Influence of Imidazolium-Based Ionic Liquids on Acrylic Denture Base Materials

Objectives: The aim of this study is to evaluate the effect of four different ionic liquids on the physical properties of heat-activated acrylic resins.
Methods: 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI.NTf₂), 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (OMI.NTf₂), 1-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF₄), and 3-(carboxymethyl)-1-methyl-imidazolium chloride (CMIM.Cl) were synthesized. The ionic liquids were incorporated into 5, 10, or 15 wt.% in the mixture of powder:liquid (2:1 by weight) of a commercial heat-activated acrylic resin. One group remained without ionic liquid as a control. The samples were tested for Knoop hardness (n=5), roughness (n=5), and flexural strength (n=5).
Results: The incorporation of any concentration of BMI.NTf₂ did not change the hardness compared to the control (p>0.05). The addition of BMI.BF₄ or CMIM.Cl decreased the hardness regardless of the concentration added compared to control (p<0.05). BMI.NTf₂ at 5% showed no difference compared to OMI.NTf₂ at 5% (p>0.05). BMI.NTf₂ at 10 or 15% showed higher hardness compared to the other ionic liquid groups at the same concentrations (p<0.05). The incorporation of 5, 10, or 15% of BMI.NTf₂ did not change the flexural strength compared to control (p>0.05). The addition of up to 10% of OMI.NTf₂ showed no difference compared to the control (p>0.05). BMI.BF₄ or CMIM.Cl at any concentration decreased the flexural strength compared to the control (p<0.05). BMI.NTf₂ and OMI.NTf₂ had no differences within the same concentration at 5 or 10% (p>0.05). At 15%, BMI.NTf₂ showed higher flexural strength than 15% of OMI.NTf₂, BMI.BF₄, or CMIM.Cl (p<0.05). CMIM.Cl groups showed no difference in roughness compared to BMI.BF₄ 10% and BMI.BF₄ 15% (p>0.05). These five groups presented higher roughness than others (p<0.05).
Conclusions: The addition of BMI.NTf₂ up to 15% in acrylic resin did not change the evaluated physical properties of the heat-activated acrylic resin. BMI.NTf₂ should be further tested as a novel anti-fungal agent for acrylic denture base materials.