## 2 Materials and Methods
### Facial and Iliac Bone Generation and Visualization  
The VR simulator generates a model for maxillofacial reconstruction surgery using the iliac bone, requiring both iliac and facial bone models. The models are created based on CT volume images using Slicer 5.6.2 and 3 Ds Max 2024.2. Slicer 5.6.2 is software for processing CT volume images, while 3 Ds Max 2024.2 is used for post-processing the models. The generation process begins with reading facial and iliac bone CT images in DICOM format and converting them into volumetric data. DICOM images consist of numerous cross-sectional images, which are sequentially processed using Slicer 5.6.2. This software connects each cross-section continuously in 3D space to form three-dimensional volumetric data. Volumetric data are composed of voxels, rather than pixels, representing 3D-rendered information about the internal structures of the body. Secondly, the segmentation process is used to extract regions of interest (facial and pelvic areas) from volumetric data using automated segmentation algorithms (e.g., recommended threshold-based segmentation and clustering). If the extraction results are inaccurate, manual adjustment techniques, such as modifying threshold values or setting seed points for region-growing algorithms, are applied to improve accuracy. Thirdly, masking is performed to remove unnecessary parts,  
Figure 1: Schematic diagram of the development of a simulator for maxillofacial reconstruction. such as skin, muscles, and blood vessels, from the facial and pelvic areas, leaving only the facial and iliac bone structures. Fourthly, volume rendering is performed to visualize the masked bone structures in 3D. This process involves reconstructing specific regions in three dimensions based on the volumetric data and visually inspecting them. Volume rendering is an important step that helps verify whether the extracted data are accurately represented. Fifthly, the process of mesh generation and editing is applied to the 3D-visualized model. Mesh refers to the collection of polygons that form the surface of a 3D model, defining its structure and shape. Mesh generation involves converting the extracted bone structures into a polygonal mesh surface, making it usable in Computer-Aided Design (CAD) software or virtual environments. During this process, textures, materials, lighting, and shading can be added or modified to enhance the visual and physical properties of the model. Mesh editing involves removing unnecessary elements or smoothing the model to create a more natural form. Sixthly, the facial and iliac bone models are finalized through the processes of mesh reconstruction and retopology. Mesh reconstruction involves refining the existing mesh to add detailed features, while retopology focuses on removing unnecessary meshes, simplifying the structure, and reorganizing it. These processes create an optimized 3D model that can be efficiently utilized in CAD software or virtual environments. Figure 2 shows the process of generating a facial bone model. Exploration, manipulation, and resection tasks on the iliac and facial bone in a virtual environment require a visualization process. For this, the models are saved in formats such as DXF, OBJ, and FBX, which include the geometric structure, colors, and material  
Figure 2: Process for generating the facial bone 3D model: (**a**) Step 1, DICOM file loading; (**b**) Step 2, 3D model generation and select segmentation; (**c**) Step 3, masking; (**d**) Step 4, volume rendering; (**e**) Step 5, mesh removal; (**f**) Step 6, mesh detachment; (**g**) Step 7, mesh reconstruction; (**h**) Step 8, mesh retopology; and (**i**) Step 9, texture mapping. information of 3D models. These formats are compatible with virtual environment creation software like Unity (San Francisco, CA, USA). In the virtual environment, users can use the controller buttons to open a file browser, select the desired iliac bone or facial bone model, and visualize it in the virtual space.