## 2 Materials and Methods  
Following informed consent, computed tomography (CT) scan data was obtained from a 45-year-old male patient who was previously treated by surgical resection for left mandibular tumor involving the TMJ. The CT data acquired as two-dimensional (2D) DICOM (Digital Image and Communications in Medicine) file format were processed into digital three-dimensional (3D) models using Materialise-MIMICS 17.0(r) (Materialise Interactive Medical Image Control System; (c)2014 Materialise NV, Leuven, Belgium) software (Figure 1). In the next step, the digital 3D model was subjected to pixel- based image segmentation and region growing technique using MIMICS(r) to achieve the region of interest, which was the entire skull in the present case (Figure 2). The skull model obtained through the region growing technique was exported to Standard Tessellation Language (STL) file format for custom processing and design of prosthetic TMJ condyle and glenoid fossa.  
The custom design process utilized a mirror reconstruction technique based on healthy bone in the unaffected side, using 3-Matic 9.0(r) software ((c)2014 Materialise NV, Leuven, Belgium) [16; 19]. The steps involved in mirror reconstruction and designing the custom TMJ parts (condyle and glenoid fossa)  
Figure 1: Two-dimensional computed tomography data acquired from the patient (**a**) coronal section; (**b**) axial section; (**c**) sagittal section, converted into digital three-dimensional models, (**d**) volume rendering with inset image showing the complete destruction of temporomandibular joint (TMJ) anatomy on the left side.  
Figure 2: Three-dimensional model of the region of interest (skull) generated using image segmentation and region growing technique in Materialise Interactive Medical Image Control System (MIMICS®).  
are outlined in Figure 3. In order to biomechanically test the prosthetic TMJ parts under functional simulation of jaw movements, the condyle and fossa regions from the custom fabricated digital 3D models were separated (Figure 4). The separated TMJ condyle and fossa parts were imported into Magics(r) 18.03 software (c)2014 Materialise, NV, Belgium) for STL fixing, support generation and build orientation, and the in-built automatic diagnostic tool was used for fixing STL errors. These error free STL files were finally utilized for custom fabrication of the TMJ parts using different biomaterials, namely EBM titanium alloy (EBM-Ti), zirconia, and poly (methyl methacrylate) (acrylic).  
Figure 3: Mirror reconstruction technique and steps in custom designing the prosthetic left TMJ condyle and glenoid fossa parts using 3-Matics 9.0® software; (**a**) three-dimensional (3D) skull model generated using Standard Tessellation Language (STL) files, (**b**) superior and inferior end points of the model marked to assign a central plane dividing the skull into symmetrical halves, (**c**) right side skull with the left half digitally subtracted, (**d**) mirroring of the right half skull on the left side, (**e**) and (**f**) clean skull model obtained after Boolean subtraction operation between the skull model with tumor and mirror reconstructed skull model (**g**) reconstructed model of the left hemi-mandible along with condyle, (**h**) custom design of the prosthetic TMJ condyle along with plate extension for fixation to the ramus of the mandible, (**i**) reconstructed model of the left glenoid fossa (blue), (**j**) custom design of the prosthetic TMJ glenoid fossa along with plate extension for fixation to the temporal bone.