Two methods of dorsal preservation. (A, B, C) Push down operation (PDO) with a high septal resection followed by lateral and transverse osteotomies. Subsequent impaction of the bony vault downward into the pyriform aperture. (D, E, F) Let let down operation (LDO) with a high septal resection followed by resection of a portion of the ascending frontal process of the maxilla. Subsequent downward positioning of the bony vault onto the frontal process of the maxilla.