Effect of Thermocycling on Physical Properties of Resilient Denture Liners

Objectives: To investigate the effect of aging on the surface roughness, tensile bond strength, and viscoelasticity on two denture resilient lining materials.
Methods: Liner materials based on acrylic resin: Dynamic Impression Liner (DIL) and Peripheral Resin II (PRII) were processed according to the manufacturer’s instructions. The specimens from each material were stored in 37 ±1°C distilled water for 24 hours then divided into three groups: before (control group; n =5) and after 1000 and 2000 thermal cycles (test groups; n =5) between baths of 5 ±1°C and 55 ±1°C. Surface roughness was recorded using a contact profilometer, tensile bond strength was determined with a universal testing machine, and viscoelasticity test was performed by dynamic rheometer. Data were analyzed statistically by independent Student’s t-test and one way ANOVA at the p < 0.05 level.
Results: DIL exhibited a significant increase (P<0.05) in surface roughness before and after thermocycling, and PRII showed an increase in roughness, but it was not significant (P>0.05). Tensile bond strength of DIL significantly increased after thermocycling (P<0.05) but decreased significantly (P<0.05) for PR II. Both materials demonstrated an increase in storage (E’), loss modulus (E”) loss tangent (tanδ) after thermocycling; however, the E’ and E” of PRII were higher than DIL. The dynamic viscoelasticity of DIL was more sensitive to changes in frequency than PRII.
Conclusions: Thermocycling significantly affected the physical properties of the denture liners. Both liners exhibited viscoelastic behavior and DIL had more marked change in properties over time (thixotropy) than PRII.