Surgical Approach for Class III Skeletal Deformity
Lun-Jou Lo, MD
Craniofacial Center, Department of Plastic & Reconstructive Surgery
Chang Gung Memorial Hospital, Linkou
Orthognathic surgery (OGS) aims to correct dental malocclusion as well as facial aesthetic problem. In class III deformity, preoperative evaluation focuses on maxillary as well as mandibular position and relationship to set up a surgical plan. Our current OGS practice has been using two-jaw surgery and a single occlusal splint for most of the patients with class III skeletal deformity.
Surgery is started to perform mandibular ramus osteotomy first. Bilateral sagittal split osteotomy (BSSO) is preferred as osseous fixation is more convenient without postoperative use of intermaxillary immobilization. A modified method of Hunsuck or Dal Pont-Obwegeser is used for BSSO. Injury to the inferior alveolar nerve is reduced. LeFort I osteotomy is performed following the BSSO. The mandibular and maxillary segments are released, brought together and fixed into the final occlusal splint, forming the maxillomandibular complex (MMC). The MMC is then mobilized to the final planned position according to the surgical plan. Several methods could be used for accurate position of the MMC, including 3D simulation images, positioning guides, and navigation. Fixation of the MMC begins with the LeFort I level using plates and screws. At this step, the position of MMC is again checked for its midline, level, symmetry, and pitch. Then fixation of the ramus segments is performed using plates and screws or transcutaneous bicortical screws. The intermaxillary fixation is released, and the occlusion is checked. Genioplasty is performed as indicated. The shape and size of chin is important for final facial aesthetics. At this moment, the whole face is carefully evaluated and contouring can be performed for correction of facial asymmetry.