Residual monomer: effect on tensile bond strength of silicone resilient liners
Adhesion failure between silicone resilient liner materials and denture base resin is a common problem found in clinical practice. Bond failure results in localized unhygienic conditions at the debonded regions and causes functional failure of the prosthesis. The aim of this study was to evaluate the tensile bond strength of 2 resilient liners (auto-polymerized silicone - Permafix® and heat- olymerized silicone - Permaflex®) under the influence of a residual monomer methylmethacrylate ([MMA]R) concentration. Two polymethyl methacrylate
(PMMA) specimens were prepared by implementing brass dies by means of a 3 mm thick spacer in a denture flask. Specimens (20 X 10 X 3 mm) were made by processing the resilient liners against the polymerized PMMA blocks. After polymerization, the brass spacer was removed from the mold, the PMMA
blocks were trimmed, and the bonding surfaces were smoothed. The PMMA blocks were placed back into the molds and resilient liners were packed into the space provided by the brass spacer, followed by trial packing and polymerization according to manufacturer instructions. Twenty specimens were prepared and
divided into 2 Groups (n=10) for each material: Group I (acrylic resin blocks were bonded to the resilient material immediately after processing), and Group II (blocks were bonded to the resilient material after storage in distilled water for 21 days at 37ºC, aimed at decreasing the residual MMA. Tensile bond strength was measured in a universal testing machine at a crosshead speed of 5 mm/min. Two-way ANOVA and Tukey tests were used to analyze the data (a=0.05). The results indicated that the materials tested showed a decrease in bond strength values (Group II). The silicone-based Permafix® had significantly (p£0.05) low mean values. Within the limitations of this in-vitro study, storage of acrylic resin-based liners in water before bonding with specimens of resilient liner Permafix® may not provide long-term clinical success.
Uniterms: Denture liners. Acrylic resins. Tensile strength. Methylmethacrylate.
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