Stability of Two Designs of Patient Specific Osteosynthesis For Fixation of LeFort 1 Osteotomy in Orthognathic Surgery

A comparison of the stability of two different designs of patient specific fixation devices for the performance of splintless computer guided le fort 1 osteotomy in orthognathic surgery workflow for the correction of a variety of dentofacial deformities

• Intervention Group: - Pre-Operative Virtual planning: After CT examinations, further processing of the DICOM files (Digital Imaging and Communications in Medicine) will be performed using the specialized DICOM image processing software and reconstructed 3D models of the skull will be made. Stone models will be scanned using an optical scanner and stereolithographic files will be imported. Registration of the STL files with the skull model will create a composite model suitable for the construction of necessary devices. These 3D models will be used to design the custom-made cutting guides and fixation devices. The final STL files will be sent to the lab to be milled/printed. Surgical procedure: Routine site preparation regarding L.A injections and surgical site disinfections. A maxillary vestibular incision will be made from the maxillary second premolar on one side to the contralateral tooth. The incision will be made 5 mm above the mucogingival junction to leave an adequate cuff for closure. A full thickness mucoperiosteal flap will be reflected to expose the anterior and lateral maxillary walls. Superiorly the reflection exposes the pyriform rim, lateral nasal wall and the infraorbital nerve. Moving backwards, exposure of the zygomatico maxillary buttress is done followed by the maxillary tuberosity and finally the pterygomaxillary junction. The cutting guides will then be placed on the exposed maxilla. The cutting guides will have holes designed in them corresponding to the position of the fixation screws and a slot marking the level of the level of the Le fort 1 osteotomy which will be made using a reciprocating saw. The osteotomy is initiated and the cutting guide is removed. The nasal septum, both lateral nasal walls and both pterygomaxillary junctions will be osteotomized using a mallet and a chisel and the maxilla finally down fractured and mobilized using Rowe's disimpaction forceps. Without the use of inter maxillary fixation on an interocclusal wafer. the two-piece PSI will be placed and fixated above the level of the osteotomy using Mini screws. The mobile maxilla is moved until its one and only preplanned position is achieved using the PSI anatomical contours and then the maxilla is fixed. Copious irrigation is done and wound closure using an air cinch and a V-Y closure. Post-Operative: Immediate post-operative instructions and medications including analgesics and antibiotics will be given to the patient. CT scan will be done 4 months post operatively. Then the preoperative and postoperative models will be superimposed to determine the accuracy of the surgically positioned maxilla, comparing it to the virtual plan. • Control Group The surgical procedure: The exact same procedure will be repeated for the control group with the only difference being the fixation device which will consist of a one piece PSI spanning along the entire length of the osteotomy from one zygomaticomaxillary buttress to another. Post-Operative: Immediate post-operative instructions and medications including analgesics and antibiotics will be given to the patient. CT scan will be done 4 months postoperatively. Strategies to improve adherence to intervention protocols: Assuring the accuracy of the patient specific fixation by printing skull models of the performed surgery and checking the plates. And such accuracy measures will be photographed and archived. Criteria for discontinuing allocated interventions for a participant: * Significant deviation from the virtual plan which will compromise the treatment outcome. * Hardware failure (Non healing wound dehiscence, screw loosening, plate fracture, etc.) Relevant concomitant care and interventions that are permitted: \- The application of postoperative elastics for minor occlusal adjustments. Relevant concomitant care that will be prohibited is the fixation of the separated maxilla in a position other than that dictated by the cutting and drilling guide