A physico-chemical study of soft lining materials for acrylic dentures
Although soft lining materials are inadequate to their requirements, their use is widespread. - This investigation has been undertaken in an attempt to determine which are the better materials and how they may be evaluated. In addition some new materials have become available which may have advantages over existing materials. A representative selection of thirteen commercially available soft lining materials were chemically analysed. These, together with four experimental materials, were subjected to laboratory investigation of their water absorption and water solubility; their visco-elastic properties and the effect on these properties of bonding the materials to poly (methyl methacrylate); their rupture properties; their wettability and their effect on the growth of Candida albicans. An attempt was made to relate these properties to the chemical composition of the materials. Their water absorption and water solubility was in general unacceptably high with the exception of two silicone rubber materials and an experimental acrylic resin material. Conversely their compliance was generally satisfactory, two experimental acrylic resin materials being the exceptions. Two extremes of resilience were recorded but either may prove clinically satisfactory. With the exception of three of the silicone rubber materials their rupture properties were satisfactory, and only an experimental natural rubber material demonstrated completely unsatisfactory adhesion to poly (methyl methacrylate), although other materials may be unreliable in this respect. Eleven of the materials demonstrated satisfactory wettability, the OTHclZ Femaining six including four of the rubber materials. Only four materials inhibited the growth of Candida albicans and the constituents responsible were identified. Concern was expressed regarding the tissue compatibility of some of the constituents. In conclusion, only three of the materials investigated merit further study, two silicone rubber materials and an experimental acrylic resin material which utilises a polymerisable plasticiser.