Abstract
Statement of the Problem:Bonding failure between acrylic resin and soft liner material and also gradual loss of soft liner resiliency over time are two impending challenges frequently recognized with a denture base embraced with a resilient liner. Since patients drink various beverages, it is crucial to assess the influences of these beverages on physical characteristics of soft liners.Purpose:This in vitro study envisioned to assess the influence of food simulating agents (FSA) on the hardness of a silicone soft liner by employing a Shore A durometer test and also evaluate its bond strength to a denture base resin by using tensile bond strength test.Materials and Methods:To test the hardness of samples, 50 rectangular samples (40 mm × 10 mm × 3 mm) were prepared from a heat-polymerized polymethyl methacrylate (Meliodent). Mollosil, a commercially available silicone resilient liner, was provided and applied on the specimens following the manufacturer’s directions. In order to test tensile bond strength, 100 cylindrical specimens (30 mm × 10 mm) were fabricated. The liners were added between specimens with the thicknesses of 3 mm. The specimens were divided into 5 groups (n=10) and immersed in distilled water, heptane, citric acid, and 50% ethanol. For each test, we used 10 specimens as a baseline measurement; control group. All specimens were kept in dispersed containers at 37ºC for 12 days and all solutions were changed every day. The hardness was verified using a Shore A durometer and the tensile bond strength was examined by an Instron testing machine at a cross-head speed of 5 mm/min. The records were analyzed employing one-way ANOVA, Tukey’s HSD, and LSD tests.Results:The mean tensile bond strength ± standard deviation (SD) for Mollosil was as follows for each group: 3.1 ± 0.4 (water), 1.8 ± 0.4 (citric acid), 3.0 ± 0.4 (heptane), 1.2 ± 0.3 (50% ethanol), and 3.8 ± 0.4 (control). The hardness values for each group were: 28.7 ± 2.11 (water), 33.2 ± 2.82 (citric acid), 39.2 ± 4.8 (heptane), 32.3 ± 3.56 (50% ethanol) and 22.2 ± 2.08 (control). Mean values for hardness indicated that all of the food simulating agents significantly increased hardness of the Mollosil soft liner compared to the control group (p<0.05). The results of tensile bond strength depicted that water and FSA decreased the bond strength of the soft liner -denture base resin compared to the control group and it was statistically significant (p<0.05).Conclusion:The food simulating agents could influence the mechanical properties of silicone soft liners; hence, clinicians should inform their patients concerning their possible adverse effects and complications.
Highlights
Soft resilient liners or denture liners, due to their short- or long-term cushioning effects, are used in the inner surface of the denture base to improve the fitness of the denture, help to rehabilitate and condition inflamed tissues, and achieve more equal distribution of masticatory forces [1]
We divided specimens into 5 groups of 10 specimens to test both hardness and tensile bond strength (TBS) as Group 1: specimens tested for base line quantities, Group 2: specimens dipped in distilled water for 12 days, Group 3: specimens dipped in heptane for 12 days, Group 4: specimens immersed in citric acid for 12 days, and Group 5: specimens immersed in an aqueous 50% ethanol solution for 12 days
The results of hardness and tensile tests of specimens immersed in water and four food simulators for 12 days are shown in Table 2 and Figs. (1, 2)
Summary
Soft resilient liners or denture liners, due to their short- or long-term cushioning effects, are used in the inner surface of the denture base to improve the fitness of the denture, help to rehabilitate and condition inflamed tissues, and achieve more equal distribution of masticatory forces [1]. Tg is the temperature at which a polymer ceases to be glassy and brittle, and changes to a rubber-like form [1,2,3] These materials are generally used to provide a cushioning effect in patients with severe ridge resorption, severe bony undercuts, and congenital or acquired defects of the palate. These materials may be employed as soft liners during the healing time following implant placement [1,2,3,4,5,6,7]. Soft liners are used to cover the Several types of resilient liners are used for prosthetic purposes These liners are either acrylic resin-based or silicone-based. Tear strength, tensile bond strength (TBS), elongation, and Shore A hardness (SH) should be examined to assess the characteristics of long-term soft liners [12]
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