## 2 Proposed Methodology
### Custom Implant Design  
The mandible model from MIMICS(r) was imported in 3-Matic(r) 13.0 (Materialise NV, Leuven, Belgium, 2018) software to model and custom-design the reconstruction plate. The steps involved in mirror reconstruction are explained in Figure 4. The mandibular STL file obtained from MIMICS(r) was imported in 3-Matic(r) (Figure 4a), where the left tumor region was cut down by a cut-and-punch operation (Figure 4b). The mandibular model was then split into two regions (Figure 4c), where the tumor region was removed (Figure 4d) for mirror operation. Mirroring was performed (Figure 4e) where the symmetrical healthy right mandibular region was mirrored to the left side. The two symmetrical right and left mandibular regions were then merged (Figure 4f) and wrapped to remove the voids and gaps (Figure 4g). The final obtained mirror model was then aligned with the mandibular tumor model (Figure 4h) to evaluate the anatomical positions. Upon closer examination of the aligned models, a small upper portion of the condyle regions mismatched the original tumor mandible. Several attempts at re-mirroring and re-adjustment failed to match the orientation to the original mandible.  
Figure 4: Steps involved in the three-dimensional reconstruction of the clean, healthy mandible using the mirroring technique.  
Figure 3: Segmentation of the region of interest (mandible) from the skull region.  
To overcome the misalignment between the mirroring and original tumor mandible, a newly design reconstruction technique was proposed. In this technique, the tumor model (Figure 5a) was cavity-filled to create a solid bone portion matching the original contours (Figure 5b). The benefit of such an approach was that it maintained the shape and anatomical geometry of the mandible. The additional bone portion of the tumor area was trimmed (Figure 5c), and the obtained cavity-filled mandible model was then aligned with the tumor mandible for evaluation (Figure 5d).  
Figure 6 explains the design steps involved in the resection of the mandible model, where the tumor part (Figure 6a) was resected using a cut-and-punch operation (Figure 6b,c). The resected model was the patient's mandible bony region on which the surgeons operated the implant after tumor removal. The resected tumor mandible (Figure 6d) was used for the 3D comparison and the fitting of the customized implant design in this study.  
Figure 7 explains the steps involved in the reconstruction of the customized implant design from the cavity-filled model. The obtained cavity-filled mandible model was loaded into 3-Matic(r) as an STL file (Figure 7a). The model outer part was selected using the brush mark technique (Figure 7b,c) and extracted for custom implant design (Figure 7d). Trimming and splitting operations were performed (Figure 7e,f) on the extracted bone mask to get an implant template (Figure 7g). An offset thickness of 2 mm was added (Figure 7h), and screw holes were incorporated for fitting (Figure 7i). The final obtained prefabricated custom-designed mandibular implant was aligned with the resected mandible for assembly and fitting evaluation (Figure 7j). The prefabricated implant designed from the cavity-filled model fitted precisely onto the tumor-resected mandible model as it was created from the bone itself. Similarly, a second prefabricated implant was also designed following a similar approach to that above from the mirror reconstruction model. These steps are presented to illustrate how the custom-designed implant was created from the healthy mandible after tumor removal through  
Figure 5: Sequential steps involved in the reconstruction of the mandible using cavity-filled technique.  
Figure 6: Design steps in the creation of resected mandible.  
a mirroring or cavity-filled approach. Hence, reconstructing a healthy mandible model is important whether through mirroring or cavity-filled approaches. The modeling and designing of the customized implant from the healthy mandible is the same for both models.