This study aims to evaluate the clinical efficacy and positioning accuracy of a custom-made proximal segment positioning appliance designed for use in sagittal split ramus osteotomy (SSRO). The appliance is produced using STL-based digital planning and 3D printing technologies. In each patient, the appliance is applied to one side of the mandible while the contralateral side is positioned using the conventional manual method. This within-subject design enables direct comparison by eliminating inter-individual anatomical variability. The primary outcome is the accuracy of segment positioning, evaluated by 3D superimposition and deviation analysis of pre- and postoperative STL models. Secondary outcomes include surgical time, ease of use as rated by the surgeon, and postoperative temporomandibular joint symptoms. The study will enroll 30 adult patients undergoing SSRO or double-jaw surgery due to dentofacial deformities. The results are expected to provide high-level clinical evidence for the reliability of patient-specific appliances in orthognathic surgery.

Sagittal split ramus osteotomy (SSRO) is a widely used orthognathic surgery technique to correct mandibular deformities. During SSRO, accurate positioning of the proximal segment is critical for ensuring temporomandibular joint (TMJ) health, symmetry, and long-term surgical stability. However, conventional positioning relies heavily on the surgeon's visual judgment and experience, which may lead to postoperative complications such as condylar displacement, facial asymmetry, and TMJ dysfunction.

This prospective, randomized clinical study introduces a patient-specific proximal segment positioning appliance developed through STL-based 3D design using Blender and printed with biocompatible surgical guide resin via a Formlabs SLA 3D printer. Each patient will undergo SSRO (with or without Le Fort I osteotomy), and the custom appliance will be used to guide the proximal segment on one mandibular side. The opposite side will be positioned conventionally, allowing intra-patient comparison.

Postoperative CBCT images will be obtained at 1 month and converted to STL format. These models will be aligned with preoperative plans using MeshLab software to evaluate linear and rotational deviations. Surgical time, ease of application, and TMJ symptoms will be documented. Statistical analysis will include paired t-tests or Wilcoxon signed-rank tests depending on data distribution.

This study will generate clinically meaningful data regarding the effectiveness and safety of patient-specific guides in mandibular segment positioning. The proposed method also holds commercialization potential and may reduce intraoperative variability and dependence on surgeon experience.

Inclusion Criteria:

• Patients scheduled to undergo bilateral sagittal split ramus osteotomy as part of orthognathic surgery
• Age ≥ 18 years
• Availability of preoperative and postoperative CT scans
• Consent to participate in the study

Exclusion Criteria:

• History of previous mandibular surgery
• Craniofacial syndromes or congenital deformities
• Incomplete radiological records

Individual participant data (IPD) will not be shared due to privacy concerns and institutional policy restrictions regarding the sharing of de-identified clinical data.