When you come to the end of your orthodontic treatment your appliances will be removed and in most cases retainers will be fitted. 

The purpose of retainers is to minimize the movement of your teeth following orthodontic treatment because your teeth will want to move back towards their original positions. 

It is also important to realise that teeth continue to move throughout life and often crowding increases with age. 

If you want to try to prevent these normal age changes you can choose to keep wearing retainers on a long term basis but they will not last indefinitely and will require maintenance and replacement.