Bond Strength of Soft Liners to Fiber-Reinforced Denture-Base Resin

Purpose: This study evaluated bond strengths of four soft liners to fiber‐reinforced (FR) and unreinforced poly methyl(methacrylate) (PMMA) denture‐base resin. Materials and Methods: The autopolymerized denture‐base resin Palapress Vario (Heraus Kulzer GmbH, Hanau, Germany) was used as the substrate (15 × 15 × 5 mm3). The test group consisted of substrates reinforced with porous PMMA preimpregnated unidirectional glass fibers (Stick [StickTech, Turku, Finland]) (PMMA + FR group), and the control group was unreinforced acrylic resin (PMMA group) (n = 80 per group). One of four soft liners (Ufi Gel SC [Voco, Cuxhaven, Germany], Sofreliner Tough [Tokuyama Dental Corporation, Tokyo, Japan], Vertex SoftSil 25 [Vertex‐Dental B.V., Zeist, The Netherlands], and Eversoft [Dentsply Austenal, York, PA]) was placed and cured between two substrates using a polyethylene ring (10 mm inner radius, 3 mm height). Tensile bond strength tests (crosshead speed = 10 mm/min) were performed, and the results were analyzed using analysis of variance followed by Tukey's test (p= 0.05). Fracture surfaces were categorized as adhesive or cohesive‐mixed modes, and failure types were statistically analyzed using chi‐square test. Results: FR did not affect the bond strength results significantly (p > 0.05) except for Ufi Gel SC. Significant differences in bond strength were found among the reline materials (p < 0.001). FR specimens showed a significantly higher number of cohesive‐mixed fractures compared to unreinforced specimens (p < 0.05), except for plasticized acrylic‐based reline material (Eversoft [Dentsply Austenal]), which showed fewer cohesive‐mixed failures with FR. Conclusions: The choice of appropriate reline material system with FR acrylic resin is important for the soft liner/denture‐base polymer bond. Glass FR did not have a decreasing effect on the bond strength, except for Ufi Gel SC.