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Background The approximate life span of a silicone maxillofacial prosthesis is as short as after 4-14 months of usage, then a new prosthesis should be fabricated. But now many researchers have been directed toward improvement of properties silicone elastomeric materials. The objective of this study is to evaluate the effect of aging on tensile strength of two types of silicone materials used in the maxillofacial prostheses (VST-30 and VST-06) after artificial weathering for 100, 200 and 300 hours, and then comparing between the two selected materials in terms of selected artificial weatheringperiods. Material and methods a sample of 160 specimens were prepared anddivided into two main groups according to the types of elastomeric silicone (VST-30 and VST-06). Then each group subdivided into 8 divisions, (n=10). Two groups, one for clear and one pigmented as control groups before experimental weathering .While the experimental groups divided into clear and pigmented groups treated with artificialweathering for 100, 200 and 300 h. Results after different weathering cycles theresults show that there was no significant difference in the tensile strength for VST-30 silicone material pigment before and after weathering. While there was a highly significantdifference in the tensile strength for VST-06 pigmented silicone before and after weathering. Both VST-30 and VST-06 non-pigmented groups showed a highly significant change in the tensile strength after different weathering cycles. Conclusionsthe superior type for mechanical properties after difference cycles weathering was for VST-30 and incorporation of rayon flocking prevents the silicone materials from rapid degradation under artificial weathering and this may lead to increase in the service life of silicone prosthesis.

Background The approximate life span of a silicone maxillofacial prosthesis is as short as after 4-14 months of usage --- then a new prosthesis should be fabricated. But now many researchers have been directed toward improvement of properties silicone elastomeric materials. The objective of this study is to evaluate the effect of aging on tensile strength of two types of silicone materials used in the maxillofacial prostheses --- VST-30 and VST-06 after artificial weathering for 100 --- 200 and 300 hours --- and then comparing between the two selected materials in terms of selected artificial weathering periods. Material and methods a sample of 160 specimens were prepared and divided into two main groups according to the types of elastomeric silicone --- VST-30 and VST-06. Then each group subdivided into 8 divisions --- n=10. Two groups --- one for clear and one pigmented as control groups before experimental weathering .While the experimental groups divided into clear and pigmented groups treated with artificial weathering for 100 --- 200 and 300 h. Results after different weathering cycles the results show that there was no significant difference in the tensile strength for VST-30 silicone material pigment before and after weathering. While there was a highly significant difference in the tensile strength for VST-06 pigmented silicone before and after weathering. Both VST-30 and VST-06 non-pigmented groups showed a highly significant change in the tensile strength after different weathering cycles. Conclusions the superior type for mechanical properties after difference cycles weathering was for VST-30 and incorporation of rayon flocking prevents the silicone materials from rapid degradation under artificial weathering and this may lead to increase in the service life of silicone prosthesis.