CHARACTERIZATION OF COMMERCIAL SOFT LINERS BY DYNAMIC-MECHANICAL ANALYSIS

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 ne w materials. One major weakness in the development of improved materia ls has been the lack of clear understanding of structure/property rela tionships. This paper deals with the determination of visco-elastic pr operties such as E'(Storage modulus) and tan delta (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 mat erials: (1) Molloplast B (silicone); (2) Novus (phosphazine); (3) Kure peet (fluropolymer); and (4) Super Soft (acrylic) was made using a Per kin-Elmer DMA-7. Samples were made following the manufacturers' instru ctions, in the form of sheets 1.5 mm thick and 15.0 mm square. The sam ples 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 ta n delta over a 5-95 degrees C temperature range. Water sorption was de termined gravimetrically at 37 degrees C. Changes in E' between the we t and dry conditions for Molloplast (B), Kurepeet and Super Soft were insignificant. A significant increase in tan delta for wet Novus was o bserved, suggesting that the material is capable of dissipating more e nergy. The 'wet' modulus (E') is abo ut 42% lower than the ''dry'' mod ulus (E'). Th is difference may be attributed to the very high water s orption (34%) of Novus. i.e. the significant decrease in E' indicates plasticization due to sorbed water. Changes in visco-elastic propertie s seem to occur for materials which take up large amounts of water at 37 degrees C. DMA is found to be a useful supplement for the evaluatio n of soft lining materials in conjunction with the standard mechanical test methods.