Operations are performed under general anesthesia through orotracheal intubation. Local anesthesia solution containing 1% lidocaine and 1:100,000 epinephrine is infiltrated along the proposed incision line and dissection area, submucosally and also subperiosteally. A labial incision midway between the labial sulcus and the lower lip vermilion is made from the canine to the opposite canine, avoiding division of the frenulum. Subperiosteal dissection is then performed to expose the mid-symphyseal region. The dissection should not be done to totally deglove the inferior border of the mandible which may disturb blood supply to the bone segment. Great care should be taken to identify the mental nerves and to protect them during dissection. Dissection should be performed sufficiently posterior for adequate visualization and access for the osteotomy [1].

After dissection is completed, the symphyseal midline should be marked above and below the planned osteotomy. The osteotomy line should be designed at least 5 mm below the mental foramen, and the horizontality of the line should be double-checked. Then the osteotomy is completed with a reciprocating saw. As the distal bone segment gains mobility to allow manipulation, the segment should be advanced or set backed as planned according to preoperative profile analysis and rigidly fixed with plates and screws (Fig. 8.4) [7].

Meanwhile, a reduction or lengthening genioplasty can be performed to correct the chin deformity either with vertical excess or shortness. Usually when chin shortening is needed by a vertical reduction procedure, a horizontally parallel bone segment is removed from the chin (Fig. 8.5). After a reduction genioplasty, an additional marginal osteotomy or shaving is required as a step deformity can be noticed on each side of the chin. The steps may be approached through the same genioplasty incision with or without an extension, but an additional incision may be needed in cases with large steps. When the patient has a short lower face, a lengthening genioplasty may be planned to achieve ideal facial proportions [8]. The osteotomy for the lengthening genioplasty procedure contains a horizontal osteotomy with two vertical osteotomies in an upside-down trapezoidal shape [8]. While designing the line for the horizontal osteotomy, it is important to leave a small amount of the bone in the middle portion. The vertical height of the bony portion left in the center is in accordance with the amount that the chin is to be lengthened vertically (Fig. 8.6).

For correcting deformity of transverse excess and to make a slim lower face, a narrowing genioplasty is indicated [9, 10]. Horizontal osteotomy and two vertical osteotomies are designed as the amount of resection in the middle bony segment should be determined preoperatively. In cases with asymmetry, the center of the middle segment should be lateralized to the more prominent side. After the osteotomy is completed, the middle segment is removed, and the two lateral segments are fixed in the center (Fig. 8.7). To obtain a more natural-looking and smooth curvature in the lower border of the mandible, further osteotomy or shaving on the lateral steps is usually required [10]. Resection of bony steps can be extended to the mandible angle when performed as a combination with the mandible contouring procedure [11].