The unstable condylar position in the glenoid fossa is a critical problem for postsurgical instability after mandibular advancement with subsequent mandibular relapse. The habitual forward occlusion in class II patients creates unstable condyle to glenoid fossa relationship making it hard for clinicians to determine the amount of mandibular advancement. Splint therapy is considered as a preoperative reversible nonsurgical condylar repositioning option in addition to its adjunctive effect for pain relief in TMJ symptomatic patients. To minimize this relapse, presurgical functional appliance therapy has been proposed and has shown promising outcomes.

The aim of this study is to compare the effect of postsurgical versus presurgical computer guided functional appliance in relapse prevention after mandibular advancement surgery.

Surgical procedure:

1. Owbgeser incision will be performed to expose the buccal and lingual aspects of the ramus angle region.
2. CAD/CAM generated preoperative wafer will be placed on the lower arch dentition, the guide has an extension to guide medial, vertical, oblique cuts as well as screw holes for reference landmarks for proximal segment & tooth bearing segment.
3. Drilling of all the reference landmarks on the proximal segment and locating medial, vertical, oblique cuts.
4. Removal of guide, then BSSO is performed.
5. The final wafer is placed, the guiding hole on the proximal segment will then be realigned with the previously drilled screw holes, fixation using mono cortical screws then drilling screw holes for plate fixation.
6. Fixation of the osteotomy using 2.0 mm pre-bent mini plates.
7. A positioning screw will be added to improve stability against rotational forces.

b-Functional appliance

Postsurgical computer guided functional appliance:

After achieving ideal condylar poison by computer guided surgery. The distal extension of the final occlusal wafer will be cut and the appliance will be fitted to be utilized as a postsurgical functional appliance for condylar adaptation. Patients will be instructed to wear the splints continuously for 3 months, only being allowed to remove them when eating and brushing their teeth.

Presurgical computer guided functional appliance:

Using the software, 3D digitized mandible will be virtually repositioned in ideal centric relation through accurate adjustment of the condyle in its glenoid fossa. Patients' dental casts will be scanned, and digitized into a virtual 3D model and superimposed to the CT cuts into the virtual plan software environment in order to produce preoperative CAD/CAM splint on the adjusted centric occlusion. Patients will be instructed to wear the splints continuously for 3 months, only being allowed to remove them when eating and brushing their teeth.

c- Follow up

All patients will be advised to stay on a soft diet for 4-6 weeks to avoid any undue forces on the surgical site. Postoperative CT and lateral cephalogram will be obtained, immediately postoperative and 12 months later respectively.

Inclusion Criteria:

• Age of the patient above 18 years
• Patients in need of bilateral sagittal split osteotomy for mandibular advancement.
• All patients are free from any systemic disease that may affect normal bone healing.
• Sufficient dentition to reproduce the occlusal relationships
• Patient's consent to participate

Exclusion Criteria:

• Patients with any systemic disease that may affect normal healing
• Intra-bony lesions or infections that may interfere with surgery
• Previous orthognathic surgeries

Single blinding