Characterization of commercial soft liners by dynamic mechanical analysis

Abstract

Although there is a significant clinical interest in suitable polymer-based soft liners, none have proven fully satisfactory in actual use. As a result there has been continued interest in the development of new materials. One major weakness in the development of improved materials has been the lack of clear understanding of structure/property relationships. This paper deals with the determination of visco-elastic properties such as E′ (Storage modulus) and tan δ (damping factor) of four commercial materials. They represent the broad range of chemical types available for denture base soft liners. A DMA study of four materials: (1) Molloplast B (silicone); (2) Novus (phosphazine); (3) Kurepeet (fluropolymer); and (4) Super Soft (acrylic) was made using a Perkin-Elmer DMA-7. Samples were made following the manufacturers' instructions, in the form of sheets 1.5 mm thick and 15.0 mm square. The samples were tested compressively using a 3 mm flat tip probe cycled at a frequency of 1 Hz. Wet and dry specimens were evaluated for E′ and tan δ over a 5–95°C temperature range. Water sorption was determined gravimetrically at 37°C. Changes in E′ between the wet and dry conditions for Molloplast (B), Kurepeet and Super Soft were insignificant. A significant increase in tan δ for wet Novus was observed, suggesting that the material is capable of dissipating more energy. The ‘wet’ modulus (E′) is about 42% lower than the “dry” modulus (E′). This difference may be attributed to the very high water sorption (34%) of Novus. i.e. the significant decrease in E′ indicates plasticization due to sorbed water. Changes in visco-elastic properties seem to occur for materials which take up large amounts of water at 37°C. DMA is found to be a useful supplement for the evaluation of soft lining materials in conjunction with the standard mechanical test methods.