clenching, grinding, nail biting, lip biting are important causes of relapse.
Why is Retention Needed?
Retention is Needed Because of Following Reasons
Corrected teeth tend to return to their original position.
Relapse is likely to occur if corrections are carried out during periods of growth.
Lower incisors are more likely to remain in good alignment if position upright over basal bone.
Overcorrection is recommended in malocclusion
Relapse is likely to occur if the cause of malocclusion is eliminated.
Obtaining proper occlusion is an important factor in maintaining corrected positions.
The farther the teeth have been moved, lesser is the risk of relapse.
Bone and adjacent tissues must be allowed time to reorganize around newly positioned teeth.
Arch form particularly in the mandibular arch cannot be permanently altered by appliance therapy.
Many treated malocclusions require permanent retaining devices.
Types of Retention
How to Achieve Retention?
1. Retention can be achieved by placing removable or fixed retainers. There is no recognized duration for retention, although it has been shown that at least in relation to periodontal factors, it takes on average a minimum of 232 days for fibres around the teeth to remodel to the new tooth position. However, even if the teeth are held in position during this period, they can show relapse. Hence some dentists therefore prefer to retain for longer periods, sometimes indefinitely.
Retainers- Retainers are passive orthodontic appliances that help in maintain and stabilizing the position of teeth long enough to permit reorganization of the supporting structures after active phase of orthodontic therapy.
Types of Retainers
Removable Retainers- These appliances can be removed by the patient and reinserted at his own will. The main drawback of removable retainer is that the patient may not wear the retainer leading to relapse again.
Fixed Retainers- These retainers are fixed or fitted on to teeth and cannot be removed and reinserted by the patient
How Long These Retainers Should Be Worn?
There is no fixed time duration on the length of time of the retention phase of the treatment. This duration should be decided specifically for each patient. Following points a dentist should keep in mind while determining the type of retentive measures and their duration
How many teeth have been moved and how far
Age of patient and future growth
Cause of particular malocclusion
Rapidness of correction
Health of tissues involved
Size of arches
In most of the cases, retainers are to be worn for 6 months initially and then are to be worn only at night for 6 months and gradually withdrawing them. Fixed bonded retainers are becoming popular these days.
Treatment with fixed orthodontic appliances in case of rotated teeth should follow at least 12 months of retention- 3-4 months full time and 8-9 months part time. The retention phase may then be ceased but in growing patients it should continue until growth declines.
To prevent relapse with late growth lower teeth alignment, indefinite retention is required.
Retention of periodontally weak teeth, space closure and arch alignment cases too require permanent retention.
2. Additional or adjunctive procedures can also be applied to the teeth or surrounding periodontium to aid the retention process. Examples include
Reshaping Teeth- such as interproximal stripping – in this small amount of tooth portion is removed to create space with the aim of increasing the stability between adjacent teeth.
Percision- is the process of cutting the gingival fibres which are responsible for pulling the teeth back to their original position.