Silica-filled elastomer/methacrylate systems as soft liners

Abstract

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.

Long-Term Soft Denture Lining Materials

“…In addition, different methods for sorption and solubility calculations have been used, such as percentage changes in mass [67,95] or mass changes per unit volume [55]. Additionally, in some studies, uptake during aging has been measured as a percentage weight change between the initial weight and the weight at a given time [96]. Thus, the results from different studies might be difficult to directly compare, but they illustrate the effects of various factors on the measured properties.…”

“…This process creates locations for the formation of water droplets, and then, the droplets grow until their osmotic pressure reaches the same level as the external solution, or it is fixed by elastic forces [95]. Many factors, such as the degree of cross-linking, the polymer structure, and the presence of fillers or liquid, can affect the transport of liquid through elastomeric polymers [96]. The use of silane treatment fillers with coupling agents is a widely accepted method for altering the mechanical properties of elastomers; however, this method can also reduce water uptake.…”

“…The use of silane treatment fillers with coupling agents is a widely accepted method for altering the mechanical properties of elastomers; however, this method can also reduce water uptake. The lack of compatibility of the filler with the polymer can also cause the formation of voids at the interface and can lead to increased water absorption [96]. For instance, Waters et al [97] analyzed the effects of incorporating three different surface-treated hydrophobic silica fillers into experimental RTV SLTSDL materials, and the authors observed a large reduction in sorption.…”

“…In several studies [102,103,104,105], it has been stated that an ideal soft lining material should have the same viscoelasticity as the alveolar mucosa. However, soft lining compensates for deficiencies of the mucosa, and mimicking the mechanical behavior of their viscous flow causes a reduction in the rate of shape recovery, which is considered to be unfavorable during transfer of the cyclic mastication load [96,106,107,108]. In general, time-dependent deformation can be regulated with the glass transition temperature by adding plasticizers to reduce intimate contact between the polymer chains [109].…”

“…Based on these contrasting results [103,113], it can be hypothesized that the obtained effect on the loss modulus was dependent on the efficiency of compounding the filler and on the chemical bonding between the surface-treated filler and the polymer matrix. In [96], a reduction in tan δ was observed with increasing concentrations of silanized silica in experimental elastomer/methacrylate soft linings based on blends of isoprene–styrene block co-polymer and mixtures of methyl methacrylate and 1,6-hexanediol dimethacrylate. The addition of silica increased the storage modulus values, which remained at satisfactorily low levels only for materials with dimethacrylate monomer concentrations ranging from 10% to 20%.…”