Effect of tissue conditioners on the dynamic viscoelastic properties of a heat-polymerized denture base

Statement of problem. Little is known about the influence of tissue conditioners on physical property alteration of denture base resins. Purpose. This study evaluated the influence of a variety of commercial tissue conditioners on alteration of viscoelastic properties of a heat-polymerized denture base acrylic resin. Material and methods. Four tissue conditioners and 1 heat-polymerizcd denture base acrylic resin were used. In one experiment, acrylic resin specimens (1.0-mm thick) were immersed in the liquid component of tissue conditioners for 36 hours. In another experiment, tissue conditioners were applied to acrylic resin specimens (0.5-mm and 1.0-mm thick) in a 2-mm layer; the specimens then were immersed in distilled water for 1 week. Control specimens for both groups had no lining and were immersed in distilled water for 36 hours and 1 week, respectively. Dynamic viscoelastic properties of the acrylic resin specimens were measured at 37degreesC with an automatic viscoelastometer. Tensile storage modulus (E'), tensile loss modulus (E), and loss tangent (tan delta) were determined at 1 Hz. These parameters were compared with analysis of variance and the Dunnett test at a predetermined significance level of .05. All statistical comparisons were made with reference to the control group and not to each other. Results. Only the liquid of Hydro-Cast significantly reduced E' and increased tan delta of the acrylic resin (P<.05). Acrylic resin specimens 0.5-mm thick and lined with tissue conditioners tended to have lower E' and higher tan 5 than the control. However, only Hydro-Cast and SR-Ivoseal significantly decreased E', and only Hydro-Cast raised tan 5 of the acrylic resin (P<.05). No significant difference was found among the E values. The tissue conditioners did not affect E', E, or tan 5 of acrylic resin specimens 1.0-mm thick. Conclusion. Within the limitations of this study, some tissue conditioners significantly plasticized the denture base acrylic resin 0.5-mm thick. However, when the acrylic resin was 1.0-mm thick, no plasticization by the tissue conditioners was noted.