Effect of thermocycling on bond strength and elasticity of 4 long-term soft denture liners

Statement of Problem. Two problems found in prostheses with soft liners are bond failure to the acrylic resin base and loss of elasticity due to material aging. Purpose. This in vitro study evaluated the effect of thermocycling on the bond strength and elasticity of 4 long-term soft denture liners to acrylic resin bases. Material and Methods. Four soft lining materials (Molloplast-B, Flexor, Permasoft, and Pro Tech) and 2 acrylic resins (Classico and Lucitone 199) were processed for testing according to manufacturers' instructions. Twenty rectangular specimens (10 × 10-mm2 cross-sectional area) and twenty cylinder specimens (12.7-mm diameter × 19.0-mm height) for each liner/resin combination were used for the tensile and deformation tests, respectively. Specimen shape and liner thickness were standardized. Samples were divided into a test group that was thermocycled 3000 times and a control group that was stored for 24 hours in water at 37°C. Mean bond strength, expressed in megapascals (MPa), was determined in the tensile test with the use of a universal testing machine at a crosshead speed of 5 mm/min. Elasticity, expressed as percent of permanent deformation, was calculated with an instrument for measuring permanent deformation described in ADA/ANSI specification 18. Data from both tests were examined with 1-way analysis of variance and a Tukey test, with calculation of a Scheffé interval at a 95% confidence level. Results. In the tensile test under control conditions, Molloplast-B (1.51 ± 0.28 MPa [mean ± SD]) and Pro Tech (1.44 ± 0.27 MPa) liners had higher bond strength values than the others (P