Some asymmetry phenomena can be corrected or improved by surgery, such as different height of bilateral cheekbones, different sizes of left and right mandibles, different sizes of mandibular angles, different sizes of mandibular margins and different sizes of left and right chins. Some of them are difficult or impossible to be corrected by surgery because of the limitations of basic conditions, such as the size of the left and right cheekbones, the size of the left and right zygomatic arches, and the degree of opening of the left and right dental arches.