After completion of orthodontic treatment, the teeth tend to slip back towards their original positions. This, if allowed to happen, is known as 'relapse'. If teeth are likely to relapse, they are referred to as 'unstable' and the part of treatment that prevents this is called 'retention'. Many orthodontists regard retention and the longterm management of stability as one of the most important and difficult parts of orthodontic care.

What are retainers?
Retainers are simple appliances designed to hold the teeth in their new positions. In some ways, they are the opposite of braces as they prevent movement rather than cause it. The main types are:

• Removable Retainers. These are usually fitted to hold the upper teeth and consist of thin plastic in the roof of the mouth and a wire across the front teeth. They are usually worn day and night for three months (except for cleaning, eating and some sports) and subsequently just at night. It is eventually possible to reduce wear to just 2 or 3 nights a week.
• Vacuum Retainers. They are removable and made of a very thin sheet of clear plastic moulded to fit over either the upper or lower teeth.
• Fixed Retainers. These consist of fine wires bonded to the inner surfaces of the upper or lower front teeth. They are invisible and only require inspection every year or two. They are used particularly for the lower teeth as these are more prone to relapse.

Duration of Retention
Sometimes retention is only necessary for a few months but for most young patients, upper removable night time retention lasts 18 months and lower fixed retention lasts until the early 20s. For some patients, particularly adults, it is necessary to recommend prolonged or even lifelong retention to ensure continued enjoyment of the new smile.

Some problems are more prone to relapse than others. These can be divided into three groups:

• Problems with the teeth - These include gaps between the teeth, and twisted or overlapping front teeth.
• Problems with the treatment - Certain types of treatment are more likely to leave the teeth unstable. These include arch widening and pushing the lower incisors forward in many cases.
• Problems with the patient - Treatment after poor compliance with wearing the appliances provided and partial correction (as opposed to complete correction) are more likely to relapse.

Teeth move even without orthodontics
The teeth become more crowded and overlapping during the late teens and early twenties in people who have had no orthodontic treatment. This is so common it has to be regarded as normal. The reasons are complex but it is likely that the wisdom teeth are not the cause even though they are frequently blamed for this event. In fact, the teeth tend to become more crowded throughout life.