The Effect of Aging by Thermal Cycling and Mechanical Brushing on Resilient Denture Liner Hardness and Roughness

Purpose: The purpose of this study was to investigate the effects of aging on resilient denture liners. The aging effects were produced by using thermal cycling and mechanical brushing and were quantified as changes to surface hardness and roughness of resilient denture liners.
Material and Methods: A plasticized acrylic resin (Dentuflex) and two silicone-based (Molloplast-B, Sofreliner MS) resilient denture liners were examined. Pre- and post-test roughness and hardness measurements were recorded using a Surfcorder SE 1700 and Shore A durometer Teclock GS-709, respectively. Sixty specimens were manufactured; half were subjected to 3000 cycles in the thermal cycler (5 and 55°C). The remaining specimens received 30,000 strokes applied by a mechanical brushing machine followed by 3000 thermal cycles. Representative specimens from each group were observed under scanning electron microscope (SEM). Data were examined by multiple ANOVA, split-plot analysis, and Tukey test (α= 0.05).
Results: Shore A hardness values for Dentuflex, Molloplast-B, and Sofreliner MS soft liners were different from each other ( p < 0.05) before (79 ± 2.9; 40 ± 1.4; 33 ± 0.7) and after (80 ± 3.1; 40 ± 1; 34 ± 0.9) thermocycling. The surface roughness (in μm) of the same soft liner materials was significantly different ( p < 0.05) at the start (2.2 ± 0.4; 1.6 ± 0.6; 0.2 ± 0.1) but it was not different ( p > 0.05) after tooth brushing (1.7 ± 0.3; 1.7 ± 0.4; 1.9 ± 0.8) or thermocycling (1.6 ± 0.5; 1.6 ± 0.6; 1.5 ± 0.5)
Conclusion: Thermal cycling promoted increased hardness for Sofreliner MS and Dentuflex. Mechanical brushing promoted wear abrasion in Sofreliner MS and Dentuflex materials. Molloplast-B experienced no deleterious effects from either of the tests.