An expander is frequently used in orthodontic treatment to widen the upper jaw to make room for the teeth and to match better with the lower jaw.

The most common type of expander is the Hyrax, which is also referred to as a rapid palatal expander or a rapid maxillary expander. This is a metal appliance that is attached to the upper first molars and has a screw assembly in the middle that is turned or “activated” every day to widen the upper jaw in approximately a month.

The suture at the centre of the upper jaw widens quite easily up with this expansive pressure and allows the jaw to widen very predictably up to the age of approximately 15 years. The expander remains in place for 2 to 6 months following the active expansion as the bone in the palate regrows in the area that the suture has widened with the expansion.

There are also removable expanders that work on the same principle with an activation screw in the middle of the appliance. These removable appliances usually expand the upper jaw at a slower pace than the Hyrax expander.