The chemical degradation of denture soft lining materials : a study of the interactions between denture soft lining materials and food simulating liquids
Denture soft lining materials are used as a cushion between the hard denture base and the oral mucosa. Fluid sorption and solubility may contribute to material hardening, roughening, cracking or tearing, loss of adhesion to the hard denture base or contamination by extrinsic stains or yeasts. The ideal material is required to have low fluid uptake, good wettability, retain compliance and surface integrity, and not support fungal growth. Evaluation of behaviour in the oral environment is difficult and a number of materials, such as artificial saliva and food simulating liquids, have been recommended to simulate the environment. The two types of denture soft lining materials commonly used in clinical practice are methacrylate and silicone based. These together with an experimental elastomer were evaluated in this study. Fluid sorption and solubility were determined by immersion of disc specimens in food simulating fluids (distilled water, 3% acetic acid, 10% ethanol and 50% ethanol) and artificial saliva at 37±1°C with weighing at set time intervals. Similar experiments were carried out using liquids representing fatty food constituents with coconut oil and 1113307H. ardness was determined using a Shore A durometer. In order to determine wettability, contact angle was measured using a computer microscope. The surface roughness was assessed using a non-contact laser profilometer. Finally, an attempt was made to identify leachable substances from the materials investigated using a Fourier transform infrared spectrometer. An additional part of this study was to look at the adhesion of one yeast species Candida albicans to commercial materials using various protective coatings to determine their efficacy. The resultsd emonstratedth at the type of liquid simulating foods or artificial saliva, and immersion time significantly influenced the behaviour of the commercial denture soft lining materials and the experimental elastomer during in vitro testing. The two groups of materials behaviour were different. The two methacrylate-basedd enture soft lining materials showed marked absorption and solubility which may be associated with the loss of plasticisers. The two silicone-based denture soft lining materials showed much less absorption and solubility under the same conditions. The experimental elastomer showed marked swelling in oils, which was not expected, its chemical structure being similar to a methacrylate. Shore A hardness remained unchanged during the fluid immersion with the two silicone-based materials but showed measurable changes with the two methacrylate-basemd aterials and the experimentale lastomer,I ncreaseds urface roughness was also demonstrated with the two methacrylate-based materials, and decreasedc ontact angle was found with the two silicone-basedm aterials. After various surface treatment, coconut oil reduced Candida albicans adhesion in all cases.