In vitro hardness, water sorption, and resin solubility of laboratory-processed and autopolymerized long-term resilient denture liners over one year of water storage

Statement of problem. The clinical properties of resilient denture liners may be influenced by the method by which they are polymerized. Purpose. This in vitro study investigated material property changes of 2 new resilient denture lining materials that represent 2 different curing modes: autopolymerization and conventional laboratory processing. Material and methods. Two silicone-based liner products were tested; one was allowed to autopolymerize (Tokuyama Soft Relining Paste), and the other was laboratory processed (Luci-Sof). Ninety-six disk-shaped specimens (31 X 10 mm) were fabricated in aluminum ring molds for hardness testing. Sixty bar-shaped specimens (44 X 8.5 X 1.2 mm) were fabricated in aluminum molds for water sorption and resin solubility testing. Shore A hardness was determined directly after specimen fabrication and after 1 day, 1 week, 1 month, 6 months, and 1 year of water storage at 37°C. Water sorption and resin solubility were determined at the same time intervals. Analysis of variance and appropriate t tests were used to determine the effect of immersion duration both within and between the products tested. All statistical testing was performed at α = .05. Results. The hardness values of the laboratory-processed material were consistently greater than those of the autopolymerized material. After 1 week of water storage, the hardness of the autopolymerized specimens stabilized, whereas the hardness of the laboratory-processed specimens increased with immersion duration. Water sorption values for the 2 test products were similar after 6 months and after 1 year of water storage. At 1 month, 6 months, and 1 year, significantly lower resin solubility (P<.05) was recorded for the autopolymerized specimens compared with their laboratory-processed counterparts. Conclusion. Within the limitations of this study, the laboratory-processed material was harder than the autopolymerized product and demonstrated greater resin solubility over time. The latter result was not expected.