Changes in stress relaxation property and softness of soft denture lining materials after cyclic loading

Objectives. Soft denture lining materials show varied and changeable stress relaxation property and softness under cyclic loading conditions. The purpose of this study was to determine the changes in the stress relaxation property and the softness of commercial soft lining materials after cyclic loading. Methods. One plasticized acrylic-based material (Coe Soft: COS) and two silicone-based materials (Mucosoft: MUS; Sofreliner S: SFL) were investigated. For each material, 10 cylinder-shaped specimens were subjected to 29 days of cyclic loading, 1800 times per day; other 10 unloaded specimens were used as control groups. Stress relaxation ratio and softness were measured after 1, 4, 8, 15, 22 and 29 days of cyclic loading or storage. Results. During 29 day period, the stress relaxation ratios of the cyclic loaded and unloaded COS, MUS and SFL specimens were 28.5-31.6% and 30.9-32.6%, 6.4-15.1% and 1.8-15.4%, 14.0-38.2% and 19.8-40.6%, respectively. The softness values of the cyclic loaded and unloaded COS, MUS and SFL specimens were 42.6-60.6% and 56.4-61.8%, 47.6-52.5% and 46.9-51.5%, 56.6-58.4% and 58.0-65.1%, respectively. Based on repeated-measures, 3-way ANOVA, the stress relaxation ratio was influenced by the loaded or stored period and the type of material (p < 0.05), but not by the application of cyclic loading; the softness value was influenced by the loaded or stored period and the application of cyclic loading (p < 0.05), but not by the type of material. Significance. Soft lining materials showed the loaded or stored period and the material type dependent stress relaxation properties regardless of the application of cyclic loading. Softness value was influenced by the loaded or stored period and the application of cyclic loading. (C) 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.