8.1 Incision and Dissection

Although some technical modifications were made since H.L. Obwegeser introduced the combined maxilla and mandibular osteotomy techniques for orthognathic surgery in 1960s, the fundamental concepts of H.L. Obwegeser did not seem like changed [1]. The sequence of the orthognathic surgery varies according to the preference of the surgeons. Personally, I prefer the maxilla-first approach for patients with Class III deformities and facial asymmetry while I mostly do the mandible-first approach in patients with Class II deformities. I am sure that the orthognathic surgical procedures chould be completed effectively without complications if the surgeon was aware of the surgical anatomy and basic concept of this technique.

Regarding the issue whether the mandible first or maxilla first would be better, I decide this based on the vector of the maxilla. If I plan to perform the maxillary impaction on ANS or PNS, I prefer the maxillary first approach because the location of the condyle will not be changed after the fixation of the maxilla. On the contrary, in the case where the maxillary lengthening on ANS or PNS, I prefer the mandibular first approach because the condyle sag will be followed after the fixation of the maxilla. However, I always incise and dissect the mandible, first, and then start the maxilla. I start with the mandible to minimize bleeding and maintain the operative field relatively blood free. After the mandibular dissection, I pack the area with gauze and start dissection of the maxilla. During the dissection of the maxilla, bone bleeding can be controlled. After finishing the dissections of the mandible and maxilla, I start the mandibular osteotomy before completing the separation of the mandible. Then, I start a LeFort I osteotomy, followed by a sagittal split of the mandible. I believe my sequence is helpful for minimizing any bone bleeding that may occur during orthognathic surgery. However, the specific sequence may vary according to the situation, such as for patients with Class II dentofacial deformities where I initially perform mandible-first orthognathic surgery [2] (Fig. 8.1).

Subperiosteal inflation, with local anesthetics, is usually performed before draping. After nasotracheal intubation, a cutaneous injection of local anesthetic and epinephrine is administered in the subperiosteal plane of the ramus of the bilateral mandible. This local injection is very helpful as a part of the blood-free, subperiosteal dissection of the mandible.

A traditional buccogingival incision is made, using the cutting mode of a Bovie coagulator, down to the periosteum; a number 15 blade can also be used to achieve the same result. The lateral subperiosteal dissection is made using a round curved elevator, which facilitates the elevation of the periosteum and pterygomasseteric sling in a single plane; without dissection of the pterygomasseteric sling, a single-plane periosteal dissection is not possible. Then, I start elevation of the periosteum of the posterior and inferior borders of the mandible with 45° and 90° angled elevators; a U-shaped elevator is used to finalize the periosteal elevation.

For the medial dissection, determining the exact subperiosteal plane is crucial. I start to incise the bony periosteum using a Bovie coagulator or a number 15 blade, ensuring dissection of the subperiosteal plane. Using a curved elevator, I start the dissection of the medial parts of the mandible to locate the position of the horizontal osteotomy. Generally, the horizontal osteotomy line should be located between the sigmoid and lingual notches. A deep dissection should be made, to the posterior ramus (Fig. 8.1).