The Japan Academy of Maxillofacial Prosthetics started a project to develop silicone elastomers for facial prostheses in 2010. In 2015, GC Corporation launched Silfy® in the market as a soft relining material. In order to improve the quality of silicone materials for facial prostheses and to launch the materials, further basic and clinical research is required. The purpose of this study was to evaluate the viscoelastic properties of four experimental silicone materials （KRS-10, KRS-10F, KRS-C2B1, and KRS-C2P1, GC Corp）, and the effects of a thixotropic agent on the viscoelastic properties of KRS-10 and KRS-10F. Seven cylindrical-shaped specimens of each material were prepared. All specimens were stored in water at 37℃, and measured with a creep meter after 1 day, 1 week, and 1 month. The viscoelastic properties among materials and storage periods were analyzed with the two-way analysis of variance （ANOVA） and Tukey’s multiple comparison test. All silicone materials exhibited mainly elastic behavior. The viscoelastic properties of all the experimental materials examined showed almost the same behavior, and there were no differences between the cartridge and manual mixing types. The viscoelastic properties of these materials in this study were not influenced by aging within 1 month.
