**4. Skin color reproduction**

Skin color is vital for quality of facial prostheses. Previous research has focused on reproducing skin color and assess their color appearance difference under standard lighting conditions [39, 40]. The advent of new lighting technologies such as Halogen and LEDs generates new challenges for rendering skin on displays, in print, but most importantly, for synthetically generated skin prostheses, since ambient illumination can change the appearance of both natural and synthetic skin, but not necessarily in the same way [41]. Here skin appearance models not only need to take into account different ambient illuminations, but also the three-dimensionally geometry of the human face and differences in the methods for reconstruction surgery, prosthetics or medical make-up/tattooing [42]. Therefore, to truly reproduce appearance of skin color under different illumination and objectively evaluate their color quality, follow steps are develop:

Step 1: Measurement of skin spectral reflectance of subject

The measurement of skin spectral reflectance would be affected by these various parameters, including the measurement instruments, measurement distance, measurement location, the instrument aperture size, the pressure applied to the skin by the instrument, as well as the gender and ethnic group [43]. Spectrophotometer is recommended for facial prostheses application, since it is independent of lighting applied and highly consistency [44].

Step 2: Develop spectral color profile for 3D camera

3D camera can be used to capture facial and body image. A spectral reflectance estimation need to conduct to transform camera RGB to spectral reflectance for each pixel of 3D image [45]. Spectral color database [46, 47]need to be used as training sample to obtain base function for spectral reflectance estimation.

Step 3: Develop spectral color profile for 3D printer

For 3D color printing, spectral color profile also needs to develop to transform spectral reflectance of human skin in each pixel of 3D image to printer CMYK value for color printing. Post printing processing also needs to conducted for infiltration process as described in previous section

Step 4: Color quality evaluation

To evaluate color quality of facial prostheses, the average CIELAB color difference (ΔEab) under several standard CIE illuminants needs to calculated. To test spectral reproduction, the root-mean-square error (RMSE) and goodness-of-fit coefficient (GFC) needs to apply [48].

#### **5. Discussion**

Drawback in the mechanical properties of the printed samples mostly attributed to the amount of starch (40%) and due to lack of coherence and integrity between the hydrophobic silicone polymers and the hydrophilic starch powder that form the scaffold for the test samples as Z Corp 3D printer utilizing starch powder for printing which led to draw back in the mechanical properties of the final product. Perhaps the prostheses will have a shorter service life than the conventional pure silicone prosthesis. However, printing several prostheses at time of printing could compensate the drawback in the mechanical properties. The technology applied enabled construction of several copies of the prostheses in a shorter time frame and at a lower cost than handmade silicone polymer prostheses. Another advantage of applying rapid prototyping is that producing the required thickness of the missing part that rendering a lightweight prosthesis, which is mostly valued by the patients (**Figure 13**).

**123**

**Figure 14.**

*Nasal prostheses produced by Z510-3D color printer.*

**Figure 13.**

*Optimization of Maxillofacial Prosthesis DOI: http://dx.doi.org/10.5772/intechopen.85034*

Furthermore, designing a prosthesis by using 3D software package can also allow the anaplastologist to save the design and all patients data to utilize it for printing future copies of the prosthesis on the patients' demand and with only light modification in the design of the prosthesis if there is any tissue change at the site of the

*3D printed nasal prosthesis showing nostril opened due to controlled thickness of the prosthesis.*

### *Optimization of Maxillofacial Prosthesis DOI: http://dx.doi.org/10.5772/intechopen.85034*

Furthermore, designing a prosthesis by using 3D software package can also allow the anaplastologist to save the design and all patients data to utilize it for printing future copies of the prosthesis on the patients' demand and with only light modification in the design of the prosthesis if there is any tissue change at the site of the

#### **Figure 13.**

*Prosthesis*

**4. Skin color reproduction**

their color quality, follow steps are develop:

applied and highly consistency [44].

process as described in previous section Step 4: Color quality evaluation

coefficient (GFC) needs to apply [48].

**5. Discussion**

Step 1: Measurement of skin spectral reflectance of subject

Step 2: Develop spectral color profile for 3D camera

Step 3: Develop spectral color profile for 3D printer

Skin color is vital for quality of facial prostheses. Previous research has focused on reproducing skin color and assess their color appearance difference under standard lighting conditions [39, 40]. The advent of new lighting technologies such as Halogen and LEDs generates new challenges for rendering skin on displays, in print, but most importantly, for synthetically generated skin prostheses, since ambient illumination can change the appearance of both natural and synthetic skin, but not necessarily in the same way [41]. Here skin appearance models not only need to take into account different ambient illuminations, but also the three-dimensionally geometry of the human face and differences in the methods for reconstruction surgery, prosthetics or medical make-up/tattooing [42]. Therefore, to truly reproduce appearance of skin color under different illumination and objectively evaluate

The measurement of skin spectral reflectance would be affected by these various parameters, including the measurement instruments, measurement distance, measurement location, the instrument aperture size, the pressure applied to the skin by the instrument, as well as the gender and ethnic group [43]. Spectrophotometer is recommended for facial prostheses application, since it is independent of lighting

3D camera can be used to capture facial and body image. A spectral reflectance estimation need to conduct to transform camera RGB to spectral reflectance for each pixel of 3D image [45]. Spectral color database [46, 47]need to be used as training sample to obtain base function for spectral reflectance estimation.

For 3D color printing, spectral color profile also needs to develop to transform spectral reflectance of human skin in each pixel of 3D image to printer CMYK value for color printing. Post printing processing also needs to conducted for infiltration

To evaluate color quality of facial prostheses, the average CIELAB color difference (ΔEab) under several standard CIE illuminants needs to calculated. To test spectral reproduction, the root-mean-square error (RMSE) and goodness-of-fit

Drawback in the mechanical properties of the printed samples mostly attributed to the amount of starch (40%) and due to lack of coherence and integrity between the hydrophobic silicone polymers and the hydrophilic starch powder that form the scaffold for the test samples as Z Corp 3D printer utilizing starch powder for printing which led to draw back in the mechanical properties of the final product. Perhaps the prostheses will have a shorter service life than the conventional pure silicone prosthesis. However, printing several prostheses at time of printing could compensate the drawback in the mechanical properties. The technology applied enabled construction of several copies of the prostheses in a shorter time frame and at a lower cost than handmade silicone polymer prostheses. Another advantage of applying rapid prototyping is that producing the required thickness of the missing part that rendering a lightweight prosthesis, which is mostly valued by the patients

**122**

(**Figure 13**).

*3D printed nasal prosthesis showing nostril opened due to controlled thickness of the prosthesis.*

**Figure 14.** *Nasal prostheses produced by Z510-3D color printer.*

defect [28]. Finally we believe that the many limitations of handmade prostheses regarding esthetics, high prosthesis cost, time, effort, hectic impression techniques and problems of retention plus high technical skill required for fabrication by anaplastologist could be generally reduced and consequently minimizing the social and psychological challenges that often-maxillofacial patients encountered in life.

At this stage, a fully computerized customized prosthesis is manufactured, using biocompatible materials [49]. The prosthesis matching the patient's skin color and having skin-like texture with accurate anatomical details of the patient, possessing a light weight with controlled thickness of the prosthesis that is well appreciated by the patients as shown in (**Figure 14**).

Despite the many advantages of this technology in constructing soft tissue facial prostheses, there were few limitations compared to handmade—conventional method of fabrication. These limitations were related to the mechanical properties of the final product [50]. The mechanical tests shows drawback in the mechanical properties, however, it is hard to judge how poorly that will affect the prosthesis on the patient; the only real way of testing mechanical and optical durability is when the prostheses test on the patients during the service life of the prosthesis. As the project was at the experimental stage of development it wasn't possible to perform these tests on patients [28]. More work should be done to determine how long the prostheses would last. So far it is obvious that the prostheses done need to be replaced regularly. Further investigations should be done on the printing materials in order to improve the mechanical properties and durability of the prostheses and to achieve optimal advantages of time compression technology and rapid prototyping for simple, full automated fabrication of facial prostheses.
