Viscoelasticity of Soft Denture Liners Comprised of Poly(EMA/BMA) and ATBC
Objectives: This study aimed to evaluate the influence of monomer type, plasticizer content and P/L ratio on the dynamic viscoelastic properties of light-cured, poly (ethyl methacrylate/butyl methacrylate) (poly(EMA/BMA)) and acetyl tributyl citrate (ATBC)-based soft denture liners. Methods: Two different monomers, iso-butyl methacrylate (i-BMA) and 2-ethylhexyl methacrylate (2-EHMA) solutions containing the plasticizer ATBC at 0, 25, 50 and 75 wt% were used as liquid components. Trace amounts of camphorquinone and ethyl p-dimethylaminobenzoate were added as the photo initiator and reducing agent, respectively. The liquids were mixed with poly(EMA/BMA) at a P/L ratio of 1.0 or 1.2, following which each mixture was exposed to a light-curing unit (Labo Light LV-III, GC Corp., Tokyo, Japan) for 20 minutes. Storage modulus (E’), loss modulus (E”) and loss tangent (=E”/E’) were determined at 1Hz and 37°C using a dynamic viscoelastometer (Rheovibron DDV-25FP, A&D Co. Ltd., Tokyo, Japan). Three-way ANOVA and t-tests were used to analyze the results (n=5), and the contribution ratio of each factor was determined. Results: ANOVA indicated that the contribution ratios of all viscoelastic values of the plasticizer content (E’: 57.1%, E”: 78.3%, loss tangent: 74.5%, p<0.0005) were higher than those of monomer type and P/L ratio. Higher ATBC percentage and lower P/L ratio exhibited significantly lower values of E’ and E” (p<0.05) in both i-BMA and 2-EHMA materials. These values of 2-EHMA materials tended to be lower than those of i-BMA materials. A higher loss tangent at 1 Hz demonstrates a greater degree of stress relief. All materials comprised of the monomer solution containing ATBC at 25 wt% produced higher loss tangent values than the other liquid combinations (p<0.05), except for the materials comprised of i-BMA at a P/L ratio of 1.2. Conclusions: 2-EHMA solutions containing ATBC at 25 wt% and a P/L ratio of 1.0 are suitable for light-cured soft denture liners.