Analysis of Mandibular Proximal Segment Position Using Virtual Orthognathic Surgical Planning, Individualized Guides, and Osteosynthesis Plates

Orthognathic surgery is a frequently used treatment method for correcting dentofacial deformities. Bilateral sagittal split osteotomy (BSSO), developed by Trauner and Obwegeser, is still used today with many design modifications. There is a potential for incorrect positioning of the proximal segment during fixation. Regarding mandibular setback surgery, many authors have reported a tendency for medial and posterior rotation of the proximal segment during the postoperative period. Proximal segment displacement may result from the condyle not seating properly in the fossa or from early contacts between the proximal and distal segments. These early contacts cause rotation of the proximal segment while the mandible is fixed. If the displacement exceeds the adaptive capacity of the condyle, a high rate of condylar resorption or postoperative relapse may occur. Various condylar positioning devices have been developed to overcome this issue.

The introduction of virtual surgical planning (VSP) has helped to overcome some of the errors and difficulties in model surgery and conventional surgical planning. Computer-aided design and manufacturing (CAD/CAM) splints have been shown to be accurate in transferring the surgical plan to real life, but some errors may still occur. Patient-specific 3D-printed osteosynthesis plates have been developed to overcome these errors. Many studies have reported high accuracy of these plates in the maxilla. However, some other studies have reported errors of 5-6 mm. Similar accuracy rates have been reported for the mandible, but there are fewer studies in this area.

VSP not only allows the surgeon to visualize 3D movements but also shows the osteotomy design, screw placement locations, fixation design, and early bone contacts. The amount of trimming of the distal segment is determined by examining whether any openings or narrowings occur after minor movements are made to the proximal segment based on the rotation of the distal segment or the complex "pitch" and "roll" movements of the occlusal plane. After all these movements are given with virtual planning, personalized cutting guides, positioning guides, and patient-specific plates are needed to transfer this plan to real life.

Recent developments in VSP have focused on accurately transferring preoperative planning to surgery. The most significant development in this regard is patient-specific plates and cutting guides. This technology enables surgeons and engineers to produce patient-specific cutting guides to determine the incision lines. These guides also determine the thickness of the bone in the areas where plate screws will be placed and ensure avoidance of tooth roots. Patient-specific plates are designed and manufactured to fit into pre-prepared holes and hold the osteotomized segments together in the desired position. Despite being a new technology, several studies have shown that VSP and patient-specific plates have better final surgical accuracies compared to VSP and splints.

Inclusion criteria

• Healthy individuals over 18 years of age
• Patients with skeletal Class 2 and Class 3 malocclusion requiring bimaxillary orthognathic surgery
• Patients who have undergone orthodontic treatment prior to surgery

Exclusion criteria

• Patients with cleft lip and palate or craniofacial deformities
• Oligodontia
• Patients in whom the study protocol could not be continued due to intraoperative complications such as guide mismatch or bad split, or due to reasons such as inability to obtain postoperative CT scans
• Patients with pre-existing temporomandibular joint disorders prior to surgery
• Patients who have undergone previous orthognathic surgery
• Patients with a history of maxillary or mandibular trauma
• Patients requiring segmental maxillary surgery
• Patients with bone metabolism disorders
• Patients allergic to titanium
• Pregnant individuals