Physical-property comparison of a chairside- or laboratory-polymerized permanent soft-liner during 1 year

Purpose: This investigation examined the influence of polymerization mode and water storage duration on the Shore A hardness, water sorption, resin solubility, and glass transition temperature of Permasoft, a commercial soft denture liner that is polymerized either chairside or in the laboratory. Materials and Methods: Specimen disks (31-mm diameter x 10 mm thick) and bars (44 x 8.5 x 1.2 mm) were polymerized following manufacturer's recommendations. The chairside polymerization process was simulated by pouring the mixed components into a mold and processing at 70°C for 15 minutes under 2-psi pressure. Laboratory-polymerized specimens of the same dimensions were fabricated by processing under 500-psi pressure at 100°C for 45 minutes. Specimens were stored in distilled water at 37°C for 1, 7, and 30 days, and 6 and 12 months. Specimens were tested for Shore A hardness, water sorption, resin solubility, and glass transition temperature after the prescribed interval. To determine the effects of polymerization mode and storage time on material properties, a repeated-measures ANOVA (hardness data) and a two-way ANOVA (sorption and solubility data) with appropriate post-hoc tests were used. Results: Shore A hardness values increased from a low of 9.4 (±0.5) units immediately after fabrication to a maximum of 15.9 (±1.1) units after 1 year. Mode of polymerization did not influence hardness (p = .9851). Water-sorption values ranged from 4.2 (±0.2%) of dry weight to 14.7 (±2.5%) after 1 year. Resin solubility varied from 10.3 (±0.6%) of preimmersion weight to 15.4 (±1.1%), and immersion duration had no effect on solubility. In addition, after 1 year of storage, no difference in resin solubility or water sorption was found with respect to cure mode. The glass transition temperature for chairside-polymerized samples approximated -10°C, while that for labpolymerized samples approximated -15°C. Conclusions: With regard to the material properties evaluated in this study, clinically processed Permasoft liner was equivalent to the laboratory-processed material.