A mandibular advancement device having an upper retainer positionable in front of teeth of a user's upper jaw and connected to a lower retainer positionable behind teeth of a user's lower jaw. The lower retainer comprises a support structure towards the rear of the lower retainer. The support structure has a shape and/or is made from a material such that, in use, a relatively high force is applied to two or more rearward teeth of the lower jaw to move the lower jaw forwards, and a relief region towards the front of the lower retainer configured to, in use, apply a relatively low force on one or more forward teeth of the lower jaw.
