A device for advancing a lower jaw relative to an upper jaw in a mouth, the device comprising an upper member arranged to be positioned behind the upper front teeth in the upper jaw and configured to extend back towards the upper molars on either side of the upper jaw, the upper member having retaining means for retaining the upper member within the upper jaw by engagement with one or more of the upper molars a lower member, arranged to be positioned forward of the lower front teeth in the lower jaw and configured to extend backwards to cover at least part of the occlusal surfaces of one or more of the lower molars on either side of the lower jaw, the lower member having retaining means for retaining it within the lower jaw by engagement with one or more of the lower molars and connection means configured to removably connect the upper member to the lower member such that the lower jaw is advanced to and retained at a predetermined minimum distance relative to the upper jaw.
