Assessment of bond strength of four soft denture liners

Objectives: To determine the bond strength between four poly(organosiloxane) denture soft liners and a heat-cured acrylic resin denture base polymer. Furthermore, to evaluate the effect of bonding agents or primers on the PMMA denture base surface using SEM. Methods: The relining materials, Molloplast B (MLP), Flexor CC (FLX), Mucopren soft (MUP), Ufigel soft (UFG), and the denture base polymer Meliodent were used for preparing test specimens for each peel and lap-shear test setup. Mechanical testing was carried out in a Universal Testing Machine with a crosshead speed of 24 mm/min. All data were statistically analyzed by univariate ANOVA (alpha=0.05). SEM imaging technique was used to evaluate the fracture surfaces and the effect of different bonding agents on the surface of denture base polymer. Results: The material MUP gave the highest results (2,6 N/mm) for peel bond strength whereas MLP (1,57 N/mm) , FLX (1,27 N/mm) and UFG (0.99 N/mm) materials were found to be in the same statistical group (p>0.05). The material MUP gave the highest results (1,61 MPa) for lap-shear bond testing, but it was only significantly different from FLX (0,75 MPa) material (p<0.05). Failure types were visually classified as cohesive for MUP and MLP and adhesive for FLX and UFG. SEM imaging showed that the poly(methyl methacrylate) surface was influenced by the bonding agents differently, giving a relatively smooth surface for MUP to a relatively rough surface texture for FLX. Conclusions: Significant differences were found among materials with similar chemistry, probably because the bonding agents or primers were different. SEM imaging also showed that bonding agents or primers caused the PMMA surface to appear differently giving different poly(organosiloxane)/PMMA interface structures.