## 2 Materials and Methods
### Virtual Planning Workflow  
Brainlab CMF software (iPlan) (Brainlab, Germany) was used as the workstation for the planning pertaining to computer-aided design (CAD). DICOM (Digital Imaging Communications in Medicine) data of the CT/MRI of the primary lesion before ablative surgery was obtained from the institution's radiology database if available. The virtual planning workflow is illustrated in Figure 1. The advantage of the proposed algorithm is that it provides the readers with basic information on the virtual planning algorithm in addition to methods of achieving 3D template for printing the mandibular model in various defect scenarios. Category I included the cases where the reconstruction defect did not cross the midline. 'Mirroring' function integrated in the software was used to obtain the template of the defect from the normal sided mandible and whole mandible could be virtually constructed. Since the position of residual mandible is distorted in most of cases of secondary reconstructions, the residual mandible was also realigned to near-original position, taking occlusal relation as a guide and then mirroring it (Figure 2). In category II, the ablative defect extended past the midline. CT/MRI taken before the primary surgery were superimposed over the postoperative/current imaging, necessary realignment of the residual segment was carried out and then mirrored. The unresected portion from the previous imaging was then used as template to manually delineate the mandibular contour to reproduce a whole mandible (Figure 3). Category III included the cases where defect crossed the midline, but since primary surgery was carried out elsewhere, previous imaging data were not available. In those cases, the authors' institution's radiology data bank was manually searched for the mandibular anatomy that most closely mimicked the patient's mandible in consideration for reconstruction. The inter-condylar dimension was taken as a reference for transverse dimension whereas a normal value of FH-NPog angle (angulation between Frankfort horizontal plane and Nasion-Pogonion line) was taken as a sagittal reference to look for a close match. It was also made sure that the mandibular arch form of the chosen data grossly coordinated with the maxillary arch form of the patient, i.e., in class I skeletal relation (Figure 4). Figure 1: Virtual planning flowchart for creation of defect template. Figure 3: Designing template in category II. (**A**) 3-dimensional view of defect. (**B**) Segmentation of the remaining mandible on the left side (blue color). (**C**) Mirroring to the right side (red color). (**D**) Superimposing the current CT scan axial view to previous MRI. (**E**) Drawing the residual defect (red). (**F**) 3-dimensional view of virtually reconstructed defect (red). (**G**) Merging the segmented part, mirrored part and drawn part to form whole simulated mandible for printing (purple color). Figure 2: Designing template in category I. (**A**) 3-dimensional view of defect. (**B**) Segmentation of right hemimandible (blue color). (**C**) Mirroring to the left side (pink color). (**D**) Merging both sides to form simulated whole mandible for printing (yellow color). In all cases, the reconstruction templates of various defects were 3D printed with medical grade printing material. The templates were cold sterilized and reconstruction plates were bent to the contour only after mandibular resection was completed so as to keep room for alteration in reconstruction plan as per the scenario on the table (Figure 5). Figure 4: Designing template in category III. (**A**) 3-dimensional view of defect. (**B**) Appropriate mandibular anatomy selected from radiology data bank taking intercondylar distance as horizontal reference (red color). (**C**) Frankfort Horizontal Plane (FHP)-Nasion Pogonion (NPog) angle used as sagittal reference (87 \(\pm\) 4 degrees being the normal range). (**D**) Arch form coordination approximately matched with maxilla.