Effect of storage duration on the hardness and tensile bond strength of silicone- and acrylic resin-based resilient denture liners to a processed denture base acrylic resin

Abstract

Statement of problem: Two potential problems commonly identified with a denture base incorporating a resilient liner are a failure of the bond between the acrylic resin and resilient liner material and a loss of resiliency of the resilient liner material over time.

Purpose: This investigation evaluated the effect of storage duration on the tensile bond strength and hardness of acrylic resin- and silicone-based resilient liners that were either heat- or autopolymerized onto denture base acrylic resin.

Material and methods: The denture liners investigated were a definitive acrylic resin-based heat-polymerized (Vertex Soft), interim acrylic resin-based autopolymerized (Coe-Soft), definitive silicone-based heat-polymerized (Molloplast-B), and definitive silicone-based autopolymerized (Mollosil Plus) resilient liner. The resilient liners were processed according to manufacturers' instructions. The resilient liner specimens for tensile bond strength testing (n=10) were 10 x 10 x 3 mm and were processed between 2 polymethyl methacrylate (PMMA) (Meliodent) blocks (40 x 10 x 10 mm). The resilient liner specimens for hardness testing (n=10) were 20 mm in diameter and 12 mm in height. Specimen shape and liner thickness were standardized. Specimens were stored for 1 day, 1 week, or 1, 3, or 6 months in water at 37 degrees C. Tensile bond strength was measured in a universal testing machine at a crosshead speed of 20 mm/min, and hardness was measured using a Shore A durometer. Two-way ANOVA and Tukey HSD tests were used to analyze the data (alpha=.05).

Results: The results indicated that there were significant differences both in the hardness and bond strength values of resilient liner materials. The definitive silicone-based heat-polymerized (Molloplast-B) resilient liner had significantly higher bond strength and lower hardness values than the others. Prolonged exposure to water produced significantly higher hardness values and lower bond strength values.

Conclusions: Within the limitations of this in vitro study, specimens of resilient liners immersed in water demonstrated significantly (P<.001) lower bond strength values and higher hardness values over time.