A mandibular advancement device comprising: a first member, the first member configured to fit substantially over a portion of the teeth of the upper jaw of a user, and a second member, the second member configured to fit substantially over a portion of the teeth of the lower jaw of the user, and an engagement arrangement comprising a first member engagement means on the first member and a second member engagement means on the second member, wherein the first member engagement means and second member engagement means are configured to be engageable with one another upon a forward manipulation of the lower jaw by the user, to maintain the lower jaw of the user in a predetermined protruding position relative to the upper jaw of the user and the natural biting position of the lower jaw, and wherein the engagement arrangement further comprises articulation restriction means comprising a first member restrictive element on the first member and a second member restrictive element on the second member, the first member restrictive element and second member restrictive element are configured to be engageable with one another to restrict articulation of the lower jaw of the user when the first member engagement means and second member engagement means are engaged and the lower jaw of the user is in the predetermined protruding position, and characterised in that the engagement arrangement further comprises a braking means to halt the forward sliding movement of the lower jaw of the user, the braking means is a protrusion protruding from a portion of the second member, and guide means to guide the first member engagement means to the second member engagement means for the securement of the second member in the protruding position, wherein the guide means extends between the second member restrictive element and the braking means. a first member, the first member configured to fit substantially over a portion of the teeth of the upper jaw of a user, and a second member, the second member configured to fit substantially over a portion of the teeth of the lower jaw of the user, and an engagement arrangement comprising a first member engagement means on the first member and a second member engagement means on the second member, wherein the first member engagement means and second member engagement means are configured to be engageable with one another upon a forward manipulation of the lower jaw by the user, to maintain the lower jaw of the user in a predetermined protruding position relative to the upper jaw of the user and the natural biting position of the lower jaw, and wherein the engagement arrangement further comprises articulation restriction means comprising a first member restrictive element on the first member and a second member restrictive element on the second member, the first member restrictive element and second member restrictive element are configured to be engageable with one another to restrict articulation of the lower jaw of the user when the first member engagement means and second member engagement means are engaged and the lower jaw of the user is in the predetermined protruding position, and characterised in that the engagement arrangement further comprises a braking means to halt the forward sliding movement of the lower jaw of the user, the braking means is a protrusion protruding from a portion of the second member, and guide means to guide the first member engagement means to the second member engagement means for the securement of the second member in the protruding position, wherein the guide means extends between the second member restrictive element and the braking means.