Overdenture retention of four resilient liners over an implant bar

STATEMENT OF PROBLEM: Resilient denture liners offer an alternative method of designing implant-retained overdentures. Space is provided in the overdenture to envelop the implant bar with a resilient liner to be applied chairside or processed in the laboratory. The degree of retention may vary and these materials change over time. PURPOSE: This study evaluated the retention on an implant/bar prosthesis with overdentures lined with 4 resilient denture lining materials, after cyclic insertion and removal over a simulated 1.5-year period. MATERIAL AND METHODS: Four implants were placed in a mandibular edentulous cast and a gold bar superstructure was made. Overdentures were processed in Lucitone-199 and Tokuyama, Luci-Sof, Molloplast-B, and PermaSoft (with and without sealer) lining materials, cured according to manufacturers' instructions. Each of 5 overdentures contained each liner and were cycled 2740 times (simulating 1.5 years of service at 5 insertions daily) in 37 degrees C water in an Instron at 20 cm/min. Insertion and retention force were measured. RESULTS: The 3 silicone rubber liners were 3 to 5 times more retentive than the plasticized acrylic liner initially. After cycling, Tokuyama soft liner (autopolymerized silicone) gained 14% retention, Luci-Sof (heat-cured silicone) gained 8%, Molloplast-B (heat-cured silicone) lost 12%, whereas PermaSoft (autopolymerized plasticized acrylic) with sealer lost 43%, and without sealer lost 60%. PermaSoft lining material also chafed and crumbled after cycling and was significantly less retentive in most statistical comparisons. CONCLUSIONS: All the silicone-based resilient liners retained the overdentures well. The plasticized acrylic was less retentive initially, and lost significant retention after 2740 cycles, compared with silicone-based resilient liners.