A mandibular advancement device (26) includes a lower part (28), a lower flange (34), an upper part (30) and an upper flange (32). The lower part (28) is releasably attachable to at least a portion of a lower jaw (24). The lower flange (38) has a lower engagement surface extending upwardly from the lower part (28). The upper part (30) is releasably attachable to at least a portion of an upper jaw (22). The upper flange (32) has an upper engagement surface extending downwardly from the upper part (30). The lower flange (34) is connected to the lower part (28) by a lower one way ratchet means configured to only allow uni-directional posterior movement of the lower flange (34) relative to the lower part (28) and/or the upper flange (32) is connected to the upper part (30) by an upper one way ratchet means configured to only allow uni- directional anterior movement of the upper flange (32) relative to the upper part (30). When the lower part (28) and the upper part (30) are fitted to the jaws (22,24) of a patient for use in sleep, the lower engagement surface and the upper engagement surface engage in a manner to cause anterior advancement of the lower jaw (24) from the reflex path of opening.
