Effect of ultraviolet protective agents on maxillofacial silicone elastomer, part 2: Mechanical properties after artificial aging.

Statement Of Problem: The addition of ultraviolet (UV) protectives may affect the materials' mechanical properties, which can limit the service life of facial prostheses.

Purpose: The purpose of this in vitro study was to investigate the effect of UV protectives on the mechanical properties of maxillofacial silicones after artificial aging.

Material And Methods: Six color groups (unpigmented, white, yellow, red, blue, and mixed) of addition-type maxillofacial silicone were prepared. Four UV protectives, benzophenone-3 (UV-BP), ethylhexyl methoxycinnamate (UV-EM), titanium dioxide (UV-TD), and ethylhexyl salicylate (UV-ES), at 0.5% and 1% concentrations by weight were incorporated into the silicone before polymerization. The specimens were subjected to accelerated aging in a weathering chamber for 300 and 600 hours and to thermocycling. The tensile strength and percentage elongation, tear strength, and hardness of maxillofacial silicones were evaluated. Data were analyzed by using 4-way ANOVA. The differences were compared by the Tukey honestly significant difference test (α=.05).

Results: Tensile strength decreased after 300 and 600 hours of UV aging in 0.5% and 1% UV-BP protective-added groups and increased in thermocycled groups (P<.05). Aging conditions generally showed no effect on the tensile strength of UV-EM, UV-TD, and UV-ES added groups (P>.05). Aging generated a decrease in percentage elongation values compared with nonaged specimens of groups (P<.05). The addition of UV protectives generally did not significantly affect the tear strength of specimens compared with control in the aged groups (P>.05). The hardness of UV protective-added groups increased when compared with that of nonaged groups after 300 and 600 hours of UV aging (P<.05). Also, thermally aged groups showed increased hardness than nonaged groups (P<.05).

Conclusions: The protective UV-BP addition caused decreased tensile strength, percentage elongation, and tear strength in both concentrations. The UV-EM and UV-ES provided increases in tensile strength and percentage elongation of the silicone in the 0.5% concentration. The addition of UV-BP, UV-EM, and UV-ES did not make significant differences; however, UV-TD significantly decreased the hardness values of the silicone.