Silica-filled elastomer/methacrylate systems as soft liners.

Denture soft lining materials are compliant cushions used at the oral tissue-denture interface. They are generally required to have sufficient compliance to redistribute mastication load, as well as an adequate modulus for long-term dimensional stability and control over the water uptake. This study investigated the effect of using silane treated fumed silica as a filler on the properties of experimental soft lining materials based on blends of isoprene-styrene (SIS) block co-polymer and mixtures of methyl methacrylate (MMA) and 1,6-hexandiol dimethacrylate (HDMA). The overall elastomer/monomer ratios were maintained, whereas the monomers ranged from 10 to 60% HDMA. The silica filler level was maintained at 10 wt% with respect to SIS. The properties investigated were the dynamic mechanical parameters of storage modulus (E') and tan delta as a function of temperature and the quasi-static mechanical parameters of ultimate tensile strength (UTS) and elongation to break (Eb) as well as absorption properties that were carried out in water and saline. In both unfilled and filled systems there was an increase in E' and a decrease in tan delta with an increase in HDMA. Silica addition tended to increase E' and substantially reduce tan delta in materials with less than 20% HDMA. UTS decreased with filler and HDMA content, however, Eb was greater for filled systems. Generally, in the long term, the water uptake decreased with increasing HDMA content and E'. The silanated silica further reduced the water uptake, indicating a cross-linking effect, thus increasing the restraining force on droplet growth. The uptake in saline was significantly reduced indicating an osmotically controlled uptake process.