Apparatus for the alleviation of sleep apnoea in which dentition engagement units or dental overlays shaped to engage the maxillary and mandibular dentition of a subject each having a laterally located pair of flanges the ends of which almost abut, magnets embedded in said flanges with their like poles adjacent or sinusoidally-shaped extension elements made from shape-memory material having a transition temperature equal to or slightly less than normal body temperature and accommodated in cavities in said flanges provide, respectively, a magnetic repulsion force or expansive force when warmed by body heat sufficient, during sleep-induced relaxation, to displace said mandibular dentition engagement unit or dental overlay forwardly in relation to said maxillary dentition engagement unit, displacing the mandible of the subject and thereby effecting a displacement of the temporomandibular joint.