The effect of immersion fluids on soft lining materials

OBJECTIVES: Denture soft lining materials have the viscoelastic properties similar to oral mucosa. They facilitate more equal distribution of occlusal load to supporting bone under removable appliances. However, the durability of suitable visco-elasticity varies with the oral environment and material type, in an unpredictable way. This study investigated the effect of long term storage in different immersing fluids of two soft lining materials on fluid uptake and hardness. MATERIALS AND METHODS: Two heat-polymerised soft lining materials were tested; one a plasticised methacrylate material[1], and the other a silicone material[2]. Thirty specimens of each material were fabricated and subdivided into five groups. Each group was then stored in one of five immersing fluids (distilled water, artificial saliva, 10% and 50% ethanol and HB307) at 370C. Percentage weight changes and Shore A hardness were calculated at the following intervals: baseline, 0.5, 1, 2, 4, 6 hours, 1, 2, 3, 7, 14, 21, 28, 56, and 112 days. RESULTS: Vertex Soft showed significantly higher Shore A hardness values than Molloplast-B over the entire experimental period. Increased hardness was seen for Vertex Soft in HB307. A substantial weight variation was seen for Vertex Soft in HB307 and 50% Ethanol. Cyclical change in weight and hardness value occurred at similar time for Vertex Soft immersed in 50% Ethanol. CONCLUSIONS: Different immersing fluids have variable effects on weight change and hardness of the test materials. [1] Vertex Soft, Dentimex BV, Holland, [2] Molloplast-B, Karl Huber GmbH & Co. Germany.