Influence of Plasticizer Type on Dynamic Viscoelasticity of Soft Liners

Objectives: This study evaluated the influence of various types of plasticizers on the dynamic viscoelastic properties and durability of heat-polymerized acrylic soft denture liners.
Methods: Three different plasticizers, acetyl tributyl citrate (ATBC), benzyl benzoate (BB), and butyl phthalyl butyl glycolate (BPBG) containing methyl methacrylate (MMA) at 40wt%, were used as liquid components. The liquids were mixed with poly(ethyl methacrylate) along with benzoyl peroxide (1.2wt%) at a P/L ratio of 1.5, then each mixture was polymerized in a water bath at 100°C for 1 hour. The specimens were immersed in artificial saliva for 28 days. Storage modulus (E’), loss modulus (E”) and loss tangent (= E”/E’) were determined at 1 Hz and 37°C using a dynamic viscoelastometer (Rheovibron DDV-25FP, A&D Co. Ltd., Tokyo, Japan). Solubility after 28 days of immersion was also determined using a desiccator containing silica gel. One-way ANOVA and Tukey’s multiple-range test were used to analyze the results (n=5).
Results: Loss tangent prior to immersion in artificial saliva was lowest for BB (1.04±0.01), followed by BPBG (1.21±0.08) and then ATBC (1.26±0.03), while percent change of loss tangent after 28 days was highest for BB (29.2±4.5%), followed by BPBG (-4.1±4.1%) and then ATBC (-3.0±1.9%). ATBC and BPBG each exhibited a significantly higher loss tangent and lower percent change of that value over time as compared to BB (p<0.05). A higher loss tangent at 1 Hz demonstrates a greater degree of stress relief. Values for percent solubility of materials containing ATBC (1.3±0.1%) and of materials containing BPBG (1.5±0.0%) were significantly lower as compared to BB (5.1±0.3%) (p<0.05).
Conclusions: These results suggest that ATBC is a suitable plasticizer for use with heat-polymerized acrylic soft denture liners based on its characteristics of dynamic viscoelasticity and durability.