Device for treating breathing problems, comprising - a lower part mountable on the lower jaw and an upper part mountable on the upper jaw, which lower and upper parts are adapted to be situated at least in the vicinity of the back teeth; and - left and right coupling means for coupling the lower part to the upper part close to the back teeth; wherein each of the left and right coupling means comprises an upper coupling element connected to the upper part and a lower coupling element connected to the lower part; which left and right coupling means are adapted to move the lower jaw forward in relation to the upper jaw; wherein the upper coupling element is provided with a stop for co-action with a contact surface of the lower coupling element; and wherein each upper coupling element (5, 6) is provided with a portion with a concave or convex surface directed toward the front teeth, and that each lower coupling element is provided with a complementarily shaped surface, this such that the upper coupling element can engage in the lower coupling element and that rearward movement of the lower jaw is avoided; characterized in that the upper and lower coupling elements (5, 6) are connected to respectively the upper and lower part such that these upper and lower coupling elements are situated in the oral vestibule in the position of the device placed in the mouth, and in that said stop and said contact surface are located in the oral vestibule, on the vestibular side of the tooth arch, in the position of the device placed in the mouth, such that when lower jaw and upper jaw are moved toward each other a further closing of the mouth is prevented when the contact surface comes up against the stop. - a lower part mountable on the lower jaw and an upper part mountable on the upper jaw, which lower and upper parts are adapted to be situated at least in the vicinity of the back teeth; and - left and right coupling means for coupling the lower part to the upper part close to the back teeth; wherein each of the left and right coupling means comprises an upper coupling element connected to the upper part and a lower coupling element connected to the lower part; which left and right coupling means are adapted to move the lower jaw forward in relation to the upper jaw; wherein the upper coupling element is provided with a stop for co-action with a contact surface of the lower coupling element; and wherein each upper coupling element (5, 6) is provided with a portion with a concave or convex surface directed toward the front teeth, and that each lower coupling element is provided with a complementarily shaped surface, this such that the upper coupling element can engage in the lower coupling element and that rearward movement of the lower jaw is avoided; characterized in that the upper and lower coupling elements (5, 6) are connected to respectively the upper and lower part such that these upper and lower coupling elements are situated in the oral vestibule in the position of the device placed in the mouth, and in that said stop and said contact surface are located in the oral vestibule, on the vestibular side of the tooth arch, in the position of the device placed in the mouth, such that when lower jaw and upper jaw are moved toward each other a further closing of the mouth is prevented when the contact surface comes up against the stop.