**2. Mechanical properties**

The mechanical properties of facial prostheses is very important since it directly related to durability of the prostheses. For 3D printing technology we proposed, a starch powder were used to print soft tissue prostheses by a Z-Corp Z510 3D printer and infiltrated using silicone polymers as the post processing. The mechanical properties of the composite produced by Z-Corp printer is tested here by comparing its' mechanical properties with object produced by silicone polymer using conventional technology [31].

Test models that were printed from starch by Z Corp 3D printer and infiltrated with maxillofacial silicone polymer—Sil-25 are shown in **Figure 2**.

Mechanical test for conventional technology is simulated using pure silicone polymers and used as control samples (**Figure 3**).

Pure silicone samples were designed according to ASTM specifications for tensile strength (Dumbbell-shaped specimens [32]), tear strength (Trouser-shaped specimens [33]), hardness test [34], and percentage elongation using solid work

#### **Figure 2.**

*Starch printed infiltrated silicone test samples for (A) dumbbell-shaped for tensile strength, (B) trouser-shaped for tear strength and (C) hardness test blocks.*

#### **Figure 3.**

*Silicone polymers test samples for (A) dumbbell-shaped for tensile strength, (B) hardness test blocks and (C) trouser-shaped for tear strength.*

2008 software for printing test samples and stainless steel molds were fabricated for the control samples (**Figure 4**).

Lloyd LRX tensile instrument applied to test tensile strength, tear strength and percentage elongation (**Figure 5**).

Shore Durometer Hardness Tester was applied to test the hardness of the 3D printed starch models infiltrated silicone polymers to be compared with pure silicone samples (**Figure 6**).

The collected data was analyzed using PASW statistics 18 to compare between the test group—3D printed samples and control group—pure silicone samples, Independent sample T test was utilized for the statistical analysis.

**Table 1**, Demonstrating the result of mechanical tests that reveals that test group—the 3D printed samples has significantly lower tensile, tear, and percentage elongation than control samples—pure silicone samples (*p* < 0.05). Whereas, a significant increase in the hardness of the printed samples compared to pure silicone samples (*p* < 0.05) as shown in **Table 1**.

The results indicated an increased hardness, and consequently the prostheses lose some flexibility, hardness is not the only issue that determine the flexibility, here the technology applied provide shell-like models and the prostheses built according to CAD/CAM is shell prosthesis showing high degree of flexibility than

**115**

**Figure 5.**

**Figure 4.**

handmade prosthesis despite increased hardness of the printed prostheses com-

Lower values of tensile, tear strength and percentage elongation do not indicate a critical problem if the patient maintained and handled the prosthesis gently, as a matter of fact the prosthesis does not require a very high tensile or tear strength

pared to pure silicone prostheses as shown in **Figure 7**.

*Lloyd LRX tensile tester testing tensile and tear strength of the printed samples.*

*Stainless steel molds for fabrication of control samples—pure silicone.*

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

**Figure 2.**

**Figure 3.**

**114**

the control samples (**Figure 4**).

*(C) trouser-shaped for tear strength.*

silicone samples (**Figure 6**).

percentage elongation (**Figure 5**).

*for tear strength and (C) hardness test blocks.*

samples (*p* < 0.05) as shown in **Table 1**.

2008 software for printing test samples and stainless steel molds were fabricated for

*Silicone polymers test samples for (A) dumbbell-shaped for tensile strength, (B) hardness test blocks and* 

*Starch printed infiltrated silicone test samples for (A) dumbbell-shaped for tensile strength, (B) trouser-shaped* 

Lloyd LRX tensile instrument applied to test tensile strength, tear strength and

Shore Durometer Hardness Tester was applied to test the hardness of the 3D printed starch models infiltrated silicone polymers to be compared with pure

The collected data was analyzed using PASW statistics 18 to compare between the test group—3D printed samples and control group—pure silicone samples,

**Table 1**, Demonstrating the result of mechanical tests that reveals that test group—the 3D printed samples has significantly lower tensile, tear, and percentage elongation than control samples—pure silicone samples (*p* < 0.05). Whereas, a significant increase in the hardness of the printed samples compared to pure silicone

The results indicated an increased hardness, and consequently the prostheses lose some flexibility, hardness is not the only issue that determine the flexibility, here the technology applied provide shell-like models and the prostheses built according to CAD/CAM is shell prosthesis showing high degree of flexibility than

Independent sample T test was utilized for the statistical analysis.

**Figure 4.** *Stainless steel molds for fabrication of control samples—pure silicone.*

#### **Figure 5.**

*Lloyd LRX tensile tester testing tensile and tear strength of the printed samples.*

handmade prosthesis despite increased hardness of the printed prostheses compared to pure silicone prostheses as shown in **Figure 7**.

Lower values of tensile, tear strength and percentage elongation do not indicate a critical problem if the patient maintained and handled the prosthesis gently, as a matter of fact the prosthesis does not require a very high tensile or tear strength

#### **Figure 6.**

*Hardness tester testing hardness of the printed samples.*


#### **Table 1.**

*Comparing the mechanical properties of the printed models with pure silicone models.*

unless the patient stretch his/or her prosthesis and handle it harshly. The patient should follow the instruction for maintenance cautiously so that to extend the prosthesis service life.

Investigations of mechanical properties (tensile, tear, hardness and percentage elongation) of the printed samples were significantly different from control samples. In this study the results of the mechanical tests performed on tensile strength, tear strength, the percentage of elongation and hardness for the printed samples were found to be significantly different from the control samples. According to results obtained from this study, no one can suggest that the manufactured prosthesis does not last long or not better than the handmade prosthesis, because the ideal properties have not been standardized yet in terms of the mechanical properties.

Variation in mechanical properties of the test samples compared with controlled samples—pure silicone samples could be perhaps due to amount of starch in the test material, as starch provides a scaffold for the silicone polymer when it is used by Z-Corp printer to produce three dimensional 3D facial prostheses. The starch

**117**

only 60%.

designed for

**Figure 7.**

*infiltrated silicone polymer.*

**3. Infiltration**

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

acts as filler for the 3D printed prostheses, a filler when added to the silicone polymer may increases hardness, and reduces tensile and tear strength, of course that is depend on the type and amount of the filler [35, 36]. Therefore, it was necessary to measure the weight or volume ratio of silicone polymers—the infiltrate to starch the filler. Furthermore, and in order to understand the variation in the mechanical properties and the general drawback in these properties it was necessary to investigate depth of penetration of the infiltrate (silicone polymers) inside the printed starch models the quality of this infiltration. Therefore, Proper protocols were

*(A) Method of infiltration leaving feather edged margin of the prosthesis. (B) Flexibility of printed prosthesis* 

3.Quality of infiltration and degree of coherence between the starch particles

For 3D printing soft tissue prostheses process, the 3D printed starch models is infiltrated by silicone polymers in order to provide skin texture and required elasticity and softness. The infiltration process affects overall quality of prostheses

As the starch powder implicated in fabrication of 3 dimensional soft tissue prostheses, it was necessary to determine the average amount of this powder within the total weight of prosthesis and their percentages by weight in the final prosthesis. in this investigation, 8 printed blocks of the starch powder (45 × 45 × 4 mm) were produced by Z510 printer. The blocks weighed using a sensitive digital balance (Mettler AJ100). Then the samples infiltrated with Sil-25 maxillofacial silicone polymers according to infiltration protocol mentioned in the previous section (3 bars for 25 minutes left for 25 hours) final setting time. Then the infiltrated blocks weighed again and percentage of each component within an infiltrated block was determined. **Table 2** shows weight in gram, standard deviation and percentage of each component. The powder adds up to 40% of the total weight of the fully infiltrated blocks, whereas the silicone polymers comprising

1.Percentage of starch by weight within fully infiltrated models

2.Depth of infiltration inside printed starch models

and therefore investigated below in different aspects.

and the silicone polymers.

**3.1 Silicone/powder ratio by weight**

### **Figure 7.**

*Prosthesis*

**Figure 6.**

**Table 1.**

*Hardness tester testing hardness of the printed samples.*

Silicone infiltrated starch (3D printing)

**Sample Tensile stress** 

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prosthesis service life.

Silicone (Convectional)

unless the patient stretch his/or her prosthesis and handle it harshly. The patient should follow the instruction for maintenance cautiously so that to extend the

*Comparing the mechanical properties of the printed models with pure silicone models.*

**(PSI)**

Average 455.98 10.77 30.89 480.75 SD 32.20 2.60 0.71 84.40

Average 170.45 8.02 62.80 221.46 SD 36.10 1.68 2.782 51.44

**Tear stress (N/mm)**

**Hardness Elongation** 

**(%)**

Investigations of mechanical properties (tensile, tear, hardness and percentage elongation) of the printed samples were significantly different from control samples. In this study the results of the mechanical tests performed on tensile strength, tear strength, the percentage of elongation and hardness for the printed samples were found to be significantly different from the control samples. According to results obtained from this study, no one can suggest that the manufactured prosthesis does not last long or not better than the handmade prosthesis, because the ideal properties have not been standardized yet in terms of the mechanical properties. Variation in mechanical properties of the test samples compared with controlled samples—pure silicone samples could be perhaps due to amount of starch in the test material, as starch provides a scaffold for the silicone polymer when it is used by Z-Corp printer to produce three dimensional 3D facial prostheses. The starch

*(A) Method of infiltration leaving feather edged margin of the prosthesis. (B) Flexibility of printed prosthesis infiltrated silicone polymer.*

acts as filler for the 3D printed prostheses, a filler when added to the silicone polymer may increases hardness, and reduces tensile and tear strength, of course that is depend on the type and amount of the filler [35, 36]. Therefore, it was necessary to measure the weight or volume ratio of silicone polymers—the infiltrate to starch the filler. Furthermore, and in order to understand the variation in the mechanical properties and the general drawback in these properties it was necessary to investigate depth of penetration of the infiltrate (silicone polymers) inside the printed starch models the quality of this infiltration. Therefore, Proper protocols were designed for

