Effect of artificial aging on color change and mechanical properties of high consistency maxillofacial silicone...

Discoloration and the deterioration of mechanical properties lead to the replacement of maxillofacial prostheses. However, studies on the change in color and mechanical properties of high viscosity elastomers are lacking.

The purpose of this in vitro study was to evaluate the influence of artificial aging on the mechanical and optical properties of high-consistency silicone elastomer (HCR) and compare these properties with a widely used liquid silicone rubber (LSR).

The specimens were fabricated from HCR (Derma-sil; Spectromatch Ltd.) and LSR (M511; Technovent Ltd.) silicone materials according to the manufacturers' instructions. A total of 325 specimens were used (50 for the tear test, 50 for the tensile and elongation test, 25 for the hardness test, 50 for absorption and solubility, and 50 for color and surface roughness measurements). Four subgroups of HCR with different Shore A hardness values (5, 20, 55, 70) were used. The specimens were subjected to tear (ASTM D624), tensile and elongation (ASTM D41215), hardness (ASTM D2240), absorption and solubility (ADA 12), surface roughness, and color change tests before and after the artificial aging process. Both water bath and ultraviolet (UV) chamber aging methods were used for the absorption and solubility tests. Contrast ratio and relative translucency parameters were also examined in addition to color change. Accelerated aging including UV light, humidity, and heat was carried out for 168 hours. The analyses were performed using 2-way factorial ANOVA and mixed ANOVA designs. Bonferroni multiple comparison test was used for significant results (α=.05).

The hardness values of all groups increased after aging except for the HCR subgroup with Shore A hardness 20 (P<.001). No significant change was found in surface roughness (P=.118), tear strength (P=.374), or elongation percentage (P=.053) after aging for all silicone groups. The only group with a significant change in tensile strength was HCR70 (P=.01). According to the water absorption results, absorption rates were significantly higher after artificial aging compared with bath aging in all silicone groups (P<.001) except LSR (P>.05). The aging method had significant effect on the water solubility of all groups (P<.001). Color change was significantly different among the silicone groups (P<.001).

The HCR silicone elastomer tested in the study showed optical and mechanical properties compatible with those of a commonly used LSR silicone.