Objectives: The purpose of this study was to evaluate the influence of type of monomer on dynamic viscoelastic properties of cold-cured acrylic soft denture liners after setting. Methods: Five monomers methyl methacrylate (MMA), ethyl methacrylate (EMA), iso-butyl methacrylate (i-BMA), 2-ethylhexyl methacrylate (EHMA), 2-hydroxyethyl methacrylate (HEMA) containing dibutyl sebacate (DBS) at 50 and 75wt% were used as liquid components. 1.2wt% of p-tolyldiethanolamine was also added. These liquids were mixed with poly (ethyl methacrylate / n-butyl methacrylate) (50/50) along with benzoyl peroxide (1.2wt%) using a P/L ratio of 1.2. Storage modulus, loss modulus and loss tangent (= loss modulus / storage modulus) were determined at 1Hz using a dynamic viscoelastometer. Five tests were carried out for each material at 37 ^oC, 2 hours after specimen preparation. Results: Two-way ANOVA for the loss tangent indicated significant effects of the type of monomer (contribution ratio: 39.3%) and DBS content (contribution ratio: 25.5%) (p < 0.0005). The order of mean loss tangent of the materials with liquids containing 50wt% DBS was MMA:0.678(0.036); i-BMA:0.454(0.049); EMA:0.325(0.028); HEMA:0.286(0.017); EHMA:0.275(0.020). There were no differences among EMA, HEMA and EHMA. Other differences were significant (p < 0.05, ANOVA and SNK test). The order of mean loss tangent of the materials with liquids containing 75wt% DBS was i-BMA:0.302(0.073); EMA:0.292(0.025); MMA:0.278(0.024); HEMA:0.266(0.029); EHMA:0.204(0.053). EHMA exhibited significantly lower loss tangent than the other monomers (p < 0.05, ANOVA and SNK test). Conclusions: The results suggest that the viscoelastic properties of cold-cured acrylic soft denture liners can be controlled over a wide range by varying the type of monomer.

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