Abstract: A lenticular, rigid, optionally hollow, molded plastic part wet-resistant toward aqueous media, for example acryl glass, is proposed as an implantable temporary filler for a mammary gland prosthesis that can be implanted in surgery following amputation of the mammary gland until after the healing of the site of the operation. The molded part has an oval horizontal projection and is bounded by two curved surfaces, one of them a concave and an approximately cylindrical surface whose curvature is adapted to the human thorax in the area of the breast and the other an approximately spherical surface whose radius is smaller than the radius of curvature of the cylindrical surface.