Headgear is any orthodontic device that is worn on the outside of the mouth in order to move the top molar teeth backwards, in turn creating more space in the jaw and eliminating the need for teeth to be extracted.
Headgear can also be used to help correct an overbite (or 'overjet') or an underbite. Where it is used to correct an underbite it is called 'reverse pull' headgear.
As headgear is primarily used to influence growth of the upper jaw, it is used mostly with children whose jaws have not fully set, i.e. before the age of eleven.
Headgear is normally only worn either at home or while the wearer is asleep.