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 degrees 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 alpha=.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.