A device for the mandibular advancement, a process for making an appliance for the mandibular advancement and the appliance realized. The device includes a first engagement element associable with the lower dental arch or mandible and a second engagement element associable with the upper dental arch or maxilla. The engagement elements are provided with a first inclined engagement surface and a second inclined engagement surface for determining said mandibular advancement. The first engagement element includes a core covered by a covering body provided with a pocket adapted to the housing of the core, the second engagement element includes an orthodontic screw adapted to determine the displacement of the second inclined plane, the core having an inclined portion destined to define, in cooperation with the respective covering, the first inclined engagement surface.