## 6 EBM Fabrication  
The finally obtained cavity-filled implant was produced through EBM technology. EBM is one of the latest rapid manufacturing techniques, which produces a fully dense part using a computer-controlled gun in a vacuum environment. EBM was first commercialized in 1997 by the Arcam AB Corporation now under General Electric [37]. The general principle of EBM is the selective melting of metal powder (Ti6 Al4V) in a layer-by-layer fashion using the electron beam of an electron emitted from the tungsten filament. The beam of electrons, as illustrated in Figure 16a, is controlled by three magnetic lenses, namely, the astigmatism lens, the focus lens, and the deflection lens. The astigmatism lens helps to generate a circular electron beam with a Gaussian energy distribution. The focus lens focuses and sharpens the beam into the smallest desired (0.1 mm) diameter. The deflection lens deflects the electron beam onto a specific target of the powder bed as per the CAD file. When the high-energy beam of electrons hits the metal powder, the kinetic energy is transformed into heat and melts the powder completely. After each melt cycle, the powder hopper holding the metal powder of 45 to 100 microns in size (Figure 16b) is lowered by one layer (50 microns), and the next layer of powder is fed onto the build platform using raking blades. This process is repeated until the completion of the build.  
When the build was completed, the build chamber was allowed to cool to 100 \({}^{\circ}\)C at 400 mbar through helium, followed by air. The cooled EBM build parts were then fed into a powder recovery system (PRS) (Figure 17) to blast away the semi-sintered titanium powder attached to the building part. All the blasted powder was recycled to minimize material loss. A filter screen and explosion-protected vacuum cleaner was also used to separate the coarse powder particles from the clean powder.  
Figure 18a illustrates the EBM-fabricated cavity-filled mandibular implant with attached support structures. The support structures provided gravity support for overhanging surfaces in order to dissipate the process heat and to minimize the geometrical distortions caused by the internal stresses [38]. However, the support structures had to be removed during post-processing. The support structures were attached to the building part by the teeth (Figure 18b) which could be easily removed  
Figure 16: (**a**) Schematic diagram of the electron beam melting (EBM) A2 machine and (**b**) scanning electron microscopic image of Ti6 Al4V powder.  
manually through players. The finally obtained titanium implant after support removal was precisely fitted onto the mandible model using bi-cortical medical screws, as shown in Figure 18c,d. This precise adaptation of the implant and bone counterpart helps in the reduction of surgical time and revision, in addition to providing better cosmesis [39].  
Figure 17: An Arcam EBM A2 machine (ARCAM AB, Molndal, Sweden) with accessories such as a powder recovery system and explosion-protected vacuum cleaner.  
Figure 18: EBM-produced cavity-filled reconstructed titanium implant (**a**) with support structures attached to the teeth (**b**) for easy removal. Front view (**c**) and side view (**d**) of precisely fitted titanium implant onto the FDM model with bi-cortical screws after support removal.