# Fabrication and Analysis of a Ti6 Al4V Implant for Cranial Restoration
## 2 Methodology
### Modeling  
The main objective of this step was the designing of a customized cranial implant through the mirroring technique. Certainly, the mirror reconstruction technique can be identified as an influential and most extensively employed implant design technique in medical restorative applications, especially in animal anatomy where bi-lateral symmetry prevails [28]. It can also be established here that the anatomical structures acquired through mirroring are practically ideal and optimal [29; 30]. Figure 2: Image processing stages in Mimics®: (**a**) Coversion of DICOM files; (**a**) Reconstructed 3D skull model; (**b**) Bone identification; (**b**) Skull model with neck region; (**c**) Application of region growing technique; (**c**) Obtaining region of interest. The modeling stage commenced with the importing of 3D model's STL file (Figure 3a) in 3-Matic 9.0(R) (Materialize NV, Belgium) software. The following workflow adopted to accomplish the mirroring which assumed human anatomy to be symmetric. * The cranium was segregated through datum plane (mid-plane) after determining two maximal endpoints (Figure 3b,c). * The deformed or the deficient left side was taken out through the cutting operation (Figure 3d,e). * The normal or healthy bone on the contralateral side was imitated with reference across the center plane (or symmetric plane) (Figure 3f). * Merging and wrapping operations were carried out to minimize the disparities, inconsistencies and discontinuous surfaces between them (Figure 3g). * Consequently, a Boolean subtraction procedure (Figure 3h) was executed among the freshly designed skull model (Figure 3g) and the original skull containing defect (Figure 3a). * The mirroring procedure generated the tailored cranial implant (Figure 3i) with a thickness of \(\simeq 5.76\) mm (thickness of the cranial bone). The mirrored model assured a simple and precise fitting through the edge of the defective region as well, as it resulted in an implant contour which was perfect in terms of aesthetics and appearance. An impeccable alignment of the newly designed personalized cranial implant (red area) adjacent to the defective skull region (orange region) can be seen in Figure 4.  
Figure 3: Steps involved in the design of customized cranial implant in 3-Matic®: (**a**) Reconstruction of 3D skull model; (**b**) Generation of midplane; (**c**) Cutting of skull model; (**d**) Splitted model; (**e**) Removal of defected side; (**f**) Mirroring of right side; (**g**) Merging of two sides; (**h**) Application of Boolean subtraction; (**i**) Customized implant; (**j**) Skull with fitted Implant. As a result of redundant implant thickness, the likelihood of the stress shielding effect across the surrounding bone also increased. Therefore, to minimize the thickness and weight of the implant nearer to the bone counterpart, an offset operation was implemented on the thick cranial implant (Figure 5a,b). Finally, an implant with a thickness in the range of \(\simeq\)1.76-2 mm was obtained, as shown in Figure 5c. Moreover, the quadruple fixation mini-sheets with taper screw holes were also designed as shown in Figure 6a. They were needed to achieve the stability, sturdy connection and fixation of the implant on to the cranium as shown in Figure 6b. The tapered designed screw holes as a result of the entire sinking of the screws aided in the stability and rigidity as well as improving the patient's comfort. Figure 4: Precise fitting of custom built cranial implant on the deformed skull region. Figure 5: Thickness minimization and mini-plates attachment for fixing of screws: (**a**) Actual thickness; (**b**) Reduced thickness; (**c**) Implant fitted with mini-sheets. The FEA model was created to assess the biomechanical stability of the designed custom cranial implant [31]. The pre-processing, post-processing and the execution of the developed FEA model were performed in the Abaqus software.