Key points
• As the aesthetic impact of orthognathic surgery is increasingly appreciated, occlusal plane rotation may be used by the surgeon to optimize facial balance. This approach requires bimaxillary surgery.
• Over impaction can cause a significantly “aged” appearance. Moreover, it is important to recall that the upper lip lengthens with age.
• It is generally felt that there is increased reliability when the maxillary surgery is performed first, followed by mandibular surgery and, finally, genioplasty.
• An advantage of maxillary first surgery is that the maxillary position will be dictated by the surgical splint not the mandible, which may not match the desired incisor angulation.
• Mandibular first surgery may be beneficial when a counterclockwise movement is desired in a patient with class II malocclusion to correct a steep occlusal plane. The intermediate splint places the dentition in close approximation, and the patient can be easily placed in maxillary–mandibular fixation.
• Custom surgical fixation eliminates the need for a surgical splint potentially increasing accuracy and reducing intraoperative time for the patient.
Introduction
The three fundamental procedures of orthognathic surgery—maxillary LeFort I osteotomy and its variations, mandibular bilateral sagittal split osteotomy, and osseous genioplasty—give the surgeon an incredible ability to safely disassemble the facial skeleton and reposition it to achieve the desired occlusion and facial appearance. Although functional occlusion can be achieved with either maxillary surgery alone or mandibular surgery alone, it is the ability to operate on both the maxilla and the mandible that gives the surgeon the greatest latitude to optimize the aesthetic facial form. The aesthetic appearance may be compromised with single-jaw surgery, even though the occlusal goals may be met. However, the ability to operate on both jaws simultaneously and reliably came much later.
Obwegeser described the bilateral sagittal split osteotomy (BSSO) in 1955, and mandibular surgery was used to solve a variety of dentofacial skeletal deformities even when the primary deformity was in the maxilla. A decade later, in 1965, Obwegeser described repositioning of the maxilla in a stable and consistent manner. Thus for the next decade or more, maxillary skeletal deformities were corrected by repositioning the maxilla via the LeFort I procedure to the mandible, and mandibular deformities were corrected by repositioning the mandible via the BSSO procedure to the maxilla. However, when both maxillary and mandibular deformities were identified, surgeons staged the procedures because of the complexity of presurgical planning, the technical difficulties in executing the procedures, and the time required to complete each of the procedures. While Obwegeser initially described the simultaneous two-jaw procedure in 1970, it took many years before it would become a routine procedure as it is today. One must remember that in those early years, the lack of instrumentation, the availability of only a drill to perforate the bone and an osteotome to sequentially complete the osteotomy, and the instability of wire osteosynthesis hampered the surgeon’s confidence in sectioning both jaws simultaneously. With time, the understanding of the need to appropriately align and level the dental arches before surgery to ensure postoperative stability and the development of plate/screw fixation were perhaps the two most important factors that increased the confidence of the surgeon that maxillary and mandibular deformities can be corrected in a single operation. As the maxillary and mandibular procedures are described in individual chapters, the focus of this chapter will be the indications for two-jaw surgery, planning, and operative sequencing.
Indications for two-jaw surgery
The decision to consider two-jaw surgery is based on the orthodontist’s and the surgeon’s ability to identify the problem in both the maxilla and the mandible, a problem that can only be corrected by repositioning both jaws. The single-jaw surgery should always be considered if it can achieve the desired goals without significant compromise. When it cannot, then the only option is two-jaw surgery. Both options and their advantages and limitations should be discussed; some patients will accept compromises in their preference for a single-jaw procedure.
The most obvious need is when there are skeletal and dental asymmetries that would necessitate two-jaw surgery. Each of the maxillary and mandibular dental arches may have roll, yaw, and pitch independent of each other ( Fig. 22.1 ). The maxillary and mandibular dental midlines may or may not be coincident with each other or with the facial skeletal midline. Moreover, even when the maxillary and mandibular dental arches are coordinated and the dental midlines match, the skeletal asymmetry in roll and yaw would require two-jaw surgery. In cases of unilateral condylar hyperplasia and mandibular hyperplasia/elongation, simultaneous maxillary advancement is beneficial to decrease the impact of the yaw correction on the condyles that occurs with the collision between the proximal and distal segments ( Fig. 22.2 A-C).
Two-jaw surgery is necessitated when occlusal plane changes are desired to optimize the aesthetic outcome. A classic example is a patient with class II malocclusion with a steep mandibular plane, who would benefit from a significant counterclockwise rotation. When the maxillary and mandibular occlusal planes are divergent, as in patients with apertognathia, posterior maxillary impaction may be insufficient, and mandibular surgery may be required for occlusal stability and aesthetic improvement ( Fig. 22.3 A-C).
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