Effect of Proximal Segment Positioning on Postoperative Condylar Remodeling in Bimaxillary Orthognathic Surgery

The Effect Of Different Proximal Segment Positioning Methods On Postoperative Condylar Remodeling in Patients Undergoing Bimaxillary Orthognathic Surgery

Bimaxillary orthognathic surgery is a surgical procedure that involves simultaneous corrections to both the maxilla (upper jaw) and mandible (lower jaw). This surgery is performed to correct facial and jaw deformities, improve occlusion, and enhance facial symmetry. The need for orthognathic surgery typically arises in cases where there is a significant discrepancy between the upper and lower jaws or severe malocclusion.

In bimaxillary orthognathic surgery, following mandibular osteotomies, the lower jaw is divided into two segments: the distal segment, which contains the teeth, and the proximal segment, which includes the condylar head. While the distal segment is positioned according to the ideal occlusion planned in collaboration with orthodontists using digital design, the management of the proximal segment varies among surgeons. Some surgeons leave the proximal segment in its original position without mobilization, whereas others reposition it through rotational movements.

This study aims to evaluate condylar remodeling by comparing these two surgical approaches in patients divided into two groups, assessing how each technique affects postoperative outcomes.

Bimaxillary orthognathic surgery is a surgical procedure that involves simultaneous correction of both the maxilla (upper jaw) and the mandible (lower jaw). This surgery is performed to correct facial and jaw deformities, improve occlusion, and enhance facial symmetry. The need for orthognathic surgery typically arises in cases where there is a discrepancy between the upper and lower jaws or significant malocclusion.

In bimaxillary orthognathic surgery, following mandibular osteotomies, the lower jaw is divided into two segments: the distal segment, which contains the teeth, and the proximal segment, which includes the condylar head. While the distal segment is positioned according to the ideal occlusion planned in collaboration with orthodontists using digital design, the management of the proximal segment varies among surgeons. Some surgeons leave the proximal segment in its original position without mobilization, whereas others reposition it through rotational movements.

This study aims to evaluate condylar remodeling by applying both surgical approaches to patients divided into two groups. The study will assess how each surgical technique affects condylar remodeling both in terms of angular and volumetric changes, determining which approach better preserves and reshapes the joint optimally. Ultimately, the findings will contribute to the future course of bimaxillary orthognathic surgeries and their benefits for patients.

Since 1990, cone-beam computed tomography (CBCT) has been effectively used in oral and maxillofacial surgery as an alternative to conventional computed tomography (CT). Compared to CT, CBCT has demonstrated advantages such as requiring a lower radiation dose, producing fewer metal artifacts, being more accessible, and offering easier usage. Due to these advantages, CBCT has been successfully utilized in oral implant applications, where a localized focus area is necessary. However, limitations such as low contrast range, restricted detector size, limited soft tissue information, increased noise due to scattered radiation, and a subsequent loss of contrast resolution, along with its inability to determine Hounsfield units (HU), restrict its use in maxillofacial applications.

Particularly in preoperative digital planning for orthognathic surgery and subsequent evaluations, it is crucial to select an appropriate HU range to segment the maxilla and mandible and accurately transfer all topographic features into the digital domain. This step forms the foundation of patient-specific virtual surgical planning, which requires the use of computed tomography (CT) for optimal execution. Studies have preferred CT as the imaging method due to its high accuracy in topographic transfer and its ability to provide precise cortical bone thickness, a critical factor for designing patient-specific guides and plates. For these reasons, we also plan to use CT imaging in our study.

Inclusion Criteria:

1. Patients planned to undergo bimaxillary orthognathic surgery with Class III skeletal deformity
2. Patients aged 18-65
3. Patients who have undergone preoperative orthodontic treatment
4. Patients who, after mandibular distal segment sagittal split osteotomy, exhibit a maximum of 4 degrees of counterclockwise rotation when brought to the final position

Exclusion Criteria:

1. Patients with a history of joint surgery, orthognathic surgery, or tumor resection
2. Patients with facial asymmetry
3. Patients with cleft lip and palate syndrome, craniofacial syndrome, or trauma
4. Patients who, after mandibular distal segment sagittal split osteotomy, exhibit more than 4 degrees of counterclockwise rotation when brought to the final position (as the amount of base resection required in this case would exceed feasible limits).