A device 1 for insertion into the mouth of a user to relieve or prevent sleep apnoea and snoring includes wing portions 22, 23 projecting either side of a central portion 3. The wing portions include heat mouldable plastic so that the device once heated can be inserted into the mouth for the user to bite down onto the wing portions to form contours that will inter-engage with the teeth to hold the device firmly in a set position in the mouth. The bottom surface 4 of the central portion is provided with projections that will gently engage the top surface of the tongue to prevent the tongue from falling back to block the airway while the wearer is asleep, so that the wearer continues to be a breather. The central portion is in the shape of a rectangular channel which in use is located between and not fixed to the lower teeth.
