THE DEVELOPMENT OF NEW SOFT LIMING MATERIALS

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It is generally recognized that there is no really satisfactory denture soft (resilient) lining material. At the state of art conference on restorative materials in Washington in 1986, J.W. Stanford stated "The resilient liners suffered principally from lack of permanence. This area appears to be one needing additional research support". Recent research has shown that a major cause of failure is the high water sorption of such materials and hence our objective is to produce elastomeric polymers with limited water uptake, and hence longer life. Greater comfort and less cost are also desirable properties. The aims of this study are therefore: 1) To develop new soft lining materials based on a) novel elastomeric methacrylate systems; b) silicone/acrylic adduct systems, to achieve low water sorption. 2) To analyze and characterize the most successful soft lining material to date, Molloplast B. 3) To study in detail the water sorption from pure water, aqueous solutions and artificial saliva, of the materials developed. This will test the hypothesis that water uptake is controlled by water soluble impurities in the polymer. Furthermore, it will help to evaluate why Molloplast B has low water uptake. 4) To evaluate the materials that exhibit low water uptake in terms of mechanical, visco-elastic and microbiological properties. 5) To evaluate the ability of solid-state NMR measurements to characterize dental polymers well enough to detect significant differences in molecular motion as a function of chemical structure as well as monomer and water content. The hypothesis to be tested is that changes in relaxation times provide a measure of molecular motion. Three groups of materials based on silicone products, powered elastomers and solid commercial elastomers will be studied. These materials require synthesis or special processing for preparation. The formulations do not involve plasticizers that leach out during service performance. Successful formulations will be obtained based on selection criteria which involve three stages of screening. Synthesis and preliminary selection thresholds will be carried out at London Hospital Medical College, and characterization and entire integration of the program will be accomplished at University of North Carolina.