Mechanical Properties and Color Stability of Nano-oxides Pigmented Maxillofacial Elastomer

Objectives: The principal reasons for replacement of facial prostheses are degradation in color and mechanical properties. The purpose of this study was to evaluate the effect of 2 nano-oxides (commercial UV-light protection) combined with silicone pigments on the mechanical properties and color stability of a silicone elastomer before and after artificial aging. Methods: Two types of nano-oxides [Nano Zinc oxide (ZnO) and Nano Titanium oxide (TiO2)] were combined at 1%, 2%, 3% concentrations with A-2000 silicone elastomer. Silicone intrinsic pigments were added (control=no pigments). All specimens (N=5, Total of 280) were tested. Both physical properties and color measurement were recorded before and after aging in an artificial aging chamber at 450 kJ/m2. CIE L* a* b* values were measured by spectrophotometer. Hardness (ASTM D2240), tensile strength (ASTM D412), tear strength (ASTM D624) and elongation were measured using a universal testing machine. For each property, 3-way ANOVA and Fisher's PLSD test were performed to determine if there were statistically significant differences (p<0.05). Results: After artificial aging, all concentrations of both nano-oxides improved the tensile strength and elongation (P<0.05). 1% and 3% ZnO and 2% TiO2 improved the tear strength (P<0.05) when compared to control groups. For hardness after artificial aging, specimens of control groups were 4-7 times harder than all nano-oxide groups (P<0.001). Overall, ZnO provided better protection to this silicone than TiO2 after artificial aging. For color stability, Detal E* values of the mixed groups of all concentration of nano-oxides were significantly below the 50:50% acceptability threshold (Delta E*=1.1-1.8, below 3.0) when compare to control groups (Delta E*=2.6) (P<0.001). Overall, TiO2 provided better protection to this silicone than ZnO after artificial aging (Delta E*of TiO2=1.1-1.2 and Delta E*of ZnO=1.5-1.8). Conclusions: Nano-oxides improve color stability and mechanical properties of A-2000 silicone elastomer after subjected to artificial aging.